Page 79 - Science Coursebook

5.4 Exothermic or endothermic?

This is an expensive idea because

of the difficulty of making the soup
compartments in the tin, so that the calcium oxide
compartments in the tin, so that the
food or drink is not contaminated. calcium and water
oxide heat
water
thin metal sheet
broken by pin
pressure
A self-heating can of soup.

Using endothermic reactions and processes
People sometimes use ice packs when they injure
themselves. These packs are stored in a fridge or freezer
until they are needed. When the ice pack is placed on
the injured area, the melting ice takes in heat from the
injured area. This is an endothermic process. It means
that the injured area is cooled and this often prevents it
from swelling up. After use, the ice pack can be placed
back in the freezer and used again.
Some ‘ice’ packs are made using substances that undergo
an endothermic process when they mix together.
These packs can be used even when you don’t have a
refrigerator or freezer. The pack has two compartments

inside, each containing a different substance. These
substances are usually ammonium nitrate and water.
When you push on the pack and break the compartment
containing ammonium nitrate, the water mixes with it A chemical ice pack being used to treat
and the ammonium nitrate begins to dissolve. This is an an injury.
endothermic process, so the temperature drops.

Questions
1 Explain why self-heating cans are very expensive.
2 Explain why a self-heating can can only be used once.

A+I 3 Describe one advantage and one disadvantage of each of the two types of
ice pack described above.

Summary

• Exothermic and endothermic reactions can be identified by taking
the temperature at the start and the end of the reaction.
• Exothermic and endothermic reactions and processes can be used to
produce useful items.

5 Energy changes 77