# Dynamic Equilibrium

Dynamic equilibrium
Features:
· Rate of forward reaction = Rate or reverse reaction
· Macro properties remain constant (constant temperature, pressure, concentration)
· Constant movement on the microscopic scale
· Closed system

Examples

N2 + 3H2 2NH3

CH3COOH + C2H5OH CH3COOC2H5 + H2O

CaCO3 CaO + CO2

#### Le Chatelier’s principal

When the conditions affecting the position of dynamic equilibrium change, the position of equilibrium shifts to minimise the change.

Effect of pressure on the position of equilibrium

N2(g) + 3H2(g) 2NH3(g)

An increase in pressure results in the position of equilibrium shifting to the right, due to the smaller number of moles (four on the left, two on the right) resulting in more NH3 being produced.

Effect of temperature on the position of equilibrium

CaCO3 CaO + CO2 H = +178 KJmol-1

If the temperature is increased the position of equilibrium will shift to the right because the forward reaction is exothermic so more CaO + CO2 will be formed.

Effect of catalyst
Catalysts have no effect on the position of equilibrium; it increases the rate of both the forward and reverse reactions.

Ways to increase the yield of product in a reaction. For example:

CaCO3 CaO + CO2 H = +178 KJmol-1

1. Remove the products as they are formed to increase the amount of reactions
2. Lower the pressure because there are more moles of reactants on the right
3. Increase the temperature because the forward reaction is endothermic

### The Haber process

Ammonia is an important product used in fertilisers in the form of ammonium sulphate (NH4)2SO4 and ammonium nitrate NH4NO3. It is also used in explosives (in particular TNT) and nylon.

N2(g) + 3H2(g) 2NH3(g) H = -92 KJmol-1

Conditions to produce maximum yield
1. Decrease the temperature because the forward reaction is exothermic
2. Increase the pressure because there are more moles of gas on the left

Problems: Low temperature decreases the rate of reaction
High pressure is expensive and dangerous

Compromise: 200 atm pressure increasing the rate of reaction, whilst keeping costs down
Remove ammonia as it forms and recycle the unreacted N2 and H2
Iron catalyst to speed up the rate of reaction
400°C temperature giving a quick rate of reaction, however it will decrease the yield