Liquid ethanol combusts completely in oxygen according to the equation

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

Problem

\mathrm{C_2H_5OH(l) + 3\,O_2(g) \rightarrow 2\,CO_2(g) + 3\,H_2O(l)}

. Thermodynamic data (standard conditions):

Substance	Energy value
$\mathrm{C_2H_5OH(l)}$	$-277.7\,\text{kJ}$ for $0.500\,\text{mol}$
$\mathrm{CO_2(g)}$	$-393.5\,\text{kJ\,mol}^{-1}$
$\mathrm{H_2O(l)}$	$-285.8\,\text{kJ\,mol}^{-1}$

Density of liquid ethanol:

0.789\,\text{g\,mL}^{-1}

. (a) Convert the energy value given for liquid ethanol to a molar standard enthalpy of formation, in

\text{kJ\,mol}^{-1}

. (b) Calculate the standard enthalpy change, in kJ, for the combustion reaction as written. (c) Determine the standard enthalpy change, in kJ, associated with burning exactly

1.00\,\text{L}

of liquid ethanol under standard conditions. Include density and molar-mass calculations. (d) Discuss two practical factors that could cause the actual heat released in a real-world combustion device to differ from the value calculated in part (c).

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