Past exam of the year 2 of the earth sciences (geology) course of the University of Oxford / 2024 / Paper 3 / 10 / ii / Solution

Subtract the nepheline–corundum reaction from the albite–corundum reaction and divide by two. In the albite-to-nepheline direction the resulting net reaction isAdditivity of the standard Gibbs energy of reaction makes the logarithms of the equilibrium constants combine with the same coefficients:This normalization is per one albite formula unit. The doubled reaction has ${\log }_{10}K=-22.06$, and reversing the reaction changes its sign.