ESBD_File_342668_Experience Chemistry (PDF File).pdf

Get Connected!

GO ONLINE

to experience Matter, Energy, and Change in your world!

Wildfires, rocket launches, and car engines.

Explore the matter and energy in a rocket launch in a virtual lab.

INVESTIGATION 1

2 Investigation 1 Matter, Energy, and Change

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Connect your understanding of matter and energy to a career as a forest and conservation worker.

Watch an animation that explains matter, energy, and change in a car engine.

Read about heat flow in your Experience Handbook.

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Why are wildfires so difficult to extinguish?

ANCHORING

PHENOMENON

GO ONLINE to Engage with real-world phenomena by watching a video and completing a CER interactive worksheet.

4 Investigation 1 Matter, Energy, and Change

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INVESTIGATION 1

The biomass of forests burns as a result of combustion, a chemical reaction. If there is a climate cycle of a wet period, which generates a lot of biomass, and a dry period, which causes that biomass to die and dry out, then there may be huge forest fires that burn out of control. Once you have viewed the

Anchoring Phenomenon video and used the claim-evidence-reasoning worksheet to draft an explanation, answer the following reflection questions about wildfires.

Matter, Energy, and Change

1 THEME Energy and Matter Where did the mass of the forest trees come from? What happens to that mass when the forest burns?

2 SEP Develop a Model Why don’t trees spontaneously catch on fire and burn all the time? Why don’t fires stop immediately as soon as they start?

Develop a model for what has to happen for a large fire to occur.

TEKS 6B, 9A, 13A,

13B, 13C, 13D, 14B, 1A, 1G, 3A

Anchoring Phenomenon 5

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EXPERIENCE 1

Introduction to Energy

Matter and Energy in Systems Chemistry is all about matter: things that have mass and take up space, or have volume. The universe is made out of matter and energy. Ordinary matter is composed of very small particles called atoms. In chemistry, you study the interactions of atoms and the subatomic particles that make them up, including the electrons that bind atoms together.

In chemistry, you will investigate chemical interactions. In every case, changes occur within a system that has interacting components. These changes are driven by transfers and/or transformations of energy. Defining a system and its components is a way to understand the changes that occur in any part of nature, whether it is a chemical system, a biological system, or the solar system. Changes within a system involve a movement of matter driven by a flow of energy. If anything is happening, then energy is flowing.

If there is no flow of energy, then nothing happens.

3 THEME Systems and System Models What are the parts of this water wheel system? Label the water wheel to show the matter and forms of energy that flow through the system.

GO ONLINE to Explore and Explain the energy content of foods, fuels, and other everyday materials in your life.

TEKS 13A, 1A

READING

Use Visuals In a small group, discuss how energy changes forms in the water wheel figure. Identify a similar energy change in your life. What forms of energy are in your example? Describe the example to the group. ELPS 4.F

6 Investigation 1 Matter, Energy, and Change

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4 SEP Develop Models Describe the many different forms of energy involved with stretching and releasing a rubber band. What other processes are similar to this model?

A stretched rubber band contains stored elastic potential energy.

Elastic energy is a type of mechanical energy.

When the rubber band is released and is in motion it has kinetic energy.

Movement is also a type of mechanical energy.

Energy is the capacity to move, do work, change matter, or produce heat.

Energy can be hard to define because it takes many different forms and can do many different things.

Potential Energy The energy stored within a system due to the positions of its parts is called potential energy. Every substance has a certain amount of energy stored inside it.

Matter is made of atoms that are often bonded together. The energy stored in chemical bonds is known as chemical potential energy. The energy stored in the nuclei of atoms is nuclear energy. Gravitational and elastic are two other types of potential energy.

Kinetic Energy The energy of an object’s motion is called kinetic energy.

As with potential energy, there are several types of kinetic energy. Electrical energy can be a form of kinetic energy, through the motions of charged particles. Thermal energy is the total kinetic energy possessed by all of the individual particles that make up an object or substance. The particles that make up an object or substance have a range of kinetic energies. The average kinetic energy is the mathematical average of the individual kinetic energies of all the particles in a substance or object.

There are other forms of energy as well, such as electromagnetic radiation, which includes microwaves, X-rays, and visible light.

Definitions of Energy

1 Introduction to Energy 7

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Calories

17,335 steps

86 active minutes

The joule The SI unit of energy is the joule (J).

One joule of heat raises the temperature of 1 g of pure water 0.2390°C.

1 J = 0.2390 cal

The calorie The calorie (cal) is a non-SI unit.

One calorie of heat raises the temperature of 1 g of pure water 1°C.

1 cal = 4.184 J

Burning Calories During exercise, your body uses chemical reactions to break down sugars and fats. Like a fire, these reactions release heat, but in a controlled way.

For example, breaking down a sugar cube releases as much heat as burning it.

1 Calorie = 1,000 calories

Calorie (with a capital C) The energy content of foods and beverages is usually given in Calories.

Real-Time Health Data You may wear a health device to get real-time information as you exercise. These devices express energy in dietary Calories.

Units of Energy What units can you use to show how much energy?

A joule can also be defined in terms of mechanical energy.

1 J = 1 kg∙m2/s2

Nutrition Facts Serving Size 1 Bottle

Amount Per Serving

Calories 20

Total Fat 0 g

Sugars 12 g

Sodium 260 mg

Potassium 75 mg

% Daily Value

0%

4%

11%

2%

5 SEP Use Math How much energy has your body used, in joules, if your health device indicates that 450 Calories were burned during your workout? How many Calories are in a dinner containing 3.5 × 106 joules?

8 Investigation 1 Matter, Energy, and Change

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Energy Flow and Transformations Unlike matter, energy does not have mass or volume. You can only detect energy because of what it does. If you apply a force to a stationary object by pushing it, then energy has been transferred from you to the object. You can’t see the energy, but you can calculate it.

mass (kg) Kinetic Energy = 1 __ 2 mv2 velocity (m/s)

Gravitational Potential Energy = mgh acceleration height (m) of gravity (9.8 m/s2)

Thermochemistry is the study of energy changes that happen during chemical reactions and changes in state. In chemical reactions, substances change to other substances with a different amount of chemical potential energy.

You can detect those energy changes by observing heat transfer, work, or a combination of both. Heat is energy that transfers from one object to another because of a temperature difference between the objects. Heat flows spontaneously from a warmer object to a cooler object.

6 SEP Reason Quantitatively Show that the units of kinetic energy (from 1 __ 2 mv2) and of gravitational potential energy (from mgh) are the same.

Transforming Potential Energy The controlled explosions of the gasoline in the combustion chamber of a car‘s engine transform the chemical potential energy into kinetic mechanical energy that propels the car. Some of the potential energy is also transformed into heat.

Potential Energy When you buy gasoline, you are buying stored chemical potential energy.

1 Introduction to Energy 9

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Rate of Energy Flow The rate of energy flow in a chemical reaction or any other process is called power, and it is measured in watts (W). A watt is equivalent to 1 joule/second, or 1 kg∙m2/s3. You may be familiar with power from using electricity, which is the flow of electrons. Light bulbs are described by the number of watts of electrical power they use. But power is used to describe the flow rates for all energy transformations, including chemical reactions. Heat flow is the rate at which heat moves from one substance to another. The rate that a substance or a system warms during a chemical reaction can be measured in watts.

7 SEP Calculate Water flows over Niagara Falls at the average rate of 2,400,000 kg/s, and the average height of the falls is about 50 m.

Knowing that the gravitational potential energy of falling water per second = mass (kg) × height (m) × gravity (9.8 m/s2), what is the power of Niagara Falls? How many 15 W LED light bulbs could it power?

Power from Water The amount of power available from a waterfall is dependent on the amount of water flowing and the height of the falls. Compare the sizes of these two waterfalls.

The height and volume of this waterfall are much larger, resulting in greater gravitational potential energy and a higher rate of energy flow.

10 Investigation 1 Matter, Energy, and Change

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The First Law of Thermodynamics No matter what experiments you do in class, the first law of thermodynamics, also called the law of conservation of energy, requires that energy is neither created nor destroyed.

When energy is transferred or transformed from one system to another in any physical or chemical process, all the energy can always be accounted for.

Sometimes the transfer of energy is hard to see, especially in the case of chemical reactions. Take a pile of logs on a beach and burn them. The chemical potential energy that the logs initially have is transformed into heat and light as the logs burn. But what happens to that energy when only ash remains? All of the heat and light of the burning logs transform into thermal and kinetic energy of the sand, air, and water, and some amount of sound energy. If you could add up all the final thermal, kinetic, and sound energy, it would equal the chemical potential energy the logs lose when they burn. The energy is always accounted for, and most chemical interactions involve a transfer of heat.

8 SEP Develop Models Use the everyday example of heating a pot of water on a stove as a model to support an explanation of the scientific idea in the first law of thermodynamics.

9 SEP Develop Models Describe the energy inputs and outputs for the campfire. Use the first law of thermodynamics to develop a valid equation as a model to represent the campfire system that includes all the input and output energies involved.

Transforming Stored Energy As the logs burn, chemical reactions occur.

Energy stored in the logs is transferred to the products of the reactions and transformed to other types of energy.

The logs are fuel for the fire.

1 Introduction to Energy 11

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Boiling point of water

Freezing point of water

Human body temperature

373.15 K

273.15 K

310.15 K

100°C 212°F

0°C 32°F

37°C 98.6°F

Temperature Temperature is a measure of the average kinetic energy of the particles in matter. If you heat an object or substance by transferring energy to it, the atoms will move more vigorously, and its temperature will increase.

Temperature Scales In science, temperatures are measured using either the Celsius or Kelvin scale, though most of the United States still uses the Fahrenheit scale.

Use these mathematical expressions to convert temperatures from one scale to another.

°C = K − 273.15 K = °C + 273.15 °C = (°F − 32) × 5 __ 9

10 THEME Scale, Proportion, and Quantity How are the Celsius, Kelvin, and Fahrenheit scales similar? How are they different? Considering their differences, think of one scenario in which each scale is more convenient to use.

Celsius The Celsius scale is based on the freezing and boiling points of water. Those points are 0°C and 100°C, respectively, defined at standard atmospheric pressure.

Fahrenheit On the Fahrenheit scale, the freezing point of water is 32°F. The boiling point is 212°F.

Kelvin The Kelvin scale is based on the lowest temperature that is theoretically possible: 0 K, or absolute zero.

ANCHORING

PHENOMENON

Revisit

12 Investigation 1 Matter, Energy, and Change

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Average Temperatures

MF A JM J A S O N D

Month

Te m p er at ur e

F)

J

San Francisco, CA Richmond, VA

11 SEP Interpret Data Use the fact that water has a higher specific heat than rock (such as granite) to explain the differences in the temperature curves for the two cities in the graph.

Specific Heat and Climate San Francisco and Richmond are at about the same latitude.

San Francisco, on the Pacific Ocean, has less variation in temperature.

The Difference Between Temperature and Heat Temperature is measured in degrees. It is not the same as heat, which is measured in joules. Although an increase in heat causes an increase in temperature, the amount the temperature changes will vary, depending on the substance.

The amount of energy needed to raise the temperature of 1 kg of material by 1 degree K is called the specific heat (C ) and is expressed as J/kg∙K.

Specific heat varies for different materials. For example, the specific heat of granite is 790 J/kg∙K while the specific heat of water is 4181 J/kg∙K.

ANCHORING

PHENOMENON

Revisit

GO ONLINE to Elaborate and Evaluate your knowledge of energy by completing the class discussion and data analysis activities.

In the CER worksheet you completed at the beginning of the investigation, you constructed an explanation to answer a question about forest fires. With a partner, reevaluate the evidence you cited in your arguments.

12 THEME Matter and Energy Wood needs to be given heat energy to reach the temperatures required for combustion to begin. What property of the wood would you need to know to predict how fast the wood would start to burn? Explain.

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EXPERIENCE 2

Modeling Energy

A Conceptual Model of Energy Energy is itself a conceptual model, because energy isn’t a physical thing. You can’t see it or touch it. As energy flows between systems, you can develop and use models to represent it as a substance that can be quantified and must be conserved, but in fact, it is only conceptual.

Chemical equations describe the energy involved with changes in the composition, state, or phase of substances. However, you can only measure the reactants and products. You never see the energy itself. It helps to compare this to the way water flows down rivers and through hydroelectric dams, doing work along the way such as eroding river banks or generating electricity. Or how electricity in the form of electrons flows through electric circuits, doing work such as turning on lights. As with the moving water and moving electrons, chemical reactions are not themselves energy; they just carry the energy.

13 THEME Energy and Matter Develop an explanation of how energy drives the movement of matter and the ability to do work in the hammer system model shown. Your explanation should be supported by the model and consistent with scientific ideas about energy.

GO ONLINE to Explore and Explain the thermodynamics of a reaction in a bag and to find where California gets its energy.

Potential energy is stored in the relative distances between atoms.

When bonds break and distances change, chemical potential energy is converted into kinetic energy.

Chemical Potential Energy Molecules are held together by chemical bonds, which form through the electrical attraction between protons and electrons.

You can see evidence that the hammer has energy when the kinetic energy of the hammer does work in shaping a piece of metal.

As the cam turns, it lifts and drops the hammer repeatedly.

Mechanical Potential Energy A hammer raised by a cam on a turning wheel gains gravitational potential energy. When it drops, potential energy is converted to kinetic energy.

TEKS 13C, 1G

14 Investigation 1 Matter, Energy, and Change

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When change happens within or between systems, you can describe the changes using either forces or energy. Both will give you the correct answer because forces and energy are essentially the same thing.

Energy can be described as the result of forces acting over a distance.

For example, hydrogen (H) and oxygen (O) atoms will react to form water (H2O), releasing energy in the process. This chemical reaction can be described in terms of the energies of the substances before and after the reaction. It can also be described in terms of the forces of electromagnetic attraction between the electrons of bonded atoms and their nuclei.

You can’t see the hydrogen and oxygen atoms because they are too small. However, you can gain some understanding of the roles of energy and forces in chemical reactions when you look at larger physical systems that you can see. For example, when a book falls to the ground or when billiard balls collide, you can describe the interactions involved in terms of the forces between objects and as conversions of energy.

14 THEME Energy and Matter Imagine a pool ball that bounces off of a bumper and slowly comes to a halt. Explain what happened at each point in terms of applied forces and energy transfers.

Energy in Collisions When pool balls collide they apply forces on each other, transferring energy.

Energy and Forces The motion of a book that is falling can be described and quantified either in terms of force (from gravity) or energy (from the potential energy lost). As the book falls to the ground, the force of gravity acts on the book increasing its velocity.

The amount of kinetic energy when the book hits the ground is the same as the amount of gravitational potential energy at the top.

3. The first ball changes direction when it collides with the second ball. Frictional forces between the balls and table cause the balls to slow down.

2. It applies a force to a second ball when they collide. Some of first ball‘s kinetic energy is transferred to second ball.

1. The first ball begins moving when it‘s struck with a stick.

Forces and Energy

2 Modeling Energy 15

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Electrical Forces at Atomic Scales The structure and interactions of matter at the bulk scale are determined by electrical forces within and among atoms. The bulk scale is also called the macroscopic scale. Macroscopic is a term that describes a property of a substance or object that is large enough to see or measure without magnification, or an observation scale that does not require magnification.

Except for gravitational attraction, electrical forces govern almost all of our daily interactions, both at the atomic scale and the macroscopic scale. This includes chemical systems. The temperature at which a substance melts, how quickly a substance evaporates at a given temperature, and how atoms combine in a chemical reaction are all governed by electrical forces.

Opposites Attract The electrical force between particles with opposite charges is attraction.

A positively charged particle and a negatively charged particle are attracted to each other.

Like Charges Repel The electrical force between particles of the same charge is repulsion. Two positive charges repel each other.

Similarly, two negative charges repel each other.

15 SEP Develop Models Use the model of the system of two atoms to make a list of all of the attractive and repulsive forces between the negatively charged electrons and positively charged protons in these atoms. Note that the particles without a charge label are neutral.

16 Investigation 1 Matter, Energy, and Change

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Strength of attraction among particles

Alcohol Water Mercury

Energy States of Water

‒20

0 100

Solid

Gas

Liquid

Melting

Boiling

200 300 400 500 600 700 800

Te m p er at ur e

C

Heat Absorbed (calories per gram)Heat Absorbed (calories per gram)

‒40

Atomic and Bulk Properties The structure and behavior of substances at the bulk (or macroscopic) scale can be used to infer the strengths of electrical forces within and among atoms and molecules. For example, graphite and diamond are both made of carbon.

Graphite is often used in pencils because it‘s very soft. Diamonds are very hard and strong. The reason for the differences between graphite and diamond is the different strengths of the electric forces bonding their atoms together.

16 THEME Patterns Changes in the state of matter (solid, liquid, gas) are the result of different energy levels at the molecular level. Look at the graph of the energy required to go from water ice to water vapor. Describe the energy of the water molecules for each state.

Surface Tension Surface tension is another example of a property that differs depending on the electrical forces among atoms or molecules. The greater the force, the greater is the surface tension.

2 Modeling Energy 17

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Temperature Difference The flame has a higher temperature than the object, so heat flows from the flame to the object. The particles in the object closest to the flame begin to vibrate faster.

Heat continues to flow until all the particles are at the same temperature. All the particles in the object are vibrating faster.

17 SEP Plan an Investigation Design an experiment to show that the heat flow between adjacent objects of different temperatures is greater when the temperature difference is greater.

18 SEP Construct Explanations Suppose you fill a cup with room-temperature water and then pour in an unknown substance and a chemical reaction occurs. After a few minutes, you notice that the outside of the cup feels warmer than room temperature. Would the reaction be classified as an exothermic or endothermic process?

Heat flows from the flame to the object and from the warmer part of the object to the cooler part of the object.

The Direction of Heat Flow Heat flows from warmer to cooler objects. The greater the difference in temperature, the faster the heat flow. If your hands are cold, a hot heat pack will warm them up faster than a lukewarm heat pack.

In a chemical process, or chemical reaction, the end products can have either more or less energy than the reactants. That affects the direction of heat flow in the reaction. In a process classfied as an exothermic reaction, heat is released to the surroundings because the reaction products are at a lower energy level than the reactants. Heat packs use exothermic reactions.

In a process classified as an endothermic reaction, heat is absorbed from the surroundings because the reaction products are at a higher energy level than the reactants. Cold packs use endothermic reactions.

18 Investigation 1 Matter, Energy, and Change

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ANCHORING

PHENOMENON

Revisit

GO ONLINE to Elaborate on and Evaluate your knowledge of energy by completing the peer review and engineering design activities.

In the CER worksheet you completed at the beginning of the investigation, you constructed an explanation to answer a question about forest fires. With a partner, reevaluate the evidence you cited in your arguments.

19 SEP Construct an Explanation How does a forest fire model the energy flow of fuel combustion? Explain.

20 SEP Use Evidence You are reading an article in a local newspaper about forest fires that includes some ideas to decrease the number of forest fires. Read the following explanation. Then evaluate and critique the suggested solutions using empirical evidence and logical reasoning.

Forest fires can spread quickly through forests, especially forests that have experienced drought. The most important things we can do to make these forests more resistant to devastating fires is to thin out the forests by removing dead or sick trees, as well as clearing as much of the dry growth along the forest floor as possible. Not only will fuel be removed from the path of potential fires, water can be saved and better distributed among the healthy trees.

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Neutron

Proton

Conservation of Matter

A Conceptual Model of Matter Conceptual models of matter have some similarities to and some differences from models of energy. Like energy, matter can be tracked as it moves through and among systems. Matter, like energy, is also conserved— in chemical reactions, it can neither be created nor destroyed.

Unlike energy, matter consists of physical stuff, so you can touch it and hold it. You can also measure the quantity of matter. This is mass. In some situations it is sufficient to treat matter as a continuous substance, where bulk characteristics provide enough information. In other situations it is helpful to consider the components of matter (atoms and subatomic particles). The figure describes and models the structure of atoms, including the masses, electrical charges, and locations of protons and neutrons in the nucleus and electrons in the electron cloud.

Nearly all of the mass in the atom is in the nucleus, where positively charged protons and uncharged neutrons are bound together by the nuclear force. Protons and neutrons both have a mass of about 1 atomic mass unit.

21 SEP Develop Models With a classmate, think of an analogy to describe the structure of an atom. Describe the similarities between your analogy and the structure of an atom with a neighboring pair of classmates, and then describe the locations and electrical charges of the protons, neutrons, and electrons in an atom.

Negatively charged electrons move about the nucleus, forming the electron “cloud.” The mass of each electron is negligible when compared to that of a proton or neutron, only about 0.0005 atomic mass units.

EXPERIENCE 3

Atom Atoms are composed of three particles: protons, neutrons, and electrons. Most of an atom is empty space.

GO ONLINE to Explore and Explain the conservation of matter in combustion reactions.

TEKS 6B, 9A,

14B, 3A

20 Investigation 1 Matter, Energy, and Change

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F

62 pm e-

Cl

102 pm e-

F-

133 pm

Cl-

181 pm

156 pm

Na

191 pm e-e-

60 pm

95 pm

Li+

Na+

Proton

3 protons 3 neutrons 3 electrons

3 protons 4 neutrons 3 electrons

Li

Building Blocks of Chemistry

Protons in Atoms An atom’s protons determine an atom’s chemical identity. An atom of a particular element will always have the same number of protons.

For example, lithium always has 3 protons.

Protons and neutrons are nearly equal in mass.

The mass of an electron is considered to be negligible because it is more than 1830 times smaller than the mass of a proton or a neutron.

Isotopes Atoms can have different numbers of neutrons. Atoms of the same element that have different numbers of neutrons are called isotopes. Since neutrons have no charge, they do not change the electrical forces among atoms.

Isotopes not only have different masses but also have different physical properties.

Ions Atoms can also have different numbers of electrons.

Atoms of the same element that have different numbers of electrons are called ions. When atoms gain or lose electrons, the sizes of the atoms and the electrical forces they exert change.

Sizes are in picometers (10−12 m).

Positive ions that have lost an electron are smaller than their neutral atoms.

Negative ions that have gained an electron are larger than their neutral atoms.

What determines the mass and properties of atoms?

22 THEME Patterns Explain the observed pattern of how the sizes and charges of atoms change with the addition and subtraction of electrons.

3 Conservation of Matter 21

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Matter

Heat Heat

Open and Closed Systems Thermochemistry is the study of the heat exchanged between systems and their surroundings. In an open system, such as an open saucepan with boiling water, both matter and energy are transferred to the surroundings.

However, if you put a lid on the saucepan and create a closed system, matter cannot escape and is instead contained and conserved in the system.

If you added the amount of water vapor in the pot to the liquid water that cooled and condensed on the lid, you would find that they are the same as the amount of water that evaporated. In an isolated system, such as a an insulated beverage container, where the sides are insulated and a lid is screwed on tight, no energy or matter is transferred to the surroundings.

23 SEP Design Your Solution Biosphere 2 was an attempt to have humans live within a perfectly closed system, as a model for living on other planets. The first attempt failed because the system began losing CO2, which was chemically reacting with the exposed concrete walls. How would you go about designing a habitat that is a closed system? Explain how matter and energy would flow within the system.

Open In an open system, energy and matter are exchanged freely with the surroundings.

Closed In a closed system, matter is conserved, but energy is exchanged with the surroundings.

Isolated In an isolated system, neither energy nor matter is exchanged with the surroundings.

22 Investigation 1 Matter, Energy, and Change

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Measuring the Flow of Matter In chemistry, the flow of matter is modeled through equations that are similar to an equation you would use in algebra. When you write and balance chemical equations, the numbers and types of atoms must be equal on both sides because, according to the law of conservation of mass, mass is conserved and can neither be created nor destroyed in a physical change or chemical reaction. The masses on both sides of the equation must be equal. The numbers of atoms on both sides of the equations must also be equal.

2K + Cl2 ⟶ 2KCl

Subscripts show the number of atoms in a compound.

There are two potassium (K) atoms and two chlorine (Cl) atoms on each side of the equation.

Coefficients in front of chemical formulas indicate the number of atoms or molecules.

24 SEP Use Mathematical Thinking Iron (Fe) reacts with oxygen gas (O2) to form rust (Fe2O3). Balance the equation given for the synthesis reaction, using the law of conservation of mass. Rewrite the equation, including the approriate coefficients, to ensure that the same number of each kind of atom appears on both sides of the equation.

Fe + O2 ⟶ Fe2O3

Reactants Product

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Conservation of Matter During Combustion In combustion reactions, oxygen gas reacts with a molecule, often releasing energy in the form of both heat and light (a flame). The fuel that burns is often a hydrocarbon, containing atoms of both hydrogen and carbon. In all cases, matter is conserved during the reaction. The same numbers of atoms exist before and after the combustion reaction. In the combustion of propane, oxygen reacts with propane. The products of the reaction depend on the amount of oxygen present. But in all cases, the numbers of carbon, hydrogen, and oxygen atoms are conserved.

Complete Combustion In the presence of sufficient oxygen, complete combustion of propane produces water, carbon dioxide, and energy. Energy from the reaction is transferred to the pot of water on the burner.

25 SEP Reason Quantitatively Use the chemical equations for the complete combustion and the incomplete combustion of propane to show that matter is conserved in both situations.

Incomplete Combustion In the presence of insufficient oxygen, the incomplete combustion of propane produces water, carbon dioxide, carbon monoxide, and energy. Less energy is produced than with complete combustion.

A blue flame is an indicator of complete combustion.

A yellowish-orange flame is an indicator of incomplete combustion.

C3H8 + 5O2 ⟶ 3CO2 + 4H2O + Heat 2C3H8 + 9O2 ⟶ 4CO2 + 2CO + 8H2O + Heat

24 Investigation 1 Matter, Energy, and Change

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Combustion and Work The energy of combustion is used to generate heat and light, but it can also do work. Work, which you will learn more about in your physics class, is the product of the net force on an object and the distance through which the object is moved. Work has units of energy, so it’s measured in joules.

work (joules) = force (newtons) × distance (meters), or W = Fd

Rockets The expansion of hot gases during a combustion reaction can be used to push a piston, and that if several pistons are fired with the correct timing, they can power a car. Another, more direct, application of mechanical work using combustion is a rocket. In a rocket, solid or liquid fuels are burned to produce hot gases. Because the gases take up a much greater volume than the fuel, the rocket gets pushed in the direction opposite to the direction in which the gases expand. That is how NASA rockets reach the moon, Mars, and other planetary bodies.

Lift Off! The model rocket in the photo quickly gains speed and reaches its maximum height in a few seconds.

The rockets used by NASA burn for several minutes and can gain enough speed to escape Earth’s gravity.

Forces generated by the rapid expansion of the hot gases from a rocket‘s exhaust push the rocket upward.

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Generator

Air in Natural gas in

Gas turbine Boiler

Steam turbine

Exhaust

Electric power output

Generator

Steam out

W at er in

Cooling tower

Condenser

Gas-Powered Turbines One of the largest uses of combustion reactions is the burning of fossil fuels to generate electricity. In electric power plants driven by the burning of coal, natural gas, or oil, the heat given off by combustion produces expanding gas that pushes through a set of turbines, making them spin. A turbine is a rotary mechanical device that extracts energy from a flowing fluid and converts it into useful work.

Electricity-generating turbines run by combustion may be powered by burning gases, or they may be powered by steam that is produced in a boiler. The actual generation of electricity is done using wires and magnets, according to the laws of electromagnetism, but the energy originally comes from combustion.

26 THEME Energy and Matter Recall that force = mass × acceleration.

Explain why the acceleration of a model rocket increases over time, even if the force from the chemical combustion of the rocket fuel remains constant.

Natural gas is the commonest fuel to power a gas turbine.

Exhaust heat from the gas turbine produces steam that drives a steam turbine.

In the condenser, steam is cooled to water. Then it returns to the boiler.

Electricity Generation The diagram shows how energy, in the form of electricity, is generated from the combustion of natural gas.

26 Investigation 1 Matter, Energy, and Change

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Hydrogen nuclei Helium nucleus Positrons

Energy

Uranium-235 Uranium-236

Neutrons

Neutron

Energy

When Matter Isn’t Conserved During nuclear reactions, certain forms of matter can be created or destroyed, and matter, or mass, is converted into energy. Consider the equation E = mc2, where m is the mass (kg) and c is the speed of light in a vacuum, which is 300 million m/s. Since c is squared in the formula, making a very big number, you can see that converting a small amount of mass releases an enormous amount of energy. Matter is destroyed during fission, fusion, and the decay of radioactive elements such as uranium. Energy can also be converted into matter, which is often thought of as a form of energy.

So, although matter is not always conserved, energy is always conserved.

Comparing Fission and Fusion Reactions Fission is used in some power plants to make electricity. Fusion occurs in the center of stars such as the sun, releasing the energy you eventually see as sunlight. When you compare the models shown for fission and fusion reactions, you see that in fission, an atom splits, and in fusion, particles combine.

In one fission reaction, U-235 absorbs a neutron and becomes U-236, which is unstable.

In one set of fusion reactions, the net reaction is that four protons combine to form a helium nucleus and two positrons.

Energy is released.

U-236 splits into two smaller nuclei, releasing energy and a few neutrons.

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27 SEP Construct Explanations Electric power plants that use nuclear fission reactions rely on a controlled self-sustaining chain reaction of splitting atoms. By examining the diagram for nuclear fission, explain how a chain reaction might occur. Explain why it is important to control the rate of the chain reaction.

ANCHORING

PHENOMENON

Revisit

GO ONLINE to Elaborate on and Evaluate your knowledge of mass conservation by completing the discussion and engineering design activities.

In the CER worksheet you completed at the beginning of the investigation, you constructed an explanation to answer a question about forest fires. With a partner, reevaluate the evidence you cited in your arguments.

28 SEP Construct Explanations Before the fire, the forest consists of large trees. After the fire, there is only ash. Interpret the chemical equation for the combustion reaction that takes place during a wildfire (C6H10O5 + 6O2 ⟶ 6CO2 + 5H2O) and explain what the law of conservation of mass suggests happened to the rest of the mass of the trees.

29 SEP Use Models Explain why understanding the process of combustion requires using an atomic model of mass and not a continuous one.

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Heat Transfer and Thermal Equilibrium

Heat Heat is not the same thing as thermal energy. Heat is not the same thing as temperature. In everyday language, the term heat is used in many different ways. In physical science, however, it refers only to the transfer of thermal energy from one object to another. Heat (Q, with units of joules or calories) is the energy that is moving from one object to another. The net result of interactions among atoms or other particles is that heat flows from hotter objects to colder objects. You can investigate the process of heat transfer that occurs in a system using calorimetry, the precise measurement of heat flow into or out of a system as a result of a chemical or physical process.

The flow of heat occurs in three ways: conduction, convection, and radiation. Conduction is the transfer of heat through or between physical objects in contact. Convection is the transfer of heat by fluid motions of the materials. Radiation is the transfer of heat through electromagnetic radiation. In many natural circumstances, all three mechanisms occur simultaneously. However, energy generally moves primarily by only one of the methods, depending on the circumstances.

Lava Lamp A lava lamp is a good example of the transfer of heat through all three mechanisms. A light shines into the bottom of a glass bottle containing two different types of liquid, one water-based and one oil-based.

30 SEP Construct Explanations Explain how heat in the lava lamp is being transferred by conduction, convection, and radiation.

EXPERIENCE 4

GO ONLINE to Explore and Explain the ways heat can be transferred from one place to another.

TEKS 13A,

13B, 13D

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Lower Temperature

Higher Temperature

Heat

Thermal Conduction For most materials other than metals, thermal conduction occurs through the oscillations of adjacent atoms. Atoms oscillate more actively when they are hotter. If hotter atoms are in contact with cooler atoms, there will be frequent collisions among them, and overall, energy will pass from the hotter to the cooler atoms.

Over time, with continued collisions, the energy will diffuse through a material or between adjacent materials. How efficiently heat is conducted through a material is measured as its thermal conductivity, k, in units of power per (length times temperature), W/(m·K). Thermal conduction through solids tends to be much faster than through liquids or gases because the distances between atoms in a solid are much less. Materials with very low thermal conductivities are called insulators.

Casting Metal Liquid metal is poured into a mold for it to cool. Heat immediately begins to flow into the walls of the mold.

Thermal Conduction at the Atomic Scale As a solid heats up, its atoms vibrate more energetically, and their collisions allow the heat to propagate through the material.

30 Investigation 1 Matter, Energy, and Change

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Heat

Warmer Cooler

Vibrating metal ions

Electrons

Conduction in Metals Thermal conduction in metals is a special case of conduction because the heat is carried by movements of the electrons as well as by movements of the atoms. The electrons at the highest energy levels dissociate from the atoms and drift through the metal. Electrons that are heated collide with and transfer heat to the vibrating atoms. Because of the high mobility of the electrons, the result is a rate of conduction that is much higher than from the atomic vibrations alone.

31 SEP Use Mathematics The heat flow through a material is directly proportional to the thermal conductivity of the material.

Suppose that a piece of polystyrene insulation board has a thermal conductivity that is 10,000 times less than that of copper. Use ratios to calculate how thick (in meters) a wall of copper has to be to provide the same heat insulation as a 4-cm polystyrene board.

Cooling Cup The metal spoon conducts heat much faster than the glass mug. The thermal conductivity of stainless steel (k = 16 W/(m·K)) is about twenty times higher than that of glass (k = 0.8 W/(m·K)).

Conduction electrons carry heat, and they also share it with atoms of the metal.

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Entropy and Thermodynamic Equilibrium How does entropy change as a system approaches equilibrium?

The molecules of the solid sugar cube are in a small volume of the beaker, and the system has low entropy.

As the sugar dissolves, the sugar molecules spread out, and entropy increases.

When the sugar is completely dissolved, the molecules are randomly distributed, and entropy is a maximum.

Entropy Entropy is a measure of the disorder of a system—the opposite of the order of the system. It is an important concept that describes the behavior of matter and energy within physical systems. In general, it is more likely for a physical system to be disordered than to be highly ordered.

The second law of thermodynamics states that the entropy of an isolated system never decreases. Therefore a system always spontaneously evolves toward the state with the maximum entropy, which is a state of thermodynamic equilibrium.

To give an everyday example, if a volume of gas is released into the corner of an empty room, it quickly becomes evenly distributed throughout the room. The system goes from a high-order, low-entropy state to a low-order, high-entropy state, which illustrates the second law of thermodynamics.