AQA Chemistry GCSE Topic 6: The Rate and Extent of Chemical Changes

Vocabulary flashcards covering key definitions and principles from Topic 6 of the AQA Chemistry GCSE, including kinetics and equilibrium concepts.

Activation energy

The minimum amount of energy that particles must collide with to react.

Catalyst

A substance that increases the rate of reaction by providing a different pathway for the reaction that has a lower activation energy, without being used up during the reaction.

Collision theory

A theory stating that chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.

Effect of changing concentration on equilibrium

If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again; if the concentration of a product is decreased, more reactants will react until equilibrium is reached again.

Effect of changing pressure on equilibrium

An increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules, while a decrease in pressure causes it to shift towards the side with the larger number of molecules.

Effect of changing temperature on equilibrium

If the temperature of an equilibrium system is increased, the relative amount of products at equilibrium increases for an endothermic reaction and decreases for an exothermic reaction.

Effect of concentration on reaction rate

Increasing the concentration of reactants in solution puts the reacting particles closer together, leading to more frequent collisions and a higher rate of successful collisions.

Effect of pressure on reaction rate

Increasing the pressure of gaseous reactants means the reacting particles are closer together, resulting in more frequent collisions and a higher rate of successful collisions.

Effect of surface area on reaction rate

Increasing surface area means there are more exposed reacting particles, which leads to more frequent successful collisions and a faster rate of reaction.

Effect of temperature on reaction rate

Increasing temperature gives particles more kinetic energy so they move faster and collide more often; additionally, a larger proportion of particles will have at least the activation energy.

Equilibrium

A state reached when a reversible reaction occurs in an apparatus that prevents the escape of reactants and products, and the forward and reverse reactions occur at exactly the same rate.

Le Chatelier’s Principle

The principle that if a reaction at equilibrium is subjected to a change in concentration, temperature, or pressure, the position of equilibrium will move to counteract the change.

Rate of reaction

The measure of the amount of product formed or reactant used over time, which may be given in units of $g/s$, $cm^3/s$, or $mol/s$.

Reversible reaction

A reaction in which the products can react together to form the original reactants, the direction of which can be changed by changing the conditions.