The standard enthalpy change upon dissolving one mole of

Chapter 5, Problem 89P

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Problem 89P

The standard enthalpy change upon dissolving one mole of oxygen at 25°C is −11.7 kJ. Use this number and the van’t Hoff equation (below Problem) to calculate the equilibrium (Henry’s law) constant for oxygen in water at 0°C and at 100°C. Discuss the results briefly.

Problem:

Derive the van’t Hoff equation,

which gives the dependence of the equilibrium constant on temperature. Here ΔH° is the enthalpy change of the reaction, for pure substances in their standard states (1 bar pressure for gases). Notice that if ΔH° is positive (loosely speaking, if the reaction requires the absorption of heat), then higher temperature makes the reaction tend more to the right, as you might expect. Often you can neglect the temperature dependence of ΔH°; solve the equation in this case to obtain