An electrochemical cell is fueled by the combustion of butane at \( 1 \, \text{bar} \) and \( 298 \, \text{K} \). Its cell potential is \( \dfrac{X}{F} \times 10^{3} \) volts, where \( F \) is the Faraday constant. The value of \( X \) is __________.
Use: Standard Gibbs energies of formation at \( 298 \, \text{K} \) are: \( \Delta_f G^\circ_{\text{CO}_2} = -394 \, \text{kJ} \, \text{mol}^{-1}; \; \Delta_f G^\circ_{\text{water}} = -237 \, \text{kJ} \, \text{mol}^{-1}; \; \Delta_f G^\circ_{\text{butane}} = -18 \, \text{kJ} \, \text{mol}^{-1} \).
