4.9 Using Energy Transfers From Reactions

Question 1

In the hand warmers that can only be used once, what are 2 common reactions used for them?

Answer 1

• oxidisation of iron
• calcium oxide with water

Reactants are used up so can only be used once

Question 2

In the hand warmers that can be used multiple times, what are common reactions used for them?

Answer 2

•crystallisation of a salt

Question 3

How can we get the heat packs to re dissolve the salt?

Answer 3

Heat it in boiling water, can be used many times

Question 4

Suggest one advantage and one disadvantage of using reusable hand warmers instead of single use hand warmers

Answer 4

Pro: less resources wasted
Con: needs energy to be heated again

Question 5

Name a practical use of endothermic reactions?

Answer 5

Cold packs

Question 6

How do cold packs work?

Answer 6

Ammonium nitrate and water are kept separately. When mixed together the endothermic reaction takes place, taking in energy from the surroundings and becoming very cold. The reaction can’t be undone so can only be used once

Question 7

Name 2 ways ice packs can be used

Answer 7

• on sports injuries

* to cool drinks

Question 8

Suggest one advantage and one disadvantage of using chemical cold packs instead of an ice pack

Answer 8

Pro: can be used anywhere
Con: only be used once so wastes resources

Question 9

Name a practical use of exothermic reactions?

Answer 9

Hand warmers