Chapter 5.1, Problem 11P

Suppose that a hydrogen fuel cell, as described in the text, is to be operated at $75°C$ and atmospheric pressure. We wish to estimate the maximum electrical work done by the cell, using only the room–temperature data at the back of this book. It is convenient to first establish a zero–point for each of the three substances, $H_2$, $O_2$, and $H_{2}O$. Let us take G for both $H_2$ and $O_2$ to be zero at $25°C$, so that G for a mole of $H_{2}O$ is –237 kJ at $25°C$.

(a) Using these conventions, estimate the Gibbs free energy of a mole of $H_2$ at $75°C$. Repeat for $O_2$ and $H_{2}O$.

(b) Using the results of part (a), calculate the maximum electrical work done by the cell at $75°C$, for one mole of hydrogen fuel. Compare to the ideal performance of the cell at $25°C$.