Octane, , combusts in air according to the equation with standard enthalpy change…

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

Octane, C8H18(l)\text{C}_{8}\text{H}_{18}(l), combusts in air according to the equation C8H18(l)+252 O2(g)→8 CO2(g)+9 H2O(l)\text{C}_{8}\text{H}_{18}(l)+\dfrac{25}{2}\,\text{O}_{2}(g)\rightarrow8\,\text{CO}_{2}(g)+9\,\text{H}_{2}\text{O}(l) with standard enthalpy change ΔHcomb=−5.48×103 kJ mol−1\Delta H_{\text{comb}}=-5.48\times10^{3}\,\text{kJ}\,\text{mol}^{-1}. (a) Determine the enthalpy change per gram of octane combusted. Report your answer to three significant figures. (b) A portable generator consumes 3.75 kg3.75\,\text{kg} of octane during a prolonged power outage. Calculate the total heat released, assuming complete combustion and standard conditions. (c) In an emergency heating scenario, liquid water at 25 ∘ ⁣C25\,^{\circ}\!\text{C} is to be converted entirely into steam at 100 ∘ ⁣C100\,^{\circ}\!\text{C} using the heat from octane combustion. The specific heat capacity of water is 4.18 J g−1 ∘ ⁣C−14.18\,\text{J}\,\text{g}^{-1}\,^{\circ}\!\text{C}^{-1} and the molar enthalpy of vaporization of water at 100 ∘ ⁣C100\,^{\circ}\!\text{C} is 40.7 kJ mol−140.7\,\text{kJ}\,\text{mol}^{-1}. Estimate the mass of water (in kilograms) that can be converted to steam by the heat released in part (b).

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