Shomate equation

The Shomate equation allows for the calculation of enthalpy and entropy of various gas phase species. The main advantage of using these expressions is that the resulting energetic values are based on experiment rather than on theoretical considerations assuming ideal gases.

The Shomate equation for the enthalpy is given by

\[ H^{0}_{T} - H^{0}_{T=298.15} = A \cdot T + B \cdot \frac{T^{2}}{2} + C \cdot \frac{T^{3}}{3} + D \cdot \frac{T^{4}}{4} - \frac{E}{T} + F - H \]

while the corresponding equation for the entropy is given by

\[ S^{0}_{T} = A \ln(T) + B \cdot T + C \cdot \frac{T^{2}}{2} + D \cdot \frac{T^{3}}{3} - \frac{E}{2T^{2}} + G \]

The values for the parameters A-H can be found from thermodynamic tables. An example for gaseous water is provided here

Important

When using the Shomate equation, carefully verify that you are using the correct aggregation state (solid, fluid, gaseous). A common mistake is to mix the fluid and gaseous state.