Page 78 - Science Coursebook

5.4 Exothermic or endothermic?

In exothermic reactions and processes, heat energy is given out. In endothermic
reactions and processes, heat energy is taken in.

boiling water ice melting
cooling

heat given out heat taken in

Exothermic processes give out heat. Endothermic processes take in heat.

Activity 5.4

Exothermic or endothermic

SE Carry out each of the reactions or processes provided for you.
1 Place one of the solutions in the polystyrene cup.
2 Measure and record the temperature.
3 Add the other substance. thermometer
4 Allow the substances to react and then measure and record
the temperature.

Questions
A1 Why is a polystyrene cup used rather than a glass beaker? polystyrene cup
A2 Which reaction gave out the most heat energy? containing liquid
A3 Which reaction took in the most heat energy?

Using exothermic reactions
Some exothermic reactions are used to produce self-heating cans of
food or drink. For example, a can of self-heating coffee or self-heating

food contains two chemicals, which are in separate compartments.
When you press a button, the two chemicals mix with each other and
react. The reaction warms up the food or drink.
The chemicals used are calcium oxide and water. When the water and
calcium oxide are mixed together they react, and heat is given off.

calcium oxide + water → calcium hydroxide

76 5 Energy changes

A+E