Defining Enthalpy Using Thermodynamics

The question asks for the thermodynamic property defined as the sum of a system's internal energy plus the product of its pressure and volume.

This quantity represents the total heat content of a system at constant pressure. It includes the internal energy ($U$) required to create the system and the energy ($PV$) required to make room for it by displacing its environment.

Enthalpy Formula

Mathematically, enthalpy ($H$) is defined by the equation:

$ H = U + PV $

• $H$ represents Enthalpy
• $U$ represents Internal Energy
• $P$ represents Pressure
• $V$ represents Volume

Correct Term Identification

Based on the definition and formula:

• Enthalpy is precisely the sum of internal energy ($U$) and the product of pressure ($P$) and volume ($PV$). This matches the question directly.

Why Other Options Are Incorrect

• Gibbs free energy ($G = H - TS$) relates enthalpy, entropy, and temperature, defining the maximum reversible work at constant temperature and pressure.
• Entropy ($S$) is a measure of the disorder or randomness in a system.
• Helmholtz free energy ($A = U - TS$) relates internal energy, entropy, and temperature, defining the maximum work obtainable from a closed system at constant temperature and volume.

Therefore, the correct term is Enthalpy.