AQA GCSE Combined Science Chemistry -The Rate and Extent of Chemical Change

paper 2

What is the rate of a chemical reaction?

How quickly reactants are turned into products.

What is the formula for rate of reaction?

Rate = amount of reactant used or product formed ÷ time

What units are used for rate of reaction?

g/s, cm³/s, or mol/s depending on what's measured.

What are the main factors that affect rate?

Temperature, concentration, pressure, surface area, catalysts.

How does increasing temperature affect rate?

Particles move faster → more frequent and energetic collisions.

How does increasing concentration or pressure affect rate?

More particles in the same space → more frequent collisions.

How does increasing surface area affect rate?

More exposed particles → more frequent collisions.

What does a catalyst do?

Speeds up a reaction by lowering activation energy without being used up.

What is collision theory?

Particles must collide with enough energy to react.

What is activation energy?

The minimum energy needed for a reaction to happen.

How can you measure rate with a gas?

Collect gas in a syringe or measuring cylinder over time.

How can you measure rate using a change in mass?

Place reaction on a balance and measure loss of mass as gas escapes.

What is a reversible reaction?

A reaction where products can react to form the original reactants.

What does ⇌ mean?

It shows a reaction is reversible.

What happens at equilibrium?

The forward and backward reactions occur at the same rate.

What is Le Chatelier’s Principle?

If conditions change, the equilibrium shifts to counteract the change.

How does increasing temperature affect equilibrium?

Shifts in the direction of the endothermic reaction.

How does decreasing temperature affect equilibrium?

Shifts in the direction of the exothermic reaction.

How does increasing pressure affect equilibrium (gases only)?

Shifts to the side with fewer gas molecules.

How does decreasing pressure affect equilibrium (gases only)?

Shifts to the side with more gas molecules.

How does increasing concentration affect equilibrium?

Shifts away from the increased substance.

How does decreasing concentration affect equilibrium?

Shifts toward the decreased substance.

Is equilibrium affected by a catalyst?

No – it just helps the system reach equilibrium faster.

Why are reversible reactions important in industry?

They help maximise yield and reduce waste.

What is dynamic equilibrium?

When both reactions occur at the same rate and concentrations remain constant.