ThermochemistryHard

Question

Determine ᐃUo at 300 K for the following reaction using the listed enthalpies of reaction :
4CO(g) + 8H2(g) → 3CH4 (g) + CO2(g) + 2H2O(l)
C(graphite) + 1/ 2O2(g) → CO(g); ᐃH1o = - 110.5 kJ
CO(g) + 1/ 2O2(g) → CO2(g); ᐃH2o = - 282.9 kJ
H2(g) + 1/ 2O2(g) → H2O(l); ᐃH3o = -285.8 kJ
C (graphite) + 2H2(g) → CH4(g); ᐃH4o = -74.8 kJ

Options

A.-653.5 kJ
B.-686.2 kJ
C.-747.4 kJ
D.None of these

Solution

ᐃHo = - 3ᐃHo1 + ᐃHo2 + 2ᐃHo3 + 3ᐃHo4
= - 747.4 kJ
ᐃHo = ᐃUo + ᐃng RT; where ᐃng = - 8
- 747.4 = ᐃUo -
ᐃUo = - 727.44 kJ.

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