Factors that affect equlibrium

- explain the effect of changes of concentration and pressure on chemical systems at equilibrium by applying collision theory to the forward and reverse reactions - explain and predict the effect of temperature change on chemical systems at equilibrium by considering the enthalpy change for the forward and reverse reactions - apply Le Châtelier’s principle to predict the effect changes of temperature, concentration of chemicals, pressure and the addition of a catalyst have on the position of equilibrium and on the value of the equilibrium constant

Increased temperature

Greater proportion of particles have sufficient energy to overcome the activation energy

• and since the $E_a$(endothermic reaction) = $E_a$(exothermic reaction) + $|ΔH|$) the position of equilibrium will shift to favour the endothermic reaction.

Decreased temperature

lower proportion of particles have sufficient energy to overcome activation energy

• therefore the position of equilibrium will shift to favour the exothermic reaction

increased pressure/concentration

causes higher collision frequency → thus increasing the amount of successful collisions between particles

• in an equilibrium system this increases the rate of the reaction which has more mols of reactants

  • favouring the reaction (direction) which produces the least mols

decreased pressure/concentration

causes a lower collision frequency, thus decreasing the amount of successful collisions between particles

• in an equilibrium system this decreases the rate of the reaction which has more mols of reactant

  • favouring the reaction (direction) which produces the most mols

Le Châtelier’s principle

states that if a stress is applied to a system in equilibrium, the system will shift (partially adjust) in order to minimise the effect of the stress

Le Châtelier’s principle: changes of temp, concentration, pressure and the addition of a catalyst