specific heat

Water famously holds heat — coastal towns have milder weather because the sea warms and cools slowly. Specific heat is heat capacity with the how-much stripped out: the energy needed to raise one kilogram (or one mole) of a material by one degree. It tells you which material, kilo for kilo, is the better heat sponge.

Specific heat c is heat capacity divided by mass, c = C/m, with units of J/kg-K (mass basis) or J/mol-K (molar basis). Water's value is huge, about 4186 J/kg-K; aluminum is about 900, copper about 385, and lead about 130. So it takes roughly 11 times more energy to warm a kilogram of water than a kilogram of copper by the same amount. On a molar basis the picture becomes strikingly simple: most solid elements sit near 25 J/mol-K at room temperature (the Dulong-Petit value), because a mole always contains the same number of atoms and each vibrating atom stores about the same energy. The working formula is Q = m x c x dT.

Specific heat guides the choice of coolants and heat-storage materials (water is a superb coolant partly because of its high specific heat), sets the thermal mass of buildings, and is measured directly by DSC (differential scanning calorimetry) to locate melting points and glass transitions. Honest caveat: specific heat is not truly constant — it rises with temperature and spikes sharply near a phase change, so the flat catalog value is a room-temperature approximation.