Use the [latex]ΔH^{\circ}_{f}[/latex] data in Table 14.3 to calculate the value of [latex]ΔH^{\circ}_{rxn}[/latex] for the combustion of ethanol, [latex]CH_{3}CH_{2}OH(l)[/latex], at 25°C, described by the chemical equation [latex]CH_{3}CH_{2}OH(l) + 3\ O_{2}(g) → 2\ CO_{2}(g) + 3\ H_{2}O(l)[/latex]

Question 14.8: Use the ΔH°f data in Table 14.3 to calculate the value of ΔH......

Use the $ΔH^{\circ}_{f}$ data in Table 14.3 to calculate the value of $ΔH^{\circ}_{rxn}$ for the combustion of ethanol, $CH_{3}CH_{2}OH(l)$ , at 25°C, described by the chemical equation

CH_{3}CH_{2}OH(l) + 3\ O_{2}(g) → 2\ CO_{2}(g) + 3\ H_{2}O(l)

TABLE 14.3 standard enthalpies of formation, $ΔH^{\circ}_{f}$ , for various substances a 25°C
Substance	Formula	$ΔH^{\circ}_{f}/kJ\cdot mol^{-1}$	Substance	Formula	$ΔH^{\circ}_{f}/kJ\cdot mol^{-1}$
aluminum oxide	$Al_{2}O_{3}(s)$	-1675.7	hydrogen fluoride	$HF(g)$	-273.3
ammonia	$NH_{3}(g)$	-45.9	hydrogen iodide	$HI(g)$	+26.5
benzene	$C_{6}H_{6}(l)$	+49.1	hydrogen peroxide	$H_{2}O_{2}(l)$	-187.8
benzoic acid	$C_{6}H_{5}COOH(s)$	-385.2	iodine vapor	$I_{2}(g)$	+62.4
bromine vapor	$Br_{2}(g)$	+30.9	magnesium carbonate	$MgCO_{3}(s)$	-1095.8
butane	$C_{4}H_{10}(g)$	-125.7	magnesium oxide	$MgO(s)$	-601.6
calcium carbonate	$CaCO_{3}(s)$	-1207.6	magnesium sulfide	$MgS(s)$	-346.0
carbon (diamond)	$C(s)$	+1.897	methane	$CH_{4}(g)$	-74.6
carbon (graphite)	$C(s)$	0	methanol (methyl alcohol)	$CH_{3}OH(l)$ $CH_{3}OH(g)$	-239.2 -201.0
carbon (buckminster fullerene)	$C_{60}(s)$	+2327.0	methyl chloride	$CH_{3}Cl(g)$	-81.9
carbon dioxide	$CO_{2}(g)$	-393.5	nitrogen dioxide	$NO_{2}(g)$	+33.2
carbon monoxide	$CO(g)$	-110.5	nitrogen oxide	$NO(g)$	+91.3
carbon tetrachloride	$CCl_{4}(l)$ $CCl_{4}(g)$	-128.2 -95.7	dinitrogen tetroxide	$N_{2}O_{4}(g)$ $N_{2}O_{4}(l)$	+11.1 -19.5
chromium (III) oxide	$Cr_{2}O_{3}(s)$	-1139.7	octane	$C_{8}H_{18}(l)$	-250.1
cyclohexane	$C_{6}H_{12}(l)$	-156.4	pentane	$C_{5}H_{12}(l)$	-173.5
ethane	$C_{2}H_{6}(g)$	-84.0	propane	$C_{3}H_{8}(g)$	-103.8
ethanol (ethyl alcohol)	$CH_{3}CH_{2}OH(l)$	-277.6	sodium carbonate	$Na_{2}CO_{3}(s)$	-1130.7
ethene (ethylene)	$C_{2}H_{4}(g)$	+52.4	sodium oxide	$Na_{2}O(s)$	-414.2
ethyne (acetylene)	$C_{2}H_{2}(g)$	+227.4	sucrose	$C_{12}H_{22}O_{11}(s)$	-2226.1
freon-12 (dichloro difluoromethane)	$CF_{2}Cl_{2}(g)$	-477.4	sulfur dioxide	$SO_{2}(g)$	-296.8
glucose	$C_{6}H_{12}O_{6}(s)$	-1273.3	sulfur trioxide	$SO_{3}(g)$	-395.7
hexane	$C_{6}H_{14}(l)$	-198.7	tin(IV) oxide	$SnO_{2}(s)$	-577.6
hydrazine	$N_{2}H_{4}(l)$ $N_{2}H_{4}(g)$	+50.6 +95.4	water	$H_{2}O(l)$ $H_{2}O(g)$	-285.8 -241.8
hydrogen bromide	$HBr(g)$	-36.3
hydrogen chloride	$HCl(g)$	-92.3
Data from CRC Handbook of Chemistry and Physics, 86th Ed., Ed. David R. Lide, CRC Press, 2005–2006. (More thermodynamic data are given in Appendix D.)

Step-by-Step

The 'Blue Check Mark' means that this solution was answered by an expert.
Learn more on how do we answer questions.

Referring to Tables 14.2 and 14.3, we find that $ΔH^{\circ}_{f} [CO_{2}(g)] = -393.5\ kJ·mol^{-1}$ ; $ΔH^{\circ}_{f} [H_{2}O(l)] = -285.8\ kJ·mol^{-1}$ ; $ΔH^{\circ}_{f} [O_{2}(g)] =0$ ; and $ΔH^{\circ}_{f} [CH_{3}CH_{2}OH(l)] = -277.6\ kJ·mol^{-1}$ . Application of Equation 14.24 yields

$ΔH^{\circ}_{rxn} =ΔH^{\circ}_{f}\ [products] − ΔH^{\circ}_{f}\ [reactants]$ (14.24)

ΔH^{\circ}_{rxn} = \{ 2\ ΔH^{\circ}_{f} [CO_{2}(g)] + 3\ ΔH^{\circ}_{f} [H_{2}O(l)] \} – \{ΔH^{\circ}_{f} [CH_{3}CH_{2}OH(l)] + 3\ ΔH^{\circ}_{f} [O_{2}(g)]\} \\= \{2(–393.5\ kJ·mol^{–1}) + 3(–285.8\ kJ·mol^{–1})\} –\{(–277.6\ kJ·mol^{–1}) + 3(0\ kJ·mol^{–1})\} \\= –1366.8\ kJ·mol^{–1}

The ethanol combustion reaction is highly exothermic and is used extensively in alcohol burners of various types to keep food warm in chafing dishes (Figure 14.13). Ethanol is also used as a fuel and as an additive to gasoline mixtures.

TABLE 14.2 The states of representative elemental forms for which we take $\Delta H^{\circ}_{f} = 0$ at 25°c
Element	Formula
hydrogen	$H_{2}(g)$
oxygen	$O_{2}(g)$
nitrogen	$N_{2}(g)$
chlorine	$Cl_{2}(g)$
fluorine	$F_{2}(g)$
bromine	$Br_{2}(l)$
mercury	$Hg(l)$
sodium	$Na(s)$
magnesium	$Mg(s)$
carbon (graphite)	$C(s)$
sulfur (rhombic)	$S(s)$
iron	$Fe(s)$