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The
individual formation reactions for the substances appearing in the
combustion process and their molar heats of formation, DHo298
are:
1. 2C(s) + 3H2(g) + �O2(g)
� C2H6OH(l)
-66.4 kcal
2. O2(g) �
O2 (g) (already in standard state) 0
3. C(s) + O2(g) �
CO2(g) -94.1
kcal
4. H2(g) + �O2(g)
� H2O(l)
-68.3 kcal
The standard state for carbon is solid graphite, and that for all
other elements on the left side of the equations is the gas at one
atmosphere.
The superscript zero on DH indicates
standard states for reactants and products, and the subscript 298
(often omitted and assumed) indicates that the heats quoted are
for reactions begun at 298K, with the products brought back to the
starting temperature at the conclusion of the reaction.
The heats are expressed, as they usually are, as kilocalories per
mole of compound formed. Values for some representative substances
are shown in this
table.
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