C5 - Energy Changes

Question 1

What happens in an exothermic reaction?

Answer 1

Energy is given out to the surroundings

Question 2

What happens to the temperature of surroundings in exothermic reactions?

Answer 2

Increases

Question 3

Types of exothermic reactions?

Answer 3

• Combustion
• Oxidation
• Neutralisation

Question 4

Two specific exothermic reactions?

Answer 4

• Hand warmers

- Self heating cans of food and drinks

Question 5

What happens in endothermic reactions?

Answer 5

Energy is taken in from the surroundings

Question 6

What happens to the temperature of the surroundings in an endothermic reaction?

Answer 6

Decreases

Question 7

Types of endothermic reactions?

Answer 7

• Electrolysis
• Thermal decomposition
• Photosynthesis

Question 8

Specific endothermic reaction?

Answer 8

Cold packs for sports injuries

Question 9

What is activation energy?

Answer 9

The minimum amount of energy required for a successful collision

Question 10

What is on the x axis on a reaction profile?

Answer 10

Energy

Question 11

What is on the y axis on a reaction profile?

Answer 11

Progress of reaction

Question 12

What is bond energy?

Answer 12

The amount of energy required to break the bond or the amount of energy given out when the bond is formed

Question 13

How do you calculate energy change?

Answer 13

Energy taken in - Energy given out

Question 14

What is a chemical cell?

Answer 14

A source of electrical energy

Question 15

Why are alkali batteries not rechargeable?

Answer 15

The reactions are irreversible so when one of the reactants are used up, the battery cannot be used

Question 16

How can rechargeable batteries be charged?

Answer 16

The reactions are reversed by connecting the cells to an external electrical supply

Question 17

How does a hydrogen cell work?

Answer 17

Hydrogen enters at the anode where it is oxidised and oxygen enters at the cathode where it is reduced

Question 18

Half equation that occurs at the cathode?

Answer 18

2H2 –> 4H+ + 4e-

Question 19

Half equation that occurs at the anode?

Answer 19

4H+ + O2 + 4e- –> 2H2O

Question 20

Overall reaction in a fuel cell?

Answer 20

2H2 + O2 –> 2H20

Question 21

Advantages of hydrogen fuel cell?

Answer 21

• Produce no pollution
• Produce more energy per kg than either petrol or diesel
• No batteries to dispose of which is better for environment
• Continuous process so will keep producing energy as long as fuel is supplied

Question 22

Disadvantages of hydrogen fuel cell?

Answer 22

• Materials used to produce fuel cells are expensive
• High pressure tanks needed for oxygen and hydrogen which is dangerous and difficult
• Affected at low temperature, becoming less efficient
• Hydrogen is expensive to produce and store