Example on the roasting of galena

For the purpose of illustrating the principles discussed above it is of interest to calculate the equilibrium constant of the reaction 

The free energies of formation at 25 C, and the enthalpies of formation at 18 are as follows  

Assuming the gas phase to be perfect, the partial equilibrium constant 

At 25 using the data on the free energies of formation, we obtain 

Equations for the molar heat capacities of a number of gases have been collected by Spencer.f The equations for oxygen and sulphur dioxide are 

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