A) ? 6.2 kJ
B) ? 37.4 kJ
C) ? 35.5 kJ
D) ? 20.0 kJ
Correct Answer: B
Solution :
\[C+{{O}_{2}}\to C{{O}_{2}}\,;\,\,\,\Delta {{H}_{F}}=-490\,KJ/mol\] ? (I) \[{{H}_{2}}+1/2{{O}_{2}}\to {{H}_{2}}O;\,\,\Delta {{H}_{F}}=-240\,KJ/mol\] ? (II) \[8C+18H\to {{C}_{8}}{{H}_{18}};\,\,\Delta {{H}_{F}}=+160KJ/mol\] ? (III) applying (I)\[\times \,8+\] (II) \[\times 9+\](III) \[{{C}_{8}}{{H}_{18}}+\frac{25}{2}{{O}_{2}}\to 8C{{O}_{2}}+9{{H}_{2}}O\] \[\Delta {{H}^{o}}=-3920-2160-160=6240\,KJ/mol\] \[\Delta {{H}^{o}}=\] for 6 moles of octane \[=6240\times 6\] \[=37440\,KJ/mol=-37.4\,KJ\]
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