Chemistry
Energy Changes
Energy changes in chemistry refer to the transformation of energy from one form to another during chemical reactions. These changes can involve the release or absorption of energy, and are often measured in terms of heat. Understanding energy changes is crucial for predicting the feasibility and direction of chemical reactions, as well as for designing processes with specific energy requirements.
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12 Key excerpts on "Energy Changes"
eBook - PDFChemistry
The Molecular Nature of Matter
- James E. Brady, Neil D. Jespersen, Alison Hyslop(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
Thermochemistry is part of the science of thermodynamics, the study of energy trans- fer and energy transformation. Thermodynamics allows scientists to predict whether a proposed physical change or chemical reaction can occur under a given set of conditions. It is an essential part of chemistry (and all of the natural sciences). We’ll continue our study of thermodynamics in Chapter 19. LEARNING OBJECTIVES After reading this chapter, you should be able to: • explain the difference between potential and kinetic energy and the law of conservation of energy • explain the connection between temperature, energy, and the concept of a state function • determine an amount of heat exchanged from the temperature change of an object • describe the Energy Changes in exothermic and endothermic reactions • state the first law of thermodynamics and explain how it applies to chemistry • explain the difference between a heat of reaction obtained at constant pressure and the heat of reaction at constant volume • describe the assumptions and utility of thermochemical equations • use Hess's law to determine the enthalpy of a reaction • determine and use standard heats of formation to solve problems 6.1 | Energy: The Ability to Do Work 253 Potential energy (PE) is energy an object has that can be changed to kinetic energy; it can be thought of as stored energy. For example, when you wind an old style alarm clock, you transfer energy to a spring. The spring holds this stored energy (potential energy) and gradually releases it, in the form of kinetic energy, to make the clock’s mechanism work. Chemicals also possess potential energy, which is sometimes called chemical energy. When chemical reactions occur, the changes in chemical energy pos- sessed by the substances lead to either the absorption or release of energy (as heat or light, for instance).
eBook - PDF- Young, William Vining, Roberta Day, Beatrice Botch(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
Vasilyev/Shutterstock.com Thermochemistry Unit Outline 10.1 Energy 10.2 Enthalpy 10.3 Energy, Temperature Changes, and Changes of State 10.4 Enthalpy Changes and Chemical Reactions 10.5 Hess’s Law 10.6 Standard Heats of Reaction In This Unit… This unit begins an exploration of thermochemistry, the study of the role that energy in the form of heat plays in chemical processes. We inves-tigate the Energy Changes that take place during phase changes and the chemical reactions you have studied previously and learn why some chemical reactions occur while others do not. In Electromagnetic Radiation and the Electronic Structure of the Atom (Unit 3), you stud-ied Energy Changes at the molecular level and the consequences those Energy Changes have on the properties of atoms and elements. 10 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 Unit 10 Thermochemistry 272 10.1 Energy 10.1a Energy and Energy Units Chemical reactions involve reactants undergoing chemical change to form new substances, products. reactants S products What is not apparent in the preceding equation is the role of energy in a reaction. For many reactions, energy, often in the form of heat, is absorbed—that is, it acts somewhat like a reactant. You might write an equation for those reactions that looks like this: energy 1 reactants S products In other reactions, energy is produced—that is, it acts like a product: reactants S products 1 energy In Chemistry, Matter on the Atomic Scale (Unit 1), we defined energy (the ability to do work) and work (the force involved in moving an object some distance). From a chemist’s point of view, energy is best viewed as the ability to cause change, and thermochemistry is the study of how energy in the form of heat is involved in chemical change.
- Barron's Educational Series, Albert S. Tarendash(Authors)
- 2021(Publication Date)
- Barrons Educational Services(Publisher)
mechanical work. In this chapter, we will study more closely the concept of energy and its role in chemistry. First, we need to define some basic terms that will be used throughout the chapter.The part of the universe that a chemist chooses to study is called a system. The rest of the universe is known as the surroundings. For example, suppose you decide to study the melting of ice in a beaker, as shown in the accompanying diagram.The ice and water constitute the system; the beaker, the air, and everything else constitute the surroundings.In chemical processes, a system can interact with its surroundings in a number of ways, as shown in the following examples:- A beaker of liquid absorbs heat from a burner; in this example, energy is transferred between the system (the beaker of liquid) and its surroundings.
- A cylinder gas is compressed by a piston; in this example, work is done on the system (the gas) by its surroundings.
- Water is poured into a solution; in this example, mass has been transferred to the system (the solution) from its surroundings.
As we see from the examples given above, energy transfers involve transfers of heat and/or work. These transfers affect the total energy within a system, known as the internal energy (E), which has two main components: thermal energy, the energy associated with random molecular motions, and chemical energy, the energy associated with chemical bonds and attractions between the particles of a system.Since energy and work are so closely related, the same unit is used to measure both quantities. In the SI system, this unit is the joule (J); its multiple is the kilojoule (kJ). In this book, we will use the joule and the kilojoule exclusively.Heat
Heat is the energy transferred between a system and its surroundings as a result of a temperature difference. In the first example given above, heat passes from the burner to the beaker of liquid because the temperature of the burner is higher than the temperature of the beaker and liquid. Heat is represented by the symbol q. When energy is transferred into a system as a result of a temperature difference, heat is reported as a positive number, and we say that the process is endothermic; when energy is transferred out of a system as a result of a temperature difference, heat is reported as a negative number, and we say that the process is exothermic. For simplicity, we will state that in endothermic processes heat is absorbed, and in exothermic processes heat is released
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2015(Publication Date)
- Openstax(Publisher)
1. US Energy Information Administration, Primary Energy Consumption by Source and Sector, 2012, http://www.eia.gov/totalenergy/data/ monthly/pdf/flow/css_2012_energy.pdf. Data derived from US Energy Information Administration, Monthly Energy Review (January 2014). Chapter 5 | Thermochemistry 227 5.1 Energy Basics By the end of this section, you will be able to: • Define energy, distinguish types of energy, and describe the nature of Energy Changes that accompany chemical and physical changes • Distinguish the related properties of heat, thermal energy, and temperature • Define and distinguish specific heat and heat capacity, and describe the physical implications of both • Perform calculations involving heat, specific heat, and temperature change Chemical changes and their accompanying changes in energy are important parts of our everyday world (Figure 5.2). The macronutrients in food (proteins, fats, and carbohydrates) undergo metabolic reactions that provide the energy to keep our bodies functioning. We burn a variety of fuels (gasoline, natural gas, coal) to produce energy for transportation, heating, and the generation of electricity. Industrial chemical reactions use enormous amounts of energy to produce raw materials (such as iron and aluminum). Energy is then used to manufacture those raw materials into useful products, such as cars, skyscrapers, and bridges. Figure 5.2 The energy involved in chemical changes is important to our daily lives: (a) A cheeseburger for lunch provides the energy you need to get through the rest of the day; (b) the combustion of gasoline provides the energy that moves your car (and you) between home, work, and school; and (c) coke, a processed form of coal, provides the energy needed to convert iron ore into iron, which is essential for making many of the products we use daily.
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Thermochemistry is part of the science of thermodynamics, the study of energy transfer and energy transformation. Thermodynamics allows scientists to predict whether a proposed physical change or chem- ical reaction can occur under a given set of conditions. It is an essential part of chemistry (and all of the natural sciences). We’ll continue our study of thermodynamics in Chapter 18. CHAPTER OUTLINE 6.1 Energy: The Ability to Do Work 6.2 Heat, Temperature, and Internal Energy 6.3 Measuring Heat 6.4 Energy of Chemical Reactions 6.5 Heat, Work, and the First Law of Thermodynamics 6.6 Heats of Reaction 6.7 Thermochemical Equations 6.8 Hess’s Law 6.9 Standard Heats of Reaction Energy and Chemical Change David Willman/123 RF CHAPTER 6 260 CHAPTER 6 Energy and Chemical Change LEARNING OBJECTIVES After reading this chapter using your active reading skills, you should be able to: • explain the difference between potential and kinetic energy and explain the law of conservation of energy. • explain the connection between temperature, energy, and the concept of a state function. • determine the amount of heat exchanged from the temperature change of an object. • describe the Energy Changes in exothermic and endothermic reactions. • state the first law of thermodynamics and explain how it applies to chemistry. • explain the difference between the heat of reaction obtained at constant pressure and the heat of reaction at constant volume. • describe the assumptions and utility of thermochemical equations. • use Hess's law to determine the enthalpy of a reaction. • determine and use standard heats of formation to solve problems. CONNECTING TO THE LEARNING OBJECTIVES These suggestions are here to help you learn the chapter material. Writing notes while studying is known to be the best way to remember what you are studying.
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2019(Publication Date)
- Openstax(Publisher)
(credit: modification of work by Laszlo Ilyes) CHAPTER OUTLINE 1 US Energy Information Administration, Primary Energy Consumption by Source and Sector, 2012, http://www.eia.gov/totalenergy/ data/monthly/pdf/flow/css_2012_energy.pdf. Data derived from US Energy Information Administration, Monthly Energy Review (January 2014). 5.1 Energy Basics LEARNING OBJECTIVES By the end of this section, you will be able to: • Define energy, distinguish types of energy, and describe the nature of Energy Changes that accompany chemical and physical changes • Distinguish the related properties of heat, thermal energy, and temperature • Define and distinguish specific heat and heat capacity, and describe the physical implications of both • Perform calculations involving heat, specific heat, and temperature change Chemical changes and their accompanying changes in energy are important parts of our everyday world ( Figure 5.2). The macronutrients in food (proteins, fats, and carbohydrates) undergo metabolic reactions that provide the energy to keep our bodies functioning. We burn a variety of fuels (gasoline, natural gas, coal) to produce energy for transportation, heating, and the generation of electricity. Industrial chemical reactions use enormous amounts of energy to produce raw materials (such as iron and aluminum). Energy is then used to manufacture those raw materials into useful products, such as cars, skyscrapers, and bridges. FIGURE 5.2 The energy involved in chemical changes is important to our daily lives: (a) A cheeseburger for lunch provides the energy you need to get through the rest of the day; (b) the combustion of gasoline provides the energy that moves your car (and you) between home, work, and school; and (c) coke, a processed form of coal, provides the energy needed to convert iron ore into iron, which is essential for making many of the products we use daily.
eBook - PDFGeneral Chemistry I as a Second Language
Mastering the Fundamental Skills
- David R. Klein(Author)
- 2015(Publication Date)
- Wiley(Publisher)
133 CHAPTER 5 ENERGY AND ENTHALPY This chapter is the first part of a much larger topic called thermodynamics. You will revisit thermodynamics in more detail during the second semester of chemistry. The topics in this chapter will lay the foundation that you need for the second semester, so it is important to master the terms, concepts, and problem-solving techniques in this chapter. If you don’t get these topics down now, you will find yourself strug- gling with thermodynamics next semester. In one sentence, thermodynamics is the study of energy and its interconver- sions. Put more simply, thermodynamics is the study of how, why, and when en- ergy can be transferred from one place to another. In this chapter we focus on how energy is transferred. In the second semester of chemistry, you will learn about why and when energy is transferred (entropy and free energy). The first half of this chapter will focus on theory, terminology, and analogies. The second half of the chapter will focus on problem-solving techniques. 5.1 ENERGY We will start off our discussion with the different types of energy, but as we do so, keep in mind that we have still not defined what energy really is. We will get to the definition a bit later. Energy can be classified into the following categories: kinetic energy and po- tential energy. Kinetic energy is energy associated with motion (or velocity), and potential energy is energy associated with position. Let’s start with kinetic energy. When a soccer ball is in motion, it has kinetic energy (you might even remember the term 1 ⁄ 2 mv 2 from your high school physics class). When the soccer ball hits another ball, it will transfer some of its energy to the other ball. Molecules can do the same thing. A molecule in motion has kinetic energy that it can transfer when it collides with another molecule.
- Allan D. Kraus, James R. Welty, Abdul Aziz(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
3 Energy and the First Law of Thermodynamics Chapter Objectives • To describe the forms of energy and to define what is meant by kinetic, potential, internal, and total energy. • To define work and to show that it is not a property but a path function that depends on the path between two state points. • To define heat transfer and to show that it is not a property but a path function that depends on the path between two state points. • To present the concept of conservation of energy and to link all of the energy quantities considered into the first law of thermodynamics. • To consider thermodynamic cycles. • To develop the ideal gas model. • To consider enthalpy and specific heats for ideal gases. • To present the equations that govern three of the five fundamental processes of the ideal gas. 3.1 Introduction Energy may be defined as the capability or capacity to produce work. It is contained in all matter and while it exists in many different forms, these forms, however, are well defined. Because matter is anything that possesses mass and occupies space , energy is related to mass. Moreover, we may note that Einstein’s theory of relativity suggests that mass, m , may be converted to energy, E , (and energy may be converted to mass) via E = mc 2 where c = 2 . 9997 × 10 8 m/s is the speed of light. However, for all energy-mass interactions other than nuclear reactions, the amount of mass converted to energy is extremely small and can be neglected. Thus, in this study, we state the conservation of mass principle that is often quoted in subsequent discussions as Mass can neither be created nor destroyed and its composition cannot be altered from one form to another unless it undergoes a chemical change. 37 38 Introduction to Thermal and Fluid Engineering FORMS OF ENERGY Kinetic Energy is the energy that a body possesses by virtue of its motion. Potential Energy is the energy that a body possesses by virtue of its position.
eBook - PDF- John A. Olmsted, Gregory M. Williams, Robert C. Burk(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
SKILLS TO MASTER: Calculating energy and expansion work. Calculating the enthalpy change of a chemical reaction from standard enthalpies of formation. Calculating the enthalpy change of a chemical reaction under non-standard conditions. KEY CONCEPTS: Enthalpy is a thermodynamic state func- tion that describes heat flow at constant pressure. The heat transferred in a constant-pressure calorimeter is the enthalpy change. The heat transferred in a constant-volume calorimeter is the energy change. A formation reaction produces 1 mole of a chemical substance from the elements in their standard states. The enthalpy change for any overall process is equal to the sum of the enthalpy changes for any set of steps that leads from the starting materials to the products. 3.6 Energy Sources Coal Other renewables Hydro- electric Natural gas Nuclear Oil LEARNING OBJECTIVE: Be familiar with our sources of energy. Learning Exercises 3.1 List as many different types of energy as you can, and provide a specific example illustrating each energy type. 3.2 Write a paragraph that explains the relationships among energy, heat, work, and temperature. 3.3 Prepare a table listing all the bond energies involving halo- gen atoms (F, Cl, Br, I), organized so it matches the periodic table. What regularities can you find in this listing, and what exceptions are there? 3.4 Write a paragraph describing what happens to the energy released during a chemical reaction that occurs in a constant-pressure calorimeter. 3.5 Describe in your own words what enthalpy is and why it is preferred to energy in describing the thermochemistry of many chemical processes. 3.6 Make a list of energy sources that you personally use. For each item on your list, describe a way that you might be able to reduce your energy consumption. 3.7 Update your list of memory bank equations. Write a sentence that describes the restrictions on each equation.
eBook - PDF- Charles R. Russell(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER4 C H E M I C A L E N E R G Y INTRODUCTION Sufficient fuel has been stored by natural processes in coal, oil and gas reserves to meet most energy requirements at present. In addition, other chemical fuels such as hydrogen can be made to store energy for special purposes such as for rapid release of energy in a rocket motor. The chemical energy stored in a battery can be released in electrochemical reactions. Similar processes are utilized in fuel cells for direct energy conversion with high efficiency at moderate temperatures. Thus the chemical energy stored in fuels can be released by combustion to produce thermal energy for power generation or the chemical energy can be released by electrochemical processes directly yielding electrical energy. Chemical energy is a part of the potential internal energy of molecules, and is associated with molecular and atomic structure. Thermochemistry describes the Energy Changes accompanying chemical reactions. This science provides a systematic procedure for writing chemical equations including the changes in enthalpy and free energy. The thermochemistry of combustion and electro-chemical processes will be considered in this chapter. HEAT OF REACTION Chemical processes are accompanied by the release (exothermic reaction) or absorption (endothermic reaction) of energy usually as thermal energy. However, in electrochemical processes, electric-140 CHEMICAL ENERGY 141 al energy may be released or absorbed with only small thermal effects. Thermochemical equations include the chemical reaction and resulting changes in enthalpy or free energy for the reactants and products in their indicated states, as # 2 (g) + K> 2 (g) = H 2 0 (1) AH° = -68.317 kg-cal/g-mole Unless otherwise indicated, the reactants and products are at a pressure of one atmosphere and some standard temperature, T°, such as 298 °K.
eBook - ePubFoundations for Teaching Chemistry
Chemical Knowledge for Teaching
- Keith S. Taber(Author)
- 2019(Publication Date)
- Routledge(Publisher)
11 Energy and chemical changeChapter 10 explored the importance of energy as a concept in chemistry and recommended teaching about chemical bonding in terms of energy and the forces between charged particles. In this approach, strong chemical bonds such as covalent bonds and weaker interactions such as van der Waals’ forces are seen as having a similar underlying basis.This chapter looks at changes studied in chemistry, especially chemical reactions. However, if we model all types of bonding as based on the same underlying physical principles (primarily electromagnetic interactions), then we can also present students with a coherent perspective on how energy input can disrupt otherwise stable structures: not just in chemical reactions but in changes of state, atomisation (as used in mass spectroscopy), ionisation, and so forth.Energy input can disrupt otherwise stable structuresThe quanticles from which substances are composed, molecules or ions usually, have inherent energy (see Chapter 10 ), and if there is enough energy, bonding interactions can be disrupted – so in a liquid there is some degree of overcoming the bonding that was present in a solid (but by no means completely – e.g., see Chapter 8 ), and at the boiling temperature these quanticles have enough energy to move completely away from each other and overcome the bonding completely. (Again, this is a simplification – but a fair first approximation; in the vapour phase of some substances there will be some level of association of molecules or ions.)There are two important caveats here. Firstly, this is a description of a model that does not tell the whole story – a recurrent theme in chemistry. In an ideal gas the molecules can be considered as completely independent, but that assumes the molecules are always so far apart that the forces between them are effectively zero. Of course, sometimes the molecules will get very close. We can imagine what happens when two molecules have a ‘near miss’, and come close enough to almost collide as they pass each other. For a short period, the forces between these fuzzy balls of charge will be attracting them together. If the gas cools and the particles are no longer moving fast enough to escape these attractions, condensation occurs.
eBook - PDF- Richard L. Myers(Author)
- 2005(Publication Date)
- Greenwood(Publisher)
H Work, Energy, and Heat Introduction Life requires a continual input of energy into the Earth. This energy is distributed over the Earth by wind and water currents. Our ancestors learned how to harness these forms of energy to perform work. The rig- ging of a sail on a boat or the use of a water- mill to grind wheat are simple examples of how energy is transformed into work. Modern society primarily depends on the chemical energy locked inside fossils fuels for its energy. Energy is required to support a high standard of living, and the develop- ment of an industrial society depends on an adequate supply of energy. Because of this, energy is often examined as it relates to politics, the environment, and technol- ogy. We use the terms work, energy, and heat every day, but they have very specific meanings in the context of physics. When someone says they are going to work or to turn up the heat, we know exactly what is meant. Problems can arise, though, when we try to relate the colloquial meanings of these terms to their physical meaning. This chapter will focus on the scientific meaning of work and energy and introduce how heat relates to these two concepts. Heat and how it affects matter will be more fully explored in the next chapter. System and Surroundings In order to examine work, energy, and heat it is helpful to define a system to which these concepts apply. A system is that part of the universe a person is interested in and wants to examine. The concept of a system often seems abstract and arbitrary. At times it is very easy to define a system, while in other cases it might not be obvious what the system includes. For example, when you take an ice cube out of the freezer and place it in a glass at room temperature, the system can be defined as the glass and its contents. In addi- tion to the glass, the system includes the ice cube, liquid water as the ice cube melts, and the air in the glass.
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