By John Brennan, Updated Mar 24, 2022
In the early 19th century, British brewer and physicist James Joule demonstrated that heat and mechanical work are two expressions of the same energy. His insight earned him a lasting place in science; today, the unit for measuring energy and heat is named after him.
You can easily calculate the amount of heat absorbed or released by an object if you know its mass, the temperature change, and the material’s specific heat capacity.
Image credit: RazoomGames/iStock/GettyImages
Heat (in joules) = mass × ΔT × specific heat capacity.
Look up the specific heat capacity of your material. Common tables list values in kJ / kg K (kJ = kilojoules, kg = kilograms, K = Kelvin). One degree Kelvin equals one degree Celsius.
Subtract the initial temperature from the final temperature. If the change is given in Fahrenheit, convert it to Celsius with (°F – 32) × 5⁄9 = °C and then add 273.15 to obtain Kelvin.
Multiply the temperature change by the specific heat capacity and the mass to obtain the heat exchanged in joules.
Example: 10 kg of water heated from 10 °C to 50 °C.
Specific heat of water ≈ 4.184 kJ / kg K.
Heat = 10 kg × 40 °C × 4.184 kJ / kg K = 1673.6 kJ (≈ 1.67 MJ).
