Question

Which is correct for the combustion reaction occurring in an automobile is $2C_{8}H_{18}\left(\right.s\left.\right) \, + \, 25O_{2}\left(\right.g\left.\right) \, \, \rightarrow 16\left(CO\right)_{2}\left(\right.g\left.\right) \, + \, 18H_{2}O\left(\right.g\left.\right)$ .

• A. $\Delta H=-ve;\Delta S+ve;\Delta G=+ve$
• B. $\Delta H=+ve;\Delta S-ve;\Delta G=+ve$
• C. $\Delta H=-ve;\Delta S+ve;\Delta G=-ve$
• D. $\Delta H=+ve;\Delta S+ve;\Delta G=-ve$

Answer 1

Answer: (C)

By applying the Helmholtz equation: it shows the relationship between Change in enthalpy $\Delta H$, change in entropy $\Delta S \,\&\, $ change in free energy $\Delta G$
$\Delta G =\Delta H - T \Delta S$
$\Delta S =+\text{Ve}$ (Since moles of gases in the product are greater than that of the reactant) and
$\Delta H =$ $- Ve$ (Since, it is a combustion reaction)
$\Delta G =- Ve$ (Since temperature cannot be negative)