Thermodynamic Symbols and Constants
Definition of Thermodynamic Symbols
E is the intrisic energy; (J/mol)
H is the enthalpy (= E + PV); (J/mol)
G is the Gibbs energy (= H – TS); (J/mol)
Cp is the heat capacity at constant temperature; (J/mol K)
The superscript o denotes the value given is for the standard reference state. For gases this is the
ideal gas state at 1 atm. For example Hv refers to the enthalpy of vaporization of the liquid phase
to the real gas at the saturation pressure, while Hov refers to the vaporization enthalpy of the pure
liquid to the ideal gas at 1 atm. For liquids and solids the standard state is the pure substance at 1
atm pressure.
HoT - Ho298 is the enthalpy at the standard state T less the enthalpy at the standard state at 298.15 K.
(GoT - Ho298)/T is the Gibbs energy function and is equal to (HoT - Ho298)/T - SoT. This function is
tabulated because it shows greater linearity than GoT thus facilitating interpolation between
temperatures.
SoT is the practical entropy in the standard state at temperature T omitting contributions from
isotopic mixing and nuclear spins.
 refers to the difference between the final state and the initial one. For example Hf is the
enthalpy of formation of substance A relative to the enthalpy of the elements of this substance
with each substance in a specified state. Hof is the enthalpy of formation of substance A relative
to the elements with each substance in its standard state at the specified temperature.
Kp is the equilibrium constant expressed in terms of pressure Kp = (Pa)m(Pb)n/(Pc)o(Pd)p.
GoT = -RT lnKp
Elements:
Compounds:
Hof = 0 at all temperatures
GoT = 0 at all temperatures
Hof = Hoproduct - Ho elements
Gof = Hof - TSof
Elements and Compounds:
Cp increases slowly with temperature
HoT - Ho298 = Cp dT  Cp [T2 – T1]
SoT not zero except at 0 K
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