Catalysts & Reaction Profiles & Rate affected by: Temperature, Surface Area, Pressure, Concentration

What happens to reaction rate when concentration increases?

The rate of reaction increases.

Explain why increasing concentration increases rate.

There are more reacting particles in a given volume. -- Therefore particles collide more frequently. -- So there are more successful collisions per unit time. -- Therefore the rate of reaction increases.

What happens to the rate of a reaction between gases when pressure increases?

The rate increases.

Explain why increasing pressure increases reaction rate.

Gas particles are closer together / there are more particles per unit volume. -- Collisions occur more frequently. -- There are more successful collisions per unit time. -- Rate increases.

What happens when the surface area of a solid reactant increases?

The rate of reaction increases.

Explain why increasing surface area increases rate.

More reacting particles are exposed at the surface. -- Therefore collisions between reactant particles occur more frequently. -- There are more successful collisions per unit time. -- Rate increases.

How can you increase the surface area of a solid?

Break it into smaller pieces or use a powder.

Why do smaller pieces have a greater surface area-to-volume ratio?

Breaking the same volume into smaller pieces exposes more surface relative to the volume.

What happens when temperature increases?

The rate of reaction increases.

Explain why increasing temperature increases reaction rate.

Particles have more kinetic energy. -- They move faster. -- They collide more frequently. -- A greater proportion of collisions have energy equal to or greater than the activation energy. -- Therefore there are more successful collisions per unit time. -- Rate increases.

What is a catalyst?

A substance that increases the rate of a chemical reaction but is not used up during the reaction.

How does a catalyst increase reaction rate?

It provides a different reaction pathway with a lower activation energy.

Why does lowering activation energy increase rate?

A greater proportion of collisions have sufficient energy to react, so there are more successful collisions per unit time.

Is a catalyst included as a reactant in the chemical equation?

No, because it is not used up during the reaction.

Do all reactions use the same catalyst?

No. Different reactions require different catalysts.

What are biological catalysts called?

Enzymes.

What does the activation energy represent on a reaction profile?

The energy difference between the reactants and the top of the energy barrier.

How would a catalysed reaction profile differ?

It has a lower activation-energy peak/barrier.

Does a catalyst change the overall energy change of a reaction?

No. It changes the activation energy, not the overall energy difference between reactants and products.