👉 Isenthalpic, also known as an isothermal pressure, refers to the relationship between the internal energy of a substance and its temperature. It describes how much heat is required to raise or lower the temperature of a given amount of matter without changing its volume. The concept was first introduced by Joseph Louis Gay-Lussac in 1865. In thermodynamics, an isenthalpic system is one where the change in internal energy (ΔU) and the change in entropy (ΔS