Wärmemenge

Wärmemenge, in thermodynamics, is the amount of heat transferred between a system and its surroundings during a process. It is denoted by Q and measured in joules in the SI system. Unlike internal energy or entropy, Wärmemenge is a path function; its value depends on the specific path taken from the initial to the final state, not solely on those states.

In thermodynamic sign convention, heat added to the system is positive, heat released is negative. The Wärmemenge is related to other quantities by the first law of thermodynamics: ΔU = Q − W, where ΔU is the change in internal energy and W is work done by the system.

Calculating Wärmemenge for common cases: If a homogeneous substance with mass m and specific heat capacity c (which may depend on temperature) is heated from T1 to T2 with no phase change, the heat added is Q = ∫ m c(T) dT. If c is constant, Q = m c ΔT. During a phase change at a fixed temperature, the Wärmemenge includes latent heat: Q = m L, where L is the latent heat of fusion or vaporization.

For a reversible path, the Wärmemenge connects to entropy via Q_rev = ∫ T dS. In irreversible processes, Q is less directly tied to state changes and must be determined from the path or using the first law with appropriate work terms.

Wärmemenge is related but distinct from heat capacity (Wärmekapazität), which measures how much heat is required to raise the temperature of a substance by one degree under specified conditions.