Beginner · 11 min
Heat and temperature
Distinguish temperature from heat transfer and calculate heating energy.
Temperature and energy transfer
Temperature describes how hot or cold something is. Heat is energy transferred because of a temperature difference, naturally from a hotter object to a colder one. A temperature reading does not tell us the total internal energy of an object. Mass and material matter too. Find a temperature change by subtracting the initial temperature from the final temperature.
Worked example
Water warms from 18 °C to 26 °C. Temperature change = 26 − 18 = 8 °C
Energy needed for heating
When there is no change of state, heating energy can be calculated with Q = m × c × ΔT. Here m is mass, c is specific heat capacity, and ΔT is temperature change. For liquid water, use c = 4,200 J/(kg·°C) in these exercises. This means raising 1 kg of water by 1 °C needs about 4,200 J. We ignore energy transferred to the container or surroundings.
Worked example
Heating 0.5 kg of water by 2 °C: Q = 0.5 × 4,200 × 2 = 4,200 J
Compare heating needs
- On paper, compare the energy needed to raise 1 kg and 2 kg of water by the same 3 °C. Use c = 4,200 J/(kg·°C).
- Explain why the larger mass needs more energy even though its temperature increase is the same.