The combustion of ethanol (C₂H₅OH) at 1 bar and 298 K releases 1367 kJ mol^-1 of heat.
C₂H₅OH (l) + 3 O₂ (g) $\rightarrow$ 2 CO₂ (g) + 3 H₂O (l) Calculate $\Delta_{c} U_{208}^{\prime}$ (in kJ mol^-1) for ethanol.

Question

The combustion of ethanol (C₂H₅OH) at 1 bar and 298 K releases 1367 kJ mol^-1 of heat.
C₂H₅OH (l) + 3 O₂ (g)

\rightarrow

2 CO₂ (g) + 3 H₂O (l) Calculate

\Delta_{c} U_{208}^{\prime}

(in kJ mol^-1) for ethanol.

Quizplus · Accepted Answer

The combustion of ethanol is an exothermic reaction, so the change in internal energy is negative. The enthalpy change is given by the heat released, so $\Delta_{c} H_{298}^{\prime}$ = -1367 kJ mol^-1. The change in internal energy is given by $\Delta_{c} U_{298}^{\prime}$ = $\Delta_{c} H_{298}^{\prime}$ - RT, where R is the gas constant and T is the temperature. Substituting the given values, we get $\Delta_{c} U_{298}^{\prime}$ = -1367 kJ mol^-1 - (8.314 J mol^-1 K^-1)(298 K) = -1365 kJ mol^-1.

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