c8: rates of reaction

What is the rate of reaction?

The change in the amount of reactant or product over time.

Give the formula for rate of reaction.

Rate = amount of reactant used or product formed ÷ time.

What are three ways to measure rate of reaction?

• Change in mass (if gas produced)

• Volume of gas produced (gas syringe)

• Change in colour or turbidity (e.g. disappearing cross).

What is collision theory?

Particles must collide with enough energy (activation energy) for a reaction to occur.

How does temperature affect the rate of reaction?

Higher temperature → particles move faster → more frequent and energetic collisions → faster rate.

How does concentration (or pressure) affect the rate?

More particles per volume → more frequent collisions → faster rate.

How does surface area affect rate?

Larger surface area → more particles exposed → more collisions → faster rate.

What does a catalyst do?

Increases rate by providing an alternative reaction pathway with lower activation energy.

What is activation energy?

The minimum energy needed for particles to react when they collide.

What does the gradient of a reaction rate graph show?

The rate of reaction — steeper gradient = faster reaction.

What happens to the line on a reaction graph when the reaction finishes?

It flattens (levels off) because all reactants are used up.

How can you calculate the mean rate of reaction?

Mean rate = change in quantity ÷ time taken.

How do you find the instantaneous rate at a given time on a graph?

Draw a tangent to the curve at that point and find its gradient.

Name five factors that affect the rate of reaction.

Temperature, concentration, pressure (for gases), surface area, and catalysts.