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Transcript
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 - TSof Elements and Compounds: Cp increases slowly with temperature HoT - Ho298 = Cp dT Cp [T2 – T1] SoT not zero except at 0 K —