- In exothermic reactions energy is given out to the surroundings so the temperature of the surroundings increases.
- Combustion, oxidation and neutralisation reactions are typical exothermic reactions.
- Hand warmers used in the winter time are based on the release of heat from an exothermic reaction.
- Self-heating cans of food and drinks such as coffee and hot chocolate also use exothermic reactions in the bases of the containers.
Diagram showing the transfer of heat energy outwards from an exothermic reaction
- In endothermic reactions energy is taken in from the surroundings so the temperature of the surroundings decreases.
- These types of reactions are much less common than the exothermic reactions.
- Electrolysis, thermal decomposition reactions and the first stages of photosynthesis are typical endothermic reactions.
- Sports injury treatment often use cold packs based on endothermic reactions to take heat away from a recently injured area to prevent swelling.
Diagram showing the transfer of heat energy from the surroundings into an endothermic reaction
To perform a calorimetric study of the reaction between HCl and NaOH.
The temperature change will vary depending on the amounts of solutions involved.
- dilute hydrochloric acid
- dilute sodium hydroxide solution
- styrofoam calorimeter & lid
- 25cm3 measuring cylinder
- thermometer & stirrer
Diagram showing the apparatus for the calorimetry investigation for displacement, dissolving and neutralisation Practical Tip:
The lid should be placed on the calorimeter as soon as the acid is added to minimise heat loss to the surroundings.
- Using a measuring cylinder, place 25 cm3 of the NaOH into the calorimeter.
- Measure and record the temperature of the solution.
- Add 5cm3 of the dilute HCl and stir.
- Measure and record the highest temperature reached by the mixture.
- Repeat steps 1 – 4 increasing the amount of acid added by 5cm3 each time.
Record your results in a suitable table, eg:
Plot a graph of the results and draw a line of best fit, using the graph to determine what volume of acid causes the biggest change in temperature.
The larger the difference in the temperature the more energy is absorbed or released.