IB Chemistry - Equilibrium (7)

Arrhenius equation

Arrhenius equation

k = Ae^(-Ea/RT)

Arrhenius equation rearranged

lnk = -Ea/R * 1/T + lnA

Catalyst effect on equilibrium

no effect

Le Chatelier's Principle

when stress is applied to a system at equilibrium, the system changes to relieve the stress

HEAT reaction mixture

Position of equilibrium shifts in the endothermic direction (to take up the heat)

COOL reaction mixture

Position of equilibrium shifts in the exothermic direction

Increase pressure of mixture

Equilibrium moves towards the direction with fewer gas molecules

Effect of concentration on equilibrium

Adding product: equilibrium shifts towards the reactantsAdding reactant: equilibrium shifts towards the products

equilibrium constant expression

[products]/[reactants]

What is the use of the equilibrium constant?

An equilibrium constant provides information about how far a reaction proceeds at a particular temperature

The reaction quotient (Q)

The ratio for the concentrations of the reactants and products (raised to the appropriate powers) at any point in time.

If Q<Kc

reaction proceeds to the right in favour of products

If Q>Kc

reaction proceeds to the left in favour of reactants

What affects the equilibrium constant?

temperature only

Increasing temperature on an exothermic reaction

the value of equilibrium constant decreases

Increasing temperature on an endothermic reaction

the value of equilibrium constant increases

Low Gibbs free energy

High entropy

The relationship between equilibrium and Gibbs free energy

The position of the equilibrium corresponds to the mixture of reactants and products that produces the minimum value of Gibbs free energy and the maximum value of entropy

Equilibrium constant (Gibbs free energy)

∆G = -RT*lnk

The relationship between partial pressure and concentration can be worked out using

PV = nRT = P = n/V*RT

partial pressure of a gas

[concentration]*RT

Equilibrium constant of gas

Kp = Kc * (RT)^ ∆n, where ∆n is the number of molecules of a gas on the right side of the equation minus the number of molecules of gas on the left side

Explaining the effect of changes in concentration on the position of equilibrium

The value of the equilibrium constant is not affected by a change in concentration

state of equilibrium

Q = Kc