13.2 Equilibrium Constants
3 min read•june 25, 2024
is a dynamic state where forward and reverse reactions occur at equal rates. Equilibrium constants quantify this balance, revealing whether products or reactants are favored at equilibrium. Understanding these constants helps predict reaction outcomes and their relationship to .
Reaction quotients compare current concentrations to equilibrium values, guiding reactions towards balance. Equilibrium constants, calculated from equilibrium concentrations, indicate reaction extent and spontaneity. Their magnitude reveals whether products or reactants dominate, connecting , thermodynamics, and reaction mechanisms.
Equilibrium Constants
Reaction quotients for chemical reactions
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- () compares current concentrations or partial pressures of reactants and products to determine the direction a reaction will proceed to reach equilibrium
- For the general reaction , the reaction quotient is calculated as
- In homogeneous reactions, reactants and products are in the same phase
- For gaseous reactions, partial pressures are used instead of concentrations in the reaction quotient ()
- involve reactants and products in different phases
- Solids and pure liquids have constant concentrations and are excluded from the reaction quotient
- Only gaseous and aqueous species are included in the reaction quotient
Calculation of equilibrium constants
- () is the value of the reaction quotient at equilibrium, calculated using equilibrium concentrations or partial pressures
- For the general reaction , the equilibrium constant based on concentrations is
- The equilibrium constant based on partial pressures is
- and are related by , where moles of gaseous products - moles of gaseous reactants, is the gas constant (0.08206 L mol K), and is the in Kelvin
- Equilibrium constants are temperature-dependent, and changing the temperature shifts the and alters the equilibrium constant
- plays a crucial role in determining the equilibrium constant, as the coefficients in the balanced chemical equation are used as exponents in the equilibrium constant expression
Significance of equilibrium constant values
- The magnitude of the equilibrium constant indicates the extent of the reaction at equilibrium
- Large values () suggest the reaction favors products at equilibrium (product-favored)
- Small values () suggest the reaction favors reactants at equilibrium (reactant-favored)
- suggests the reaction reaches equilibrium with significant amounts of both reactants and products
- The equilibrium constant is related to the change () of the reaction by
- Negative values correspond to (spontaneous reaction)
- Positive values correspond to (non-spontaneous reaction)
- Equilibrium constants can predict the direction of a reaction
- If , the reaction proceeds to the right (towards products) to reach equilibrium
- If , the reaction proceeds to the left (towards reactants) to reach equilibrium
- If , the reaction is at equilibrium, and no net change occurs
Relationship between Equilibrium, Kinetics, and Thermodynamics
- Equilibrium is related to both kinetics and thermodynamics of a chemical reaction
- Kinetics describes the rate at which a reaction approaches equilibrium, often expressed through rate laws
- Thermodynamics determines the final equilibrium position and the value of the equilibrium constant
- The , which describes the step-by-step process of a chemical reaction, influences both the kinetics and the overall equilibrium of the system
Key Terms to Review (46)
Aqueous solution: An aqueous solution is a solution in which water is the solvent. Commonly used in chemistry to describe reactions occurring in water.
Atm: The abbreviation 'atm' stands for 'atmosphere', which is a unit of pressure measurement commonly used in the context of gases. It represents the average pressure exerted by the Earth's atmosphere at sea level and is a fundamental concept in understanding the behavior of gases, particularly in the topics of effusion, diffusion, and equilibrium constants.
Atmosphere (atm): Atmosphere (atm) is a unit of pressure defined as 101,325 Pa. It represents the average pressure exerted by Earth's atmosphere at sea level.
Chemical Equilibrium: Chemical equilibrium is a state where the forward and reverse reactions in a chemical system occur at equal rates, resulting in no net change in the concentrations of the reactants and products over time. This dynamic balance is a fundamental concept in understanding the behavior of chemical systems.
Chemical thermodynamics: Chemical thermodynamics studies the interrelation of heat and work with chemical reactions or physical changes. It applies principles of thermodynamics to predict the direction and extent of chemical processes.
Concentration: Concentration is the measure of the amount of a solute that is dissolved in a given quantity of solvent. It is commonly expressed in terms of molarity (M), which is moles of solute per liter of solution.
Concentration: Concentration is a measure of the amount of a substance present in a given volume or mass of a solution or mixture. It is a fundamental concept in chemistry that is closely related to the study of chemical reactions, equilibrium, and the behavior of solutions.
Dalton’s law of partial pressures: Dalton's law of partial pressures states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of each individual gas. Each gas in a mixture behaves independently and contributes to the total pressure in proportion to its mole fraction.
Dynamic equilibrium: Dynamic equilibrium occurs when the rates of the forward and reverse processes are equal, resulting in no net change in the system. It is a key concept in phase transitions where phases coexist at equilibrium.
Dynamic Equilibrium: Dynamic equilibrium is a state in which opposing chemical processes occur at equal rates, resulting in a stable and unchanging overall system. It is a fundamental concept in chemistry that describes the balance between forward and reverse reactions in a closed system.
Equilibrium Constant: The equilibrium constant is a quantitative measure of the extent of a chemical reaction at equilibrium. It represents the ratio of the concentrations of the products to the reactants, raised to their respective stoichiometric coefficients, and is a fundamental concept in understanding the behavior of chemical systems at equilibrium.
Equilibrium constant, K: The equilibrium constant, $K$, is a ratio that quantifies the concentrations of reactants and products in a chemical reaction at equilibrium. It provides insight into the position of the equilibrium and the extent to which reactants are converted into products.
Equilibrium Position: Equilibrium position refers to the state in which the forward and reverse reactions in a chemical system occur at equal rates, resulting in a constant composition of the reactants and products. This term is central to understanding the behavior and characteristics of chemical equilibria.
Gibbs Free Energy: Gibbs free energy is a thermodynamic property that combines the concepts of enthalpy and entropy to determine the spontaneity and feasibility of a chemical process. It is a crucial factor in understanding the driving forces behind chemical reactions and phase changes.
Gibbs free energy (G): Gibbs free energy (G) is a thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure. It is used to predict the direction of chemical reactions.
Guldberg: Cato Maximilian Guldberg was a Norwegian mathematician and chemist who, along with his colleague Peter Waage, developed the law of mass action, which is a fundamental principle in chemical equilibrium. Guldberg's work on equilibrium constants and the relationship between reactant concentrations and reaction rates laid the foundation for our understanding of chemical equilibrium processes.
Heterogeneous Reactions: Heterogeneous reactions are chemical reactions that occur between substances in different physical states, such as a solid and a gas or a liquid and a gas. These reactions involve the interaction of reactants at the interface between the phases, and the reaction rate is often influenced by factors like surface area, diffusion, and adsorption.
Homogeneous equilibrium: Homogeneous equilibrium occurs when all reactants and products of a chemical reaction are in the same phase, usually liquid or gas. It is characterized by a constant ratio of the concentrations of reactants and products at equilibrium.
Homogeneous Equilibrium: A homogeneous equilibrium is a state of balance in a chemical system where the concentrations of all reactants and products remain constant over time, and the system is composed of a single phase, such as a gas or a solution. This term is crucial in understanding the principles of chemical equilibria, equilibrium constants, and equilibrium calculations.
Integrated rate laws: Integrated rate laws describe the concentration of reactants as a function of time. They are derived from differential rate laws and are used to determine reaction order and rate constants.
K: K is a variable used to represent various constants and parameters in the context of chemical processes and principles. It is a versatile term that appears in multiple areas of chemistry, including the study of gas behavior, reaction kinetics, chemical equilibrium, and thermodynamics.
Kc: Kc, or the equilibrium constant, is a quantitative measure of the extent of a chemical reaction at equilibrium. It represents the ratio of the concentrations of the products to the concentrations of the reactants, raised to their respective stoichiometric coefficients. The value of Kc provides insight into the position of the equilibrium and the relative amounts of products and reactants present at equilibrium.
Kinetics: Kinetics is the study of the rates of chemical reactions and the factors that influence those rates. It is a fundamental aspect of chemistry that examines how quickly reactants are converted into products, providing insights into the mechanisms and pathways of chemical transformations.
Kp: Kp, also known as the equilibrium constant for partial pressures, is a measure of the relative concentrations of reactants and products at equilibrium in a chemical reaction. It is a fundamental concept in the study of chemical equilibria and is used to predict the direction and extent of a reaction under specific conditions.
Law of mass action: The law of mass action states that the rate of a chemical reaction is directly proportional to the product of the concentrations of the reactants, each raised to a power equal to its coefficient in the balanced chemical equation. It is fundamental in deriving equilibrium constants.
Law of Mass Action: The law of mass action is a fundamental principle in chemical kinetics that describes the relationship between the rates of chemical reactions and the concentrations of the reactants. It states that the rate of a chemical reaction is proportional to the product of the concentrations of the reactants, raised to the power of their stoichiometric coefficients.
Le Chatelier's Principle: Le Chatelier's Principle states that when a system at equilibrium is subjected to a change in one of the conditions (concentration, temperature, or pressure) affecting that equilibrium, the system will shift to counteract the change and re-establish equilibrium.
Mol/L: Mol/L, also known as molarity, is a measure of the concentration of a substance in a solution. It represents the number of moles of a solute dissolved in one liter of the solution. Molarity is a fundamental concept in chemistry that is essential for understanding chemical reactions, equilibrium, and precipitation processes.
Pressure: Pressure is a measure of the force exerted per unit area on a surface or object. It is a fundamental concept in physics and chemistry that plays a crucial role in understanding the behavior of gases, liquids, and solids, as well as the principles of equilibrium and the shifting of equilibria.
Q: Q, also known as the equilibrium constant, is a measure of the relative concentrations of reactants and products at equilibrium in a chemical reaction. It is a fundamental concept in understanding the behavior of chemical systems and is essential in the study of equilibrium constants, equilibrium calculations, and precipitation and dissolution processes.
Qp: Qp, also known as the reaction quotient, is a mathematical expression that describes the relative concentrations of reactants and products in a chemical equilibrium system. It is a key concept in understanding the behavior and direction of chemical reactions at equilibrium.
Rate Law: The rate law is an equation that describes the relationship between the rate of a chemical reaction and the concentrations of the reactants. It is a fundamental concept in chemical kinetics that helps quantify and predict the speed of a reaction under specific conditions.
Reaction mechanism: A reaction mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. It provides detailed information on the intermediates, transition states, and energy changes throughout the process.
Reaction Mechanism: A reaction mechanism is the step-by-step sequence of elementary reactions that describes how reactants are transformed into products during a chemical reaction. It provides a detailed understanding of the pathways and intermediates involved in the overall chemical process.
Reaction Quotient: The reaction quotient, denoted as Q, is a measure of the relative concentrations of the products and reactants in a chemical reaction at any given time, regardless of whether the system has reached equilibrium or not. It is a useful tool for understanding the direction and extent of a reaction as it progresses towards equilibrium.
Reaction quotient (Q): The reaction quotient, Q, is a measure of the relative amounts of products and reactants present in a reaction mixture at any given point in time. It is calculated using the same expression as the equilibrium constant but with current concentrations or partial pressures.
Reversible Reaction: A reversible reaction is a chemical reaction in which the products can react to form the original reactants. In other words, the reaction can proceed in both the forward and reverse directions, reaching a state of dynamic equilibrium.
Reversible reactions: Reversible reactions are chemical reactions where the reactants form products that can react together to reform the reactants. These reactions can proceed in both forward and reverse directions.
Standard free energy changes, ΔG°: Standard free energy change, $\Delta G^\circ$, is the change in Gibbs free energy for a reaction under standard conditions (1 bar, 298 K, and 1 M concentration). It indicates whether a reaction is spontaneous under these conditions.
Standard temperature and pressure (STP): Standard Temperature and Pressure (STP) is a reference point used in chemistry to define a set of conditions for experimental measurements. It is defined as a temperature of 0°C (273.15 K) and a pressure of 1 atm.
Steady State: The steady state is a condition where the concentrations of reactants and products in a chemical system remain constant over time, despite the ongoing chemical reactions. This term is particularly relevant in the context of chemical equilibria and equilibrium constants.
Stoichiometry: Stoichiometry is the calculation of reactants and products in chemical reactions using balanced chemical equations. It involves the use of molar ratios derived from these equations to predict quantities of substances consumed and produced.
Temperature: Temperature is a measure of the average kinetic energy of the particles (atoms or molecules) in a substance. It is a fundamental physical quantity that reflects the degree of hotness or coldness of an object or system, and it plays a crucial role in various chemical and physical processes.
Thermodynamics: Thermodynamics is the branch of physics that deals with the relationships between heat, work, temperature, and energy. It describes the fundamental physical laws governing the transformation of energy and the flow of heat, which are essential to understanding the behavior of chemical systems and processes.
Waage: The Waage, also known as the equilibrium constant, is a fundamental concept in chemistry that quantifies the balance between the reactants and products in a chemical reaction at equilibrium. It is a measure of the relative concentrations of the reactants and products at the point where the forward and reverse reactions occur at the same rate, indicating a state of dynamic equilibrium.
ΔG°: ΔG° is the standard Gibbs free energy change, which represents the maximum amount of useful work that can be extracted from a spontaneous chemical reaction under standard conditions. It is a fundamental concept in chemical equilibria and the determination of equilibrium constants.