A reaction carried out under standard conditions has the following thermodynamic data: and

CHEMISTRY · Single correct · A Level · Chemistry · Electrode potentials · Electrode potentials

Problem

A reaction carried out under standard conditions has the following thermodynamic data:

E^\circ_{\text{cell}}=+0.15\,\text{V}

and

\Delta H^\circ=+50\,\text{kJ\,mol}^{-1}

. Which conclusion about the spontaneity of the reaction at

25\,^{\circ}\text{C}

is most justified? (a) The reaction is non-spontaneous because its positive

\Delta H^\circ

overrides the positive

E^\circ_{\text{cell}}

. (b) No firm conclusion can be drawn without the value of

\Delta S^\circ

, since the positive

\Delta H^\circ

may offset a favorable

E^\circ_{\text{cell}}

. (c) The reaction is spontaneous because

E^\circ_{\text{cell}}

is positive, so

\Delta G^\circ=-nF E^\circ_{\text{cell}}<0

even though

\Delta H^\circ

is positive. (d) The reaction is non-spontaneous because a positive cell potential means work must be done on the system (

\Delta G^\circ = +nF E^\circ_{\text{cell}}>0