if a chemical system at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will shift to counteract the change.

It allows you to predict the affect of any changes made to a system at equilibrium.

The position of equilibrium will shift in the exothermic direction, to produce more heat (and counteract the decrease in temperature).

The position of equilibrium will shift in the endothermic direction in order to decrease the temperature (and counteract the increase in temperature).

The equilibrium will shift to the side with fewer molecules (moles) of gas, to reduce the pressure (and counteract the increase in pressure).

The equilibrium will shift to the side with more molecules (moles) of gas, to increase the pressure (and counteract the decrease in pressure).

The equilibrium will shift to the right (products side), to reduce the reactant concentrations and restore equilibrium.

The equilibrium will shift to the left (reactants side), to increase the reactant concentrations and restore equilibrium.

A catalyst will have no effect on the position of equilibrium.

A catalyst increases the rate of both forward and reverse reactions by the same amount so the position of equilibrium remains unchanged.

A catalyst does, however, increase the rate at which an equilibrium is established.

1The position of equilibrum.

2The rate of reaction.

3The costs of building and running the plant.

1. Higher pressures shift the equilibrium position to the right, but compressing the gases to high pressures is expensive. A compromise of 200 atm is chosen.
2. Higher temperatures increase the rate of reaction but shift the equilibrium position to the left. Plus, higher temperatures mean higher energy costs. A compromise of 450 °C is chosen.
3. An iron catalyst is used to speed up the rate of reaction.

1. Higher pressures shift the equilibrium position to the right, but compressing the gases to high pressures is expensive and dangerous (SO₃ is a highly acidic gas). A compromise of 2 atm is chosen.
2. Higher temperatures increase the rate of reaction but shift the equilibrium position to the left. Plus, higher temperatures mean high energy costs. A compromise of 450 °C is chosen.
3. A vanadium(V) oxide catalyst is used to speed up the rate of reaction.

If the temperature is increased, the position of equilibium moves in the endothermic direction.

If the temperature is decreased, the position of equilibium moves in the exothermic direction.

Catalysts increase the rate at which equilibrium is attained.

1. Concentration of reactants and products.
2. Pressure (only affects gases).
3. Temperature.