Factors which affect the rates of chemical reactions Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Foundation

How does changing a reactant’s concentration affect the rate of a reaction in solution, and why?

Increasing concentration puts more reactant particles in a given volume, causing more frequent collisions and a faster reaction. Decreasing concentration has the opposite effects.

Why can a solid reactant react only at its surface?

Particles from the other reactant can reach it only at its surface.

Why does a powdered solid react faster than the same solid in large lumps?

The powder has more exposed surface area, allowing more collisions per second and increasing the reaction rate.

How does changing pressure affect the rate of a reaction involving gases, and why?

• Increasing pressure: particles are closer together in a smaller volume, so collisions are more frequent and the reaction is faster.
• Decreasing pressure: particles are farther apart, so collisions are less frequent and the reaction is slower.

How does changing temperature affect the rate of a chemical reaction?

Increasing temperature increases the reaction rate; lowering temperature decreases it.

How does changing temperature affect the kinetic energy and speed of reacting particles?

Increasing temperature gives particles more kinetic energy, so they move faster. Lowering it gives them less kinetic energy.

How does changing temperature affect the frequency of collisions between reacting particles?

Increasing temperature makes collisions more frequent; lowering it makes them less frequent.

Why does increasing temperature make successful collisions more likely?

Particles collide with more energy.

What is a catalyst?

A substance that increases a reaction’s rate without being used up by the reaction.

How does a catalyst make a reaction easier to occur?

It provides an alternative reaction pathway that requires less energy than the uncatalysed pathway.

How does a catalyst affect the number of successful collisions in a given time?

More successful collisions occur in that time, so the reaction is faster.