Reactions that warm or cool their surroundings, where the energy goes, and everyday uses of both.
What you will learn
- Classify a reaction from a temperature change
- Give examples and uses of exothermic and endothermic reactions
- Link the energy change to bonds broken and made
Warmer or cooler
Energy is conserved in a reaction: it moves between the chemicals and their surroundings.
- Exothermic: energy is transferred to the surroundings, so the temperature of the surroundings rises. Combustion, respiration, neutralisation, most oxidation reactions. Uses: hand warmers, self-heating cans.
- Endothermic: energy is taken in from the surroundings, so the temperature falls. Thermal decomposition, photosynthesis, citric acid with sodium hydrogencarbonate. Uses: instant cold packs for sports injuries.
- Start 20.0 °C, end 27.5 °C
- change = 27.5 − 20.0 = +7.5 °C
- a rise, so exothermic
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Warmer or cooler
- Bonds are the reason
- Try it: Read the temperatures
9 practice questions, marked as you go; about 15 minutes in all.
Key terms
Takes in, Releases, Bond energy
In this unit: Energy changes
Exothermic and endothermic reactions, the temperature change practical, reaction profiles, bond energies, cells and fuel cells.
- Exothermic and endothermic reactions
- Required practical: temperature changes
- Reaction profiles
- Bond energies
- Chemical cells and fuel cells