By Kevin Beck – Updated Aug 30, 2022
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Heat is a form of energy measured in joules (J), the SI unit equivalent to one newton-meter. In everyday contexts we often use calories (1 cal = 4.18 J) or BTUs, but for scientific calculations the joule is standard.
Heat flows naturally from warmer to cooler regions. Although we cannot see heat itself, we infer its presence from temperature changes. Temperature represents the average kinetic energy of molecules in a substance; adding heat increases this kinetic energy and thus raises the temperature.
Calorimetry is the experimental method of determining how much heat is required to change a substance’s temperature. By placing a known mass of a material in a sealed calorimeter, adding a precise amount of heat, and measuring the resulting temperature rise, we can calculate its specific heat capacity.
The calorie—used on food labels as a kilocalorie (kcal)—is defined as the heat needed to raise 1 g of water by 1 °C (or 1 K). A 12‑ounce soda, for example, contains roughly 150,000 calories (150 kcal).
The fundamental relationship between heat, mass, temperature change, and specific heat is expressed as:
Q = m·C·ΔT
Here, Q is the heat added (in joules), m is the mass (grams), ΔT is the temperature change (Kelvin or °C), and C is the specific heat capacity (J/g·K).
Heat capacity refers to the total heat required to raise an object’s temperature by 1 K, expressed in J/K. It depends on the mass of the object. Specific heat capacity, measured in J/g·K, is an intrinsic property that allows comparison between different materials regardless of mass.
For example, water’s high specific heat capacity (~4.18 J/g·K) means it can absorb large amounts of heat with only a modest temperature rise—an essential trait for living organisms and climate regulation.
To determine the specific heat capacity experimentally, divide the heat added by the product of mass and temperature change:
C = Q / (m·ΔT)
Copper’s specific heat capacity is 0.386 J/g·K. To raise 1 kg (1,000 g) of copper from 0 °C to 100 °C:
Q = m·C·ΔT = (1,000 g)·(0.386 J/g·K)·(100 K) = 38,600 J = 38.6 kJ.
Thus, the heat capacity of this 1‑kg block of copper is 386 J/K (since 38,600 J are needed for a 100 K rise).
Understanding heat capacity and specific heat is critical for designing thermal systems, selecting heat‑sink materials, and predicting temperature changes in engineering, chemistry, and environmental science.
