The enthalpy of combustion of carbon and carbon monoxide are −393.5 and −283kJ/mol respectively. The enthalpy of formation of carbon monoxide per mole is:
A
110.5kJ
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B
676.5kJ
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C
−676.5kJ
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D
−110.5kJ
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Solution
The correct option is D−110.5kJ I: C(s)+O2(g)→CO2;ΔH1=−393.5kJ/mol
II: CO(g)+12O2(g)→CO2(g);ΔH2=−283.0kJ/mol
On substracting II from I we get the formation reaction of carbon monoxide.
III: C(s)+12O2(g)→CO(g);ΔH=ΔH1−ΔH2=−110.5kJ/mol
This equation III represents the formation of 1 mole of CO and thus enthalpy of formation of CO(g) is −110.5kJ/mol.