Thermodynamics

Thermodynamics

Question

The enthalpies of combustion of carbon and carbon monoxide are -393.5 and -283 kJ mol-1 respectively. The enthalpy of formation of carbon monoxide per mole is

  • 110.5 kJ

  • -110.5 kJ

  • -676.5 kJ

  • 676.5 kJ

Answer

B.

-110.5 kJ

left parenthesis straight I right parenthesis space straight C space left parenthesis straight s right parenthesis space plus space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards arrow with space space on top space CO subscript 2 space left parenthesis straight g right parenthesis end subscript space space semicolon space increment straight H space equals space minus space 393.5 space kJ
left parenthesis II right parenthesis space CO space left parenthesis straight g right parenthesis space plus space 1 half space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards arrow for space space of space CO space left parenthesis straight g right parenthesis space semicolon space increment straight H space equals space minus 283.0 kJ
substracting space left parenthesis straight I right parenthesis space from space left parenthesis II right parenthesis
left parenthesis III right parenthesis space straight C left parenthesis straight s right parenthesis space plus space 1 half space straight O subscript 2 space left parenthesis straight g right parenthesis space rightwards arrow with space space space on top space CO space left parenthesis straight g right parenthesis space increment straight H space equals space minus space 110.0 space kJ
This equation (III) also represents formation of ore mole of CO and thus enthalpy change is the heat formation of CO (g)

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