The Rate and Extent of Chemical Change

Question 1

How do you calculate mean rate of reaction?

Answer 1

Mean = Quantity of reactant used / time taken
OR
Mean = Quantity of product formed / time taken

Question 2

What are the factors that affect the rate of chemical reactions?

Answer 2

Concentration
Presence of catalysts
Surface area of solid reactants
Pressure of gases
Temperature

Question 3

What is temperature?

Answer 3

A measure if the average kinetic energy of its particles.

Question 4

What is the pressure of a gas?

Answer 4

A measure of how much force it exerts on its container and on objects inside it.

Question 5

What is a catalyst?

Answer 5

A substance that increases the rate of reaction but by the end of the reaction is unchanged chemically or in mass.

Question 6

What needs to happen for a chemical reaction to occur?

Answer 6

Reactant particles need to collide with each other and the colliding particles need to have enough energy.

Question 7

What is activation energy?

Answer 7

The minimum amount of energy that particles need for a reaction to happen.

Question 8

Why is the rate of reaction greater if the reactant is powder than if it is a lump?

Answer 8

As the particle size decreases, the surface area to volume ratio increases. More of the reactant is exposed to particles of the other reactant. The energy of the particles doesn’t change the frequency of successful collisions increases.

Question 9

How can you tell if a substance in a reaction mixture acts as a catalyst?

Answer 9

It is not shown in the chemical equation for the reaction by increases the rate of reaction.

Question 10

Give an example of an enzyme used in chemistry.

Answer 10

Fermentation to make ethanol using enzymes in yeast.

Question 11

If a reaction is endothermic in one direction, what is it in the other direction?

Answer 11

Exithermic

Question 12

What does an increase in temperature cause?

Answer 12

An increase in the frequency of collisions and an increase in the energy of the particles.
A shift in the equilibrium position in the direction of the endothermic change.

Question 13

What happens if you increase the pressure of a reacting gas in an equation?

Answer 13

The equilibrium position moves towards the side that has the smallest amount of gas molecules.

Question 14

What effect on equilibrium position does an increase in concentration cause?

Answer 14

A shift away from the substance that is increased in concentration.

Question 15

What effect does adding catalyst have on equilibrium position?

Answer 15

No change.

Question 16

Explain why doubling the concentration doubles the rate of reaction.

Answer 16

Doubling the concentration doubles the number of particles in the same volume. This doubles the frequency of successful collisions.

Question 17

What effect does increasing the temperature have in terms of collision theory?

Answer 17

It gives particles more energy so they are more likely to collide with enough energy to react.

Question 18

How can you tell on a graph when equilibrium has been reached?

Answer 18

Both lines are horizontal.

Question 19

What is Le Chatelier’s principle?

Answer 19

When a change in conditions is imposed on a system at equilibrium, the system responds in a way that counteracts this change.

Question 20

How does a catalyst affect the rate of reaction?

Answer 20

It provides an alternative pathway which has a lower activation energy.

Question 21

How is equilibrium reached?

Answer 21

When in a closed system the forward and reverse reactions happen at the same rate.