For a pure substance in solid form, how does enthalpy change relate to internal energy change?

Question

Question

engineering Mechanical-Engineering

Answer 1

Answer #1

Enthalpy (H) is defined as the amount of energy content of a system (U+PV)

Entropy (S) defines the degree of randomness or disorder in a system.

Therefore, there is no direct relationship between entropy and enthalpy. However, the free energy (G) regroups both terms as:
G=H−TS

where at constant temperature, the change on free energy is defined as: ΔG=ΔH−TΔS.

Therefore, the free energy expression provides a relationship between enthalpy and entropy.

Thus, for a system at equilibrium, ΔG=0, and then we find that ΔS=ΔHT

Answer 2

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