Ethanol ( ) is considered a renewable fuel

CHEMISTRY · Multi-part · AP · Chemistry · Thermochemistry · Thermochemistry

Problem

Ethanol (

C_{2}H_{5}OH

) is considered a renewable fuel. Standard enthalpies of formation at

298\,\text{K}

are provided in the table.

Substance	$\Delta H_f^\circ$ (kJ\,mol $^{-1}$ )
$C_{2}H_{5}OH(\ell)$	$-277.0$
$CO_{2}(g)$	$-393.5$
$H_{2}O(\ell)$	$-285.8$
$O_{2}(g)$	$0$

The balanced combustion reaction is

C_{2}H_{5}OH(\ell) + 3\,O_{2}(g) \to 2\,CO_{2}(g) + 3\,H_{2}O(\ell)

The density of liquid ethanol at

25^\circ\text{C}

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

. (a) Using the data in the table, calculate the standard enthalpy change,

\Delta H^\circ_{rxn}

, for the combustion of one mole of ethanol. (b) Determine the enthalpy change, in

\text{kJ g}^{-1}

, released by burning ethanol. (c) Calculate the minimum volume, in millilitres, of liquid ethanol that must be completely combusted to release

1.25 \times 10^3\,\text{kJ}

of energy. (d) State one assumption inherent in your calculation in part (c) and discuss how violating that assumption in a real engine could alter the actual energy released.

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