# Physical Chemistry- Using the integrated Vant Hoff Equation with K values.

Twickel

## Homework Statement

The equilibrium concentration of oxygen in fresh water exposed to the atmosphere is given for two temperatures. At 15 degrees celcius equilib [O2]= 630μmol/L at 25 degrees celcius equiln [O2]= 517μmol/L

The expression for the equilibrium constant, K, between the oxygen in the gas phase and in solution is given by K=[O2]/PO2/atm. Where pO2 is the partial pressure of atmospheric oxygen.

I need to calculate the enthalpy of dissolution, I figured I need to use the integrated Vant hoof equation.
But how do I figure out the partial pressues of oxygen so I can calculate the equilibrium constants?

[Thank you

## Answers and Replies

Gold Member
Partial pressure of oxygen is the fraction of pressure exerted by atmospheric oxygen. And since the Partial pressure is not going to change whether the oxygen dissolves or not, you don't require the use of oxygen's partial pressure.

You may write simply, K = [O2]. Now just use Van't Hoff's Equation.

Twickel
Thanks.

I do not understand why I don't have to use the partial pressure, when it is in the expression for Kp. Is this the case for any equilibrium constant involving kp=[x]/Po2/atm?