Heat and Calorimetry 14.1 Heat Heat is the energy transferred between systems which have different temperatures and are therefore not in thermal equilibrium. Heat only describes energy transferred, and hence, we do not speak of objects as containing heat. If heat flows from a table top into a cold glass of water sitting on it, the internal energy of the glass of water increases and the internal energy of the table top decreases by the same amount. However, the temperatures of the two systems does not in general change by the same amount. It is important not to equate temperature with internal energy.
Different materials have different relationships between internal energy and temperature.
For example, if I submerge an ice cube in water in a styrofoam cup and allow them to come to thermal equilibrium, the heat flowing out of the water must equal the heat flowing into the ice cube to the extent that no heat is gained or lost to the surrounding environment.