Question

The efficiency of a fuel cell is given by:
[1 Mark]

• A. $\frac{\Delta G}{\Delta S}$
• B. $\frac{\Delta G}{\Delta H}$
• C. $\frac{\Delta S}{\Delta G}$
• D. $\frac{\Delta H}{\Delta G}$

Answer 1

The correct option is B $\frac{\Delta G}{\Delta H}$

The thermal efficiency, h of a fuel conversion device is the amount of useful energy produced relative to the change in enthalpy, $\Delta H$ between the product and feed streams.
$\eta =\frac{\text{Useful energy}}{\Delta H}$
In an ideal case of an electrochemical converter, such as a fuel cell, the change in Gibb’s free energy, $\Delta G$ of the reaction is available as useful electric energy at that temperature of the conversion.
Hence,
${\eta }_{ideal}=\frac{\Delta G}{\Delta H}$