Equation
The equation is
where R is the gas constant. This can also be written as
The equation is approximate in that both enthalpy and entropy changes of a process (reaction) are assumed to be constant with temperature. A major use of the equation is to estimate a new equilibrium constant at a new absolute temperature. This can be seen by taking the definite integral of this differential equation between temperatures T1 and T2 giving
In this equation K1 is the equilibrium constant at absolute temperature T1 and K2 is the equilibrium constant at absolute temperature T2.
From the definition of Gibbs free energy
where S is the entropy of the system, and the reaction isotherm equation
it follows that
Therefore, a plot of the natural logarithm of the equilibrium constant versus the reciprocal temperature gives a straight line. The slope of the line is equal to minus the standard enthalpy change divided by the gas constant, -ΔHo/R and the intercept is equal to the standard entropy change divided by the gas constant, ΔSo/R. Differentiation of this expression yields the van 't Hoff equation.
Read more about this topic: Van 't Hoff Equation
Famous quotes containing the word equation:
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