How to use it
- Choose what to find: heat, mass, specific heat capacity or final temperature.
- Pick the material, or Custom value to type c in J/(kg·K).
- Enter the mass and the start temperature, then the end temperature or the heat.
- Read the result, the temperature change and the heat in kJ.
Formula
Q = m × c × ΔT, ΔT = T end − T start
- m = Q ÷ (c × ΔT), c = Q ÷ (m × ΔT), ΔT = Q ÷ (m × c);
- 1 cal = 4.184 J, 1 kcal = 4184 J;
- a negative Q means heat is given off (cooling).
The material values are typical specific heats near room temperature (ice near 0 °C); reference tables differ by around 1%.
Worked example
Heating 1 kg of water from 20 °C to 100 °C: Q = 1 × 4186 × 80 = 334,880 J = 334.88 kJ, the energy to bring a litre of water to the boil, ignoring losses.
10 kJ put into 2 kg of aluminium at 20 °C: ΔT = 10,000 ÷ (2 × 897) = 5.57 °C, so it ends at 25.57 °C.
Tips
- Mind the sign. Cooling from 80 to 30 °C gives a negative heat: the water gives energy away.
- Use mass, not volume. For water 1 L is about 1 kg; for other liquids multiply by the density.
- Real heating takes longer. Kettles and pans lose heat to the air and warm themselves too.