Temperature and Pressure Dependence of the Equilibrium Constant

Let us first examine the temperature dependence of Keq (at constant P), taking as the starting point a rewritten form of (8.29)  

However, from the general Gibbs-Helmholtz equation (5.56), we can write 

As shown in (8.34b, c), the T dependence of Keq is governed solely by the heat of reaction AH° under constant-P conditions. 

The Van t Hoff equation (8.34c) can also be expressed in graphical form. If we plot values of ln eq versus 1/7, (8.34c) establishes that the slope of the curve is —AH°/R. In many cases, the variation of AH° with temperature is slight, so that 

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