This question is about catalysts and equilibrium - AQA - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 2

A catalyst increases the rate of a reaction by providing a different reaction pathway that has a lower activation energy. This allows more reactant molecules to have sufficient energy to overcome the barrier, leading to a higher frequency of successful collisions.

Scientists can predict the effects of changing conditions on the position of an equilibrium in a closed system. This principle states that if an external change is applied to a system at equilibrium, the system adjusts to counteract that change.

A reversible chemical reaction reaches equilibrium when the rates of the forward and reverse reactions are equal. This is typically observed in a closed system which prevents the escape of reactants and products, allowing them to continually react with one another.

Increasing the pressure will increase the yield of ammonia because there are more moles of gas on the left-hand side of the reaction (N2 + 3H2) than on the right (2NH3). According to Le Chatelier's Principle, the system will shift to the side with fewer moles of gas to counteract the pressure increase.

Increasing the temperature will decrease the yield of ammonia because the forward reaction is exothermic. According to Le Chatelier's Principle, the system will shift in the endothermic direction to absorb the added heat, thus favoring the reactants over the products.