Enthalpy is defined as the sum of which of the following?

Enthalpy is a thermodynamic quantity that reflects the total heat content of a system. It is defined as the sum of the internal energy of the system plus the product of its pressure and volume. This definition can be expressed mathematically as:

[ H = U + PV ]

where ( H ) represents enthalpy, ( U ) is the internal energy, ( P ) is the pressure, and ( V ) is the volume of the system. This relationship highlights how enthalpy accounts not only for the internal energy stored in the molecules of a substance but also the energy related to the system's pressure and volume, which affects its ability to do work.

In contrast, the other options do not accurately reflect the definition of enthalpy. The second option mentions mass and temperature, which are not directly part of the enthalpy equation. The third option refers to kinetic and potential energy, which are components of the internal energy but do not encompass the pressure-volume work that is crucial in defining enthalpy. Lastly, the fourth option discusses temperature and density, neither of which is included in the enthalpy definition. Thus, the correct answer underscores the critical factors that contribute to the concept of enthalpy in