Topic 6: Chemical Changes

Question 1

How can the rate of a chemical reaction be found? [2]

Answer 1

1. Quantity of reactant used
2. Quantity of product formed

Question 2

What is the equation for mean rate of reaction (reactant)?

Answer 2

Quantity of reactant used/time taken

Question 3

What is the equation for mean rate of reaction (product)?

Answer 3

Quantity of product formed/time taken

Question 4

Define ‘rate of reaction’

Answer 4

How fast the reactants are changed into products

Question 5

What is an example of a slow reaction?

Answer 5

Rusting of iron

Question 6

What is an example of a moderate reaction?

Answer 6

Metal magnesium reacting with acid

Question 7

What is an example of a fast reaction?

Answer 7

Explosions/fireworks

Question 8

Explain how increasing temperature increases the rate of reaction [4]

Answer 8

1. When temperature is increased, the rate is faster
2. Particles are moving faster
3. Which means there are more frequent collisions
4. And more collisions that exceed the activation energy

Question 9

Explain how increasing concentration increases the rate of reaction [3]

Answer 9

1. When concentration is increased, the rate is faster
2. There are more particles in a given volume
3. This means more frequent collisions

Question 10

Explain how decreasing particle size increases the rate of reaction [3]

Answer 10

1. As particle size decreases, the rate is faster
2. The solid reactant has a lower SA to volume ration
3. This allows more frequent collisions

Question 11

Explain how the use of a catalyst increases the rate of reaction [4]

Answer 11

1. Use of a specific catalyst makes rate faster
2. Collisions do not change
3. But are more likely to be successful
4. This is because there is a lower activation energy by following an alternative pathway

Question 12

What does it mean if a reversible reaction is at ‘equlibrium’?

Answer 12

The forward reaction is going at excatly the same rate as the backward reaction

Question 13

What happens at ‘dynamic equilibrium’?

Answer 13

Both reactions are still happening but there is no overall effect

Question 14

At equilibrium, are the amounts of reactants and products being formed the same?

Answer 14

No, they are just being formed at the same rate

Question 15

What does it mean if equilibrium lies to the right?

Answer 15

The concentration of products is greater than reactants

Question 16

What does it mean if equilibrium lies to the left?

Answer 16

The concentration of reactants is greater than products

Question 17

In a reversbile reaction, if the reaction is endothermic in one direction, what does the other direction have to be?

Answer 17

Exothermic

Question 18

What does ‘Le Chatelier’s Principle’ state?

Answer 18

If you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change

Question 19

What happens if you increase the concentration of reactants (of a system at equilibrium)?

Answer 19

The system will try to decrease it by making more products

Question 20

What happens if you decrease the concentration of products (of a system at equilibrium)?

Answer 20

The system will try to increase it by reducing the amount of reactants

Question 21

If you decrease the temperature, which way will the reaction move?

Answer 21

Exothermic (to produce more heat)

Question 22

If you increase the temperature, which way will the reaction move?

Answer 22

Endothermic (to decrease heat)

Question 23

What will happen if you increase the pressure?

Answer 23

System will move in direction where there are fewer particles

Question 24

What will happen if you decrease the pressure?

Answer 24

System will move in direction where there are more particles