Chemistry
Chemical Equilibrium
Chemical equilibrium is a state in a chemical reaction where the forward and reverse reactions occur at the same rate, resulting in no net change in the concentrations of reactants and products. At equilibrium, the concentrations of reactants and products remain constant, but the reactions continue to occur. This dynamic balance is described by the equilibrium constant.
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11 Key excerpts on "Chemical Equilibrium"
eBook - PDF- Ageetha Vanamudan(Author)
- 2023(Publication Date)
- Delve Publishing(Publisher)
The system’s temperature, pressure, and concentration can all affect how the equilibrium is maintained. For instance, if even a single one of these components is altered, the equilibrium of the system will be thrown off, and the system will need to adjust to reach its former condition. In this and the next sections, we will cover some of the most essential elements that influence equilibrium. 12.3 THE CHEMISTRY BEHIND REACHING AN EQUILIBRIUM A system is regarded to be in Chemical Equilibrium when the concentrations of the reactant and product do not vary over time and the characteristics of the system do not change in any manner. Another evidence of this condition is that there is no obvious change in the system’s properties. The system is deemed to be in a condition of equilibrium so long as the forward and backward reactions continue to move at the same speed. The state of equilibrium is obtained when the rate of the reaction moving forward is similar to the rate of the reaction going backwards. As a consequence of this, the term is typically used to define a system in which the concentrations of both the reactant and the product are maintained throughout the experiment (Dufrêne et al., 2017). When there is no longer any change in the system’s properties, the system will have achieved its fixed state. It is stated that the concentrations of the reactants and products have reached a condition of dynamic equilibrium when the forward and reverse processes utilize rates that are similar to one another. Chemical Equilibrium 207 12.4 THE FACTORS THAT AFFECT EQUILIBRIUM Figure 12.4: The Factors That Affect Equilibrium.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
A double arrow is used in the equation to indicate that the reaction is reversible. Any system at equilibrium represents a dynamic state in which two or more opposing processes are taking place at the same time and at the same rate. A Chemical Equilibrium is a dynamic system in which two or more opposing chemical reactions are going on at the same time and at the same rate. When the rate of the forward reaction is exactly equal to the rate of the reverse reaction, a condition of Chemical Equilibrium exists (see purple line in KEY TERMS reversible chemical reaction equilibrium Chemical Equilibrium NO 2 Figure 16.2 Reversible reaction of NO 2 and N 2 O 4 . More of the dark brown molecules are visible in the heated container on the right than in the room-temperature tube on the left. LEARNING OBJECTIVE N 2 O 4 Richard Megna/Fundamental Photographs Richard Megna/Fundamental Photographs 366 CHAPTER 16 • Chemical Equilibrium P R A C T I C E 1 6 . 2 What symbolism is used in a chemical equation to indicate that a chemical reaction is reversible? Figure 16.1). The concentrations of the products and the reactants are not changing, and the system appears to be at a standstill because the products are reacting at the same rate at which they are being formed. Chemical Equilibrium: rate of forward reaction = rate of reverse reaction A saturated salt solution is in a condition of equilibrium: NaCl(s) m Na + (aq) + Cl - (aq) At equilibrium, salt crystals are continuously dissolving, and Na + and Cl - ions are continu- ously crystallizing. Both processes are occurring at the same rate. The ionization of weak electrolytes is another Chemical Equilibrium system: HC 2 H 3 O 2 (aq) + H 2 O(l) m H 3 O + (aq) + C 2 H 3 O 2 - (aq) In this reaction, the equilibrium is established in a 1 M solution when the forward reaction has gone about 1%—that is, when only 1% of the acetic acid molecules in solution have ionized.
eBook - PDF- Morris Hein, Susan Arena, Cary Willard(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
EXAMPLE 16.2 Is a reversible chemical reaction at equilibrium a static or a dynamic system? Explain. SOLUTION A reversible chemical reaction is a dynamic system in which two opposing reactions are taking place at the same time and at the same rate of reaction. P R A C T I C E 1 6 . 2 What symbolism is used in a chemical equation to indicate that a chemical reaction is reversible? 372 CHAPTER 16 • Chemical Equilibrium 16.3 Le Châtelier’s Principle Use Le Châtelier’s principle to predict the changes that occur when concentration, temperature, or volume is changed in a system at equilibrium. In 1888, the French chemist Henri Le Châtelier (1850–1936) set forth a simple, far- reaching generalization on the behavior of equilibrium systems. This generalization, known as Le Châtelier’s principle, states: If a stress is applied to a system in equilibrium, the system will respond in such a way as to relieve that stress and restore equilibrium under a new set of conditions. The application of Le Châtelier’s principle helps us predict the effect of changing con- ditions in chemical reactions. We will examine the effect of changes in concentration, temperature, and volume. Effect of Concentration on Equilibrium The manner in which the rate of a chemical reaction depends on the concentration of the reactants must be determined experimentally. Many simple, one-step reactions result from a collision between two molecules or ions. The rate of such one-step reactions can be altered by changing the concentration of the reactants or products. An increase in concentration of the reactants provides more individual reacting species for collisions and results in an increase in the rate of reaction. An equilibrium is disturbed when the concentration of one or more of its components is changed. As a result, the concentration of all species will change, and a new equilibrium mix- ture will be established.
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Chapter 5 GENERAL CONCEPTS OF Chemical Equilibrium “The worst form of inequality is to try to make unequal things equal.” —Aristotle KEY THINGS TO LEARN FROM THIS CHAPTER The equilibrium constant (key Equations: 5.12, 5.15) Calculation of equilibrium concentrations Using Excel Goal Seek to solve one-variable equations The systematic approach to equilibrium calculations: mass balance and charge balance equations Activity and activity coefficients (key Equation: 5.19) Thermodynamic equilibrium constants (key Equation: 5.23) Even though in a chemical reaction the reactants may almost quantitatively react to form the products, reactions never go in only one direction. In fact, reactions reach an equilibrium in which the rates of reactions in both directions are equal. In this chapter we review the equilibrium concept and the equilibrium constant and describe gen- eral approaches for calculations using equilibrium constants. We discuss the activity of ionic species along with the calculation of activity coefficients. These values are required for calculations using thermodynamic equilibrium constants, that is, for the diverse ion effect, described at the end of the chapter. They are also used in potentio- metric calculations (Chapter 20). 5.1 Chemical Reactions: The Rate Concept In 1863 Guldberg and Waage described what we now call the law of mass action, which states that the rate of a chemical reaction is proportional to the “active masses” of the reacting substances present at any time. The active masses may be concentrations or pressures. Guldberg and Waage derived an equilibrium constant by defining equilib- rium as the condition when the rates of the forward and reverse reactions are equal.
eBook - PDF- Gary D. Christian, Purnendu K. Dasgupta, Kevin A. Schug(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
Chapter Six GENERAL CONCEPTS OF Chemical Equilibrium “The worst form of inequality is to try to make unequal things equal.” — Aristotle Learning Objectives WHAT ARE SOME OF THE KEY THINGS WE WILL LEARN FROM THIS CHAPTER? ● The equilibrium constant (key equations: 6.12, 6.15), pp. 194 ● Calculation of equilibrium concentrations, p. 195 ● Using Excel Goal Seek to solve one-variable equations, p. 197 ● The systematic approach to equilibrium calculations: mass balance and charge balance equations, p. 204 ● Activity and activity coefficients (key equation: 6.19), p. 211 ● Thermodynamic equilibrium constants (key equation: 6.23), p. 217 Even though in a chemical reaction the reactants may almost quantitatively react to form the products, reactions never go in only one direction. In fact, reactions reach an equilibrium in which the rates of reactions in both directions are equal. In this chapter we review the equilibrium concept and the equilibrium constant and describe general approaches for calculations using equilibrium constants. We discuss the activity of ionic species along with the calculation of activity coefficients. These values are required for calculations using thermodynamic equilibrium constants, that is, for the diverse ion effect, described at the end of the chapter. They are also used in potentiometric calculations (Chapter 13). 6.1 Chemical Reactions: The Rate Concept In 1863 Guldberg and Waage described what we now call the law of mass action, which states that the rate of a chemical reaction is proportional to the “active masses” of the reacting substances present at any time. The active masses may be concentrations or pressures. Guldberg and Waage derived an equilibrium constant by defining equilibrium as the condition when the rates of the forward and reverse reactions are equal.
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
Chapter 7Chemical Equilibrium
Abstract
This chapter reviews the principles of Chemical Equilibrium beginning with the concept that many chemical reactions are reversible. These reversible reactions achieve a dynamic equilibrium where the rate of the forward reaction equals the rate of the reverse reaction. This dynamic equilibrium is described by an equilibrium constant, which is determined from the concentrations of the reactants and products at equilibrium. The magnitude of the equilibrium constant is presented as measure of the extent that the forward and reverse reactions take place. Le Chatelier's principle is introduced and the changes in reaction conditions that can disturb a Chemical Equilibrium are reviewed. The response of the chemical reaction to these changes in reaction conditions is explained in detail. The reaction quotient is presented as a means of determining the direction the reaction is likely to proceed.Keywords
Reversible reactions; Dynamic equilibrium; Equilibrium constant; Partial pressures; Le Chatelier's principle; Exothermic; Endothermic; Reaction quotientOutline7.1Reversible Reactions7.2The Equilibrium Constant7.3Relationships Between Equilibrium Constants7.4Le Chatelier's Principle: Disturbing a Chemical Equilibrium7.5The Reaction QuotientImportant TermsStudy QuestionsProblems7.1 Reversible Reactions
The idea that a chemical reaction can be reversible was introduced by Claude Louis Berthollet in 1803 when he observed the formation of sodium carbonate crystals at the edge of a limestone salt lake in Egypt (Fig. 7.1 ). Since the salt lake was a landlocked body of water with a very high concentration of dissolved sodium chloride (> 3 g/L) and other minerals, he knew that the formation of these crystals must be a result of the following chemical reaction;Fig. 7.1
- Noel de Nevers(Author)
- 2012(Publication Date)
- Wiley(Publisher)
Chapter 12 Chemical Equilibrium12.1 Introduction to Chemical Reactions and Chemical EquilibriumChemical reactions transform one chemical species or set of species to another species or set of species: reactant(s) → product(s). Sometimes we do this because the products (e.g., pharmaceuticals) are much more valuable than the reactants from which they are made. Sometimes we want the heat released by the chemical reaction of the materials (e.g., fuels) with air (burning) either to heat some material (cooking our food or heating our homes) or to burn the fuels inside the engines that propel our vehicles or generate electricity. Sometimes we destroy harmful materials by chemical reaction (incineration of hazardous hydrocarbons, destruction of bacteria, protozoa, and viruses in drinking water with chlorine or ozone). The most important chemical reactions are those within our bodies. Every second millions of chemical reactions are occurring in our bodies, accomplishing all the things we call life. The chemical reactions in our nervous system control our muscular movements and our thoughts; the nerve gases that interfere with those chemical reactions can kill in seconds.In this chapter we consider only single chemical reactions, all occurring in one phase. In the next chapter we consider multiple reactions, in series and in parallel, occurring in one or more phases. The next chapter introduces no new principles, only more complex and interesting applications of the ideas of this chapter.
eBook - PDFChemistry
An Atoms First Approach
- Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste, , Steven Zumdahl, Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. For Review Key Terms Chemical Equilibrium Section 12.2 law of mass action equilibrium expression equilibrium constant equilibrium position Section 12.4 homogeneous equilibria heterogeneous equilibria Section 12.5 reaction quotient (Q) Section 12.7 Le Châtelier’s principle Chemical Equilibrium ❯ When a reaction takes place in a closed system, it reaches a condition where the concentra- tions of the reactants and products remain constant over time ❯ Dynamic state: reactants and products are interconverted continually ❯ Forward rate 5 reverse rate ❯ The law of mass action: for the reaction jA 1 kB m mC 1 nD K 5 fCg m fDg n fAg j fBg k 5 equilibrium constant ❯ A pure liquid or solid is never included in the equilibrium expression ❯ For a gas-phase reaction, the reactants and products can be described in terms of their partial pressures and the equilibrium constant is called K p : K p 5 KsRTd Dn where Dn is the sum of the coefficients of the gaseous products minus the sum of the coef- ficients of the gaseous reactants Equilibrium Position ❯ A set of reactant and product concentrations that satisfies the equilibrium constant expression ❯ There is one value of K for a given system at a given temperature ❯ There are an infinite number of equilibrium positions at a given temperature depending on the initial concentrations ❯ A small value of K means the equilibrium lies to the left; a large value of K means the equi- librium lies to the right ❯ The size of K has no relationship to the speed at which equilibrium is achieved ❯ Q, the reaction quotient, applies the law of mass action to initial concentrations rather than equilibrium concentrations ❯ If Q .
eBook - PDFChemistry
An Industry-Based Introduction with CD-ROM
- John Kenkel, Paul B. Kelter, David S. Hage(Authors)
- 2000(Publication Date)
- CRC Press(Publisher)
287 11 Chemical Equilibrium 11.1 Introduction ................................................................... 287 11.2 Chemical Equilibrium ................................................... 289 11.3 Important Examples of Chemical Equilibrium ........... 290 11.4 The Equilibrium Constant ............................................ 291 11.5 The Maganitude of the Equilibrium Constant ............ 293 11.6 Le Châtelier’s Principle .................................................. 294 11.7 Effect of Concentration Change ................................... 294 11.8 Effect of Temperature Change ...................................... 295 11.9 Effect of Pressure Change ............................................. 297 11.10 Effect of Catalysts .......................................................... 298 11.11 Equilibrium Calculations .............................................. 298 How Much Exists in Solution • Modifying the Amount that Dissolves • Calculations Involving K a and K b 11.12 Homework Exercises ...................................................... 306 11.1 Introduction Consider an experiment in which all the students in your class line up against the walls of the classroom, half on one side and half on the other. Then consider what would happen when one student on each side walks to the opposite side at exactly the same speed, passing each other in the middle. As soon as each of these students arrives at the other side, another student walks back to the opposite side, continuing at the same speed. Now imagine continuing this process indefinitely. It would be a very dynamic process, two students always moving from one side to the other in opposite directions, but there would never be any net change in the count of students on each side. If we were unable to see the students walking and were only able to count the number of students in the lines, we would never know that anything was happening.
eBook - PDFIntroductory Chemistry
An Active Learning Approach
- Mark Cracolice, Edward Peters, Mark Cracolice(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
P/Review The development of a liquid–vapor pressure equilibrium is described in Section 15.5. An equilibrium between excess solute and a saturated solution is examined in Section 16.4. Both equilibria involve physical changes in which one of the two opposing rates remains constant until the other catches up with it. Here we study how a Chemical Equilibrium develops. This time, both forward and reverse rates change as equilibrium is reached. Time 1 2 F 0 F 1 F 2 F E = R E R 2 R 1 R 0 Reaction rate Figure 18.10 Changes in reaction rates during the development of a Chemical Equilibrium. The forward rate is represented by the upper curve in red, and the reverse rate is shown by the lower curve in blue. Figure 18.11 Henry Louis Le Chatelier (1850–1936). In addition to being a talented scientist, Le Chate- lier was an educational reformer and an excellent teacher. Oesper Collection in the History of Chemistry, University of Cincinnati Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 709 18.7 Le Chatelier’s Principle The Concentration Effect Goal 8 Given the equation for a Chemical Equilibrium, or information from which it can be written, predict the direction in which the equilibrium will shift because of a change in the concentration of one species. The reaction of hydrogen and iodine to produce hydrogen iodide comes to equi- librium with hydrogen iodide as the favored species—that is, the species having the higher concentration.
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
For a given overall chemical composition, the amounts of reactants and products that are present at equilibrium are the same regardless of whether the equilibrium is approached from the direction of pure “reactants,” pure “products,” or any mixture of them. Explain the basics of equilibrium laws The mass action expression is a fraction. The concentrations of the products, raised to powers equal to their coefficients in the chemical equation for a homogeneous equilibrium, are multi- plied together in the numerator. The denominator is con- structed in the same way from the concentrations of the reactants raised to powers equal to their coefficients. The numerical value of the mass action expression is the reaction quotient, Q. At equilibrium, the reaction quotient is equal to the equilibrium constant, K c . If partial pressures of gases are used in the mass action expression, is represented as K P . The magnitude of the equilibrium constant is roughly proportional to the extent to which the reaction proceeds to completion when equilibrium is reached. Equilibrium equations can be manipulated by multiplying the coefficients by a common fac- tor, changing the direction of the reaction, and by adding two or more equilibria. The rules given in the description of the Tools for Problem Solving below apply. Write and convert between equilibrium laws based on molar concentration and gas pressures The values of K P and K c are only equal if the same number of moles of gas are represented on both sides of the chemical equa- tion. When the numbers of moles of gas are different, K P is related to K c by the equation K P = K c (RT) n g . Remember to use R = 0.0821 L atm mol -1 K -1 and T = absolute temperature. Also, be careful to calculate ∆n g as the difference between the number of moles of gaseous products and the number of moles of gaseous reactants in the balanced equation.
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