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 ([ΔG](https://www.fiveableKeyTerm:ΔG)) of the system minimizes
(K) relates to standard Gibbs free energy change ([ΔG°](https://www.fiveableKeyTerm:ΔG°)) by equation: ΔG°=−RTlnK
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 (K) 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: aA+bB⇌cC+dD, equilibrium constant expression is: K=[A]a[B]b[C]c[D]d
K 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 (x)
Add or subtract change from initial concentrations to obtain equilibrium concentrations in terms of x
Substitute equilibrium concentrations into equilibrium constant expression and solve for x
Calculate equilibrium concentrations using x 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