The combustion of 5.00 g of C ₂ H ₆ (g) emits 259 kJ of heat at constant pressure. Calculate the enthalpy of combustion, Δ Hcom, for the reaction in kJ/g.
2 C₂H₆(g) + 7 O₂(g) → 4 CO₂(g) + 6 H₂O (l)

Question

Quizplus · Accepted Answer

The enthalpy of combustion ($\Delta H_{com}$) per gram is calculated by dividing the total heat emitted by the mass of the substance combusted. Given that the combustion of 5.00 g of the substance emits 259 kJ of heat, the enthalpy of combustion per gram is $\frac{259\ kJ}{5.00\ g} = 51.8\ kJ/g$. Since the process is exothermic (emits heat), the value is negative, making the correct answer $-51.8\ kJ/g$.

The Combustion of 5