Question

What Is The Significance Of Enthalpy In the Second Law Of Thermodynamics?

Answer 1

Enthalpy:

• Enthalpy is a state function.
• The enthalpy, H, is equal to the sum of the internal energy, U, and the product of the pressure, P, and volume, V, of the system.
• It can be expressed as: $\mathrm{H}=\mathrm{U}+\mathrm{pV}$.
• H is a state function because it depends on U, p, and V, all of which are state functions.
• Therefore, $∆\mathrm{H}$ is independent of the path.
• Thus, it can be expressed as: $∆\mathrm{H}=∆\mathrm{U}+\mathrm{p}∆\mathrm{V}$.

Significance of Enthalpy in the second law of thermodynamics:

• As per the second law of thermodynamics, the entropy change in an isolated system can only be positive or zero.
• Therefore, a process can be feasible only when the change in the entropy of the universe is positive.
• The change in enthalpy conveniently quantifies the heat flow of reactions.