Chemical equilibria

Dynamic equilibrium

Rates of forward and reverse reactions are the same

Net concentrations of the components of the reaction mixture remain constant

When is equilibrium reached?

When rates are equal

Le Chatelier’s principle

If any factor is changed which affects equilibrium, the position of equilibrium will shift so as to oppose or counteract the change

How does temperature affect equilibrium?

If temperature increases, equilibrium will shift to the endothermic direction as this takes in heat causing the temperature to decrease

If temperature decreases, equilibrium will shift to the exothermic direction as this will give out heat causing temperature to increase

How does concentration affect equilibrium?

If concentration of a substance is increased, equilibrium will shift to the other direction to decrease the amount substance

If concentration of a substance decreases, equilibrium will shift to increase the amount of the substance

How does pressure affect equilibrium?

If the pressure is increased the equilibrium shifts to decrease the pressure by shifting the direction of the fewest gas molecules

If the pressure is decreased the equilibrium shifts to increase the pressure by shifting to the direction of the most gas molecules

How does a catalyst affect equilibrium?

No change on the position of equilibrium

Increases rate of forwards and backwards reaction equally

Equilibrium is reached faster

What do compromised conditions take into accout?

Yield

Rate

Equipment cost

Energy cost

Ideal conditions for the Harber process

Low temperature

High pressure

Compromised conditions for Harber process

450 degrees → compromise between rate and yield

200 atm → compromise between yield and costs

What is Kc?

At equilibrium the ratio of the concentrations and reactants is constant

What does it mean if Kc is greater than 1?

Concentration of the products is greater than the concentration of reactants so equilibrium lies to the right hand side

What happens to Kc if coefficients are doubled?

Becomes Kc²

What happens to Kc if coefficients are halved?

Becomes root Kc

What happens to Kc if the reaction is reversed?

Becomes 1/ Kc

What is the only condition effecting Kc?

Temperature

How does temperature effect Kc?

Temperature can cause the position of equilibrium to change causing concentration of reactants and products to change