C8- Rates of Reaction

Question 1

. How can you work out the rate of a chemical reaction? (2)

Answer 1

The rate of a chemical reaction can be found by measuring the quantity of a reactant used or the quantity of product formed over time: mean rate of reaction = quantity of reactant used / time taken mean rate of reaction = quantity of product formed / time taken

Question 2

2. How can the quantity of reactant or product be measure? (2)

Answer 2

The quantity of reactant or product can be measured by the mass in grams, by a volume in cm3.

Question 3

3. What are the units for rate of reaction? (2)

Answer 3

The units of rate of reaction may be given as g/s or cm3/s.

Question 4

4. When will a chemical reaction occur? (2 marks)

Answer 4

When reacting particles collide with each other AND with sufficient energy

Question 5

5. How can a graph of time vs amount of product produced be used to compare rates of reaction? (2 marks)

Answer 5

The steeper the gradient, the faster the reaction.

Question 6

6. What does it mean when the graph levels off and goes flat? (1 mark)

Answer 6

It means the reaction is complete and no more product is being produced

Question 7

7. Why do the lines curve before levelling off/going flat? (2 marks)

Answer 7

As the reaction proceeds the concentration of reactants decreases, decreasing the rate of reaction, so the gradient decreases. As the reaction proceeds, the concentration of product increases, which further decreases the concentration of reactants, decreasing the rate of reaction, so the gradient decreases.

Question 8

1. Name 2 factors which affect the rates of chemical reactions? (2)

Answer 8

Factors which affect the rates of chemical reactions include the surface area of solid reactants.

Question 9

2. How does changing the surface area of chemical reactants affect the rate of chemical reactions? (1)

Answer 9

Increasing the surface area leads to an increase in the rate of chemical reactions.

Question 10

3. Describe collision theory. (3)

Answer 10

Collision theory explains how various factors affect rates of reactions. According to this theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy. The minimum amount of energy that particles must have to react is called the activation energy.

Question 11

4. How does increasing the surface area of solid reactants affect the frequency of collisions?

Answer 11

Increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.

Question 12

1. What is the name of the minimum amount of energy that particles need to react? (1 mark)

Answer 12

Activation energy

Question 13

2. How does increasing the surface area of solid reactants affect the rate of reaction? (2 marks)

Answer 13

Increasing the surface area increases the frequency of collision and increases the rate of reaction.

Question 14

3. How does increasing the temperature affect the rate of reaction? (2 marks)

Answer 14

Increasing the temperature increases the speed of the reacting particles. This makes them collide more frequently and the rate of reaction increases.

Question 15

1. How does increasing the pressure of reacting gasses affect the rate of reaction? (2 marks)

Answer 15

Increasing the pressure increases the frequency of collisions and increases the rate of reaction.

Question 16

2. How does increasing the concentration of reactants affect the rate of reaction? (2 marks)

Answer 16

Increasing the concentration increases the frequency of collisions and increases the rate of reaction.

Question 17

3. How does increasing the surface area of solid reactants affect the rate of reaction? (2 marks)

Answer 17

Increasing the surface area increases the frequency of collision and increases the rate of reaction.

Question 18

4. What is a catalyst? (2 marks)

Answer 18

Catalysts change the rate of chemical reactions but do not get used up during the reaction.

Question 19

5. In what situations can catalysts be useful? (2 marks)

Answer 19

Catalysts are often used in industrial processes to reduce costs. They do this by a) speeding up the reaction so the product is produced more quickly b) allowing the reaction to be carried out at a lower temperature

Question 20

1. What happens with energy when a chemical reaction occurs? (2 marks)

Answer 20

Energy is either transferred to or from the surroundings

Question 21

2. What is a reversible reaction?

Answer 21

In a reversible reaction, the products can react to produce the original reactants again

Question 22

3. What is an exothermic reaction? (1 mark)

Answer 22

A reaction that gives out energy to the surroundings (these reactions can feel hot)

Question 23

4. Give some examples of exothermic reactions (3)

Answer 23

Combustion Many oxidation reactions Neutralisation

Question 24

5. What are some everyday uses of exothermic reactions?(2)

Answer 24

Self-heating cans (e.g for coffee). Hand warmers.

Question 25

6. What is an endothermic reaction?(1)

Answer 25

A reaction that takes in energy from the surroundings (these reactions can feel cold)

Question 26

7. Give some examples of endothermic reactions(1)

Answer 26

Thermal decomposition

Question 27

8. What are everyday uses of endothermic reactions?(1)

Answer 27

Sports injury packs

Question 28

9. If a reaction is reversible and is exothermic in one direction, what will it be in the opposite direction? (1 mark)

Answer 28

Endothermic

Exothermic

hydrated copper sulfate (blue) –><– anhydrous copper sulfate (white) + Water

Endothermic

Question 29

10. If a reaction is reversible and is endothermic in one direction, what will it be in the opposite direction? (1 mark)

Answer 29

Exothermic

Exothermic

hydrated copper sulfate (blue) –><– anhydrous copper sulfate (white) + Water

Endothermic

Question 30

11. What can be said about the energy given out and the energy taken in a reversible reaction? (1 mark)

Answer 30

They are the same (If a reaction gives out 100J in one direction then it will take in 100J in the other)

Question 31

1. Define a dynamic equilibrium (1)

Answer 31

A state of balance between continuing processes.

Question 32

2. Describe a closed system (1)

Answer 32

A system in which there is an exchange of energy (as heat or work) but not matter, with its surroundings.