Chemical Equilibrium

Dynamic Equilibrium

• Rate of forward reaction = Rate of reverse reaction

• Concentration of reactants and products are constant

• Closed system/ environment

Le Chateliers Principle

The position of the dynamic equilibrium shifts to minimise the effect of any change

3 factors affecting the position of equilibrium

• Concentration

• Pressure

• Temperature

Concentration: Increase concentration of reactants / Decrease concentration of products

• Position of the equilibrium will shift to the right

• To decrease the concentration of reactants/ increase the concentration of products

Concentration: Decrease concentration of reactants/ Increase concentration of products

• Position of the equilibrium will shift to the left

• To increase the concentration of reactants/ decrease the concentration of products

Pressure

• Increase: Position will shift to the side with fewer moles e.g. left/right

• Decrease: Position will shift to the side with more moles e.g. left/right

Temperature: Increase

• Forward reaction is endothermic/ exothermic

• Position of the equilibrium will shift in the endothermic direction e.g. left/right

Temperature: Decrease

• Forward reaction is endothermic/ exothermic

• Position of the equilibrium will shift in the exothermic direction e.g. left/right

Adding a catalyst effect on yield and position

• No effect on the yield or position of the equilibrium

• Will increase the rate of the forward and backward reaction equally

Equilibria and Industrial Processes: Rate

• Temperature: Low temperature will decrease the rate of reaction

• Pressure: High pressure will increase the rate of reaction

Equilibria and Industrial Processes: Issues

• Pressure: High pressure is expensive to generate and is a safety risk

• Temperature: High temperature increases energy costs

Equilibria and Industrial Processes: Optimum conditions

• Temperature: Increase temperature to balance yield and rate

• Pressure: Decrease pressure to balance yield, cost and maintain safety

Homogenous Equilibrium

A system in which the reactants and products are in the same phase

Heterogenous equilibrium

A system at equilibrium where not all substances are in the same phase

Kc Values

• If Kc<1 the position of the equilibrium shifts to the left as there are more reactants than products

• If Kc>1 the position shifts to the right as there are more products than reactants

state two ways that the use of catalysts is beneficial

• Reaction can be carried out at a lower temperature

• Less fossil fuels burnt