## solving van't hoff equation

$\ln K = -\frac{\Delta H^{\circ}}{RT} + \frac{\Delta S^{\circ}}{R}$

hanna_maillard3B
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### solving van't hoff equation

what must remain constant in order to use the van't hoff equation ?

Chem_Mod
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### Re: solving van't hoff equation

For the traditional van't hoff equation where $lnK=-\frac{\Delta H}{RT} + \frac{\Delta S}{R}$ obviously R is constant, and assuming we know $\Delta H$ and $\Delta S$ at a given temperature T we can calculate K. If you are referring to the version of the van't hoff equation where you can convert between two K values at different temperatures, i.e. $ln(\frac{K_{2}}{K_{1}})=-\frac{\Delta H}{R}[\frac{1}{T_{2}}-\frac{1}{T_{1}}]$ then we are assuming that $\Delta H$ is constant at both temperatures so that it does not change and we can use it in our calculation (again R is also constant). To solve this equation you would need to be given at least 3 of the 4 variables, and it is most often used when given K1 at T1 and you are asked to find K2 at a given T2.