13.1 Chemical Equilibria
3 min read•june 25, 2024
Chemical is a delicate balance in reactions. When forward and reverse rates equalize, concentrations stabilize. This dynamic state is achieved when the system's energy is minimized, influenced by factors like temperature and .
At , molecules constantly interchange between reactants and products. The system maintains stability unless disturbed. Understanding equilibrium helps predict reaction outcomes and manipulate conditions for desired results in various chemical processes.
Chemical Equilibrium
Reaching chemical equilibrium
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- Chemical reactions reach equilibrium when forward and reverse reaction rates equalize
- At equilibrium, reactant and product concentrations remain constant over time
- System is in a state of with no net change in concentrations
- Equilibrium state is reached when () of the system minimizes
- () relates to standard Gibbs free energy change () by equation:
- Factors affecting time to reach equilibrium:
- Temperature: Higher temperatures generally accelerate reaction rates and equilibrium attainment (boiling water)
- Concentration of reactants and products: Higher concentrations can speed up reaction rates and equilibrium attainment (carbonated beverages)
- Presence of a : Catalysts reduce activation energy, increasing reaction rates and decreasing time to reach equilibrium (enzymes in biological systems)
Dynamic nature of equilibrium
- At equilibrium, forward and reverse reactions occur at equal rates
- Reactants constantly convert to products, and products constantly convert back to reactants
- Reactant and product concentrations remain constant, but individual molecules continuously interchange (evaporation and condensation of water in a closed container)
- Equilibrium state maintains as long as system remains undisturbed by external factors
- Changes in temperature, pressure, or concentration can shift (adding ice to a glass of water)
- describes how equilibrium systems respond to disturbances
- When stress is applied to a system at equilibrium, the system adjusts to minimize the stress effect and re-establish equilibrium (increasing pressure on a gas-phase reaction)
- Stresses include changes in concentration, pressure, volume, or temperature (removing product from a reaction mixture)
Calculating equilibrium concentrations
- Equilibrium constant () is the ratio of product of equilibrium concentrations of products raised to divided by product of equilibrium concentrations of reactants raised to stoichiometric coefficients
- For general reaction: , equilibrium constant expression is:
- value is determined by reaction thermodynamics and independent of initial concentrations
- To calculate equilibrium concentrations:
- Write balanced chemical equation and equilibrium constant expression
- Determine initial concentrations of reactants and products
- Set up (Initial, Change, Equilibrium) to solve for equilibrium concentrations
- Define change in concentration using stoichiometric coefficients and a variable ()
- Add or subtract change from initial concentrations to obtain equilibrium concentrations in terms of
- Substitute equilibrium concentrations into equilibrium constant expression and solve for
- Calculate equilibrium concentrations using value (synthesis of ammonia)
- The can be used to determine the direction of a reaction by comparing it to the equilibrium constant
Reaction Kinetics and Equilibrium
- studies the rates of chemical reactions and factors affecting them
- can proceed in both forward and reverse directions
- occurs when the concentrations of reactants and products remain constant over time, which is characteristic of chemical equilibrium
- The equilibrium position refers to the relative amounts of reactants and products present at equilibrium
Key Terms to Review (29)
Catalyst: A catalyst is a substance that increases the rate of a chemical reaction without being consumed or altered itself. Catalysts play a crucial role in various chemical processes, including reaction mechanisms, catalysis, chemical equilibria, and shifting equilibria.
Catalysts: Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They work by lowering the activation energy needed for the reaction to proceed.
Chemical Kinetics: Chemical kinetics is the study of the rates of chemical reactions and the factors that influence those rates. It examines the speed at which reactants are converted into products, providing insights into the mechanisms and pathways of chemical processes.
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: Equilibrium in chemistry occurs when the rates of the forward and reverse reactions are equal, resulting in no net change in the concentration of reactants and products. This state can be reached in both closed systems and dynamic processes.
Equilibrium: Equilibrium is a state of balance or stability in a system, where the opposing forces or processes are in a state of dynamic balance. It is a fundamental concept that underpins various aspects of chemistry, including phase changes, chemical reactions, and thermodynamic processes.
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.
Heterogeneous equilibrium: Heterogeneous equilibrium involves reactants and products in different phases, such as solids, liquids, and gases. The equilibrium constant expression for these systems only includes the concentrations of the gaseous and aqueous species.
Heterogeneous Equilibrium: A heterogeneous equilibrium is a state of balance that exists between chemical species in a system where at least one of the reactants or products is in a different physical state, such as a solid, liquid, or gas, from the others. This type of equilibrium is an important concept in the context of chemical equilibria and equilibrium calculations.
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.
ICE Table: An ICE table, also known as an Initial, Change, and Equilibrium table, is a tool used in chemistry to organize and analyze the concentrations of reactants and products in a chemical equilibrium system. It provides a structured way to visualize and calculate the changes in concentrations as a reaction approaches equilibrium.
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.
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.
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.
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.
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.
Stoichiometric Coefficients: Stoichiometric coefficients are the numbers that appear in front of the chemical species in a balanced chemical equation, representing the relative quantities of reactants and products involved in the reaction. They are essential for understanding the quantitative relationships between the substances participating in a chemical equilibrium.
ΔG: ΔG, or Gibbs free energy change, is a thermodynamic quantity that represents the maximum amount of non-expansion work that can be extracted from a closed system under constant temperature and pressure conditions. It is a crucial concept in understanding chemical equilibria and the spontaneity of chemical reactions.
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.