The energy change per mole of a substance is called what?

• A. Enthalpy
• B. Molar Enthalpy
• C. Internal Energy
• D. Temperature

Answer: (B)

Energy change per amount of substance points to a per-mole quantity of a thermodynamic property. Enthalpy is the heat content that matters for heat flow at constant pressure, and the change in enthalpy (ΔH) describes the energy change for a process. When you express that energy change on a per-mole basis, you get molar enthalpy. This is why the term that fits the description is molar enthalpy: it’s the enthalpy change divided by the number of moles, giving the energy change per mole.

Enthalpy alone describes the total energy content of a system and scales with how much material you have, not per mole. Internal energy is the energy stored within the system, which isn’t the same as the enthalpy change per mole, and temperature is a measure of average kinetic energy, not an energy change.