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Change in enthalpy and change in interna...

Change in enthalpy and change in internal energy are state functions. The value of `DeltaH, DeltaU` can be determined by using Kirchoff's equation.
Calculate the heat of formation of methane, given that heat of formation of water `= -286kJ mol^(-1)`, heat of combustion of methane `= -890kJ mol^(-1)` heat of combustion of carbon `= -393.5 kJ mol^(-1)`

A

`90.5 kJ mol^(-1)`

B

`-240 kJ mol^(-1)`

C

`-75.5 kJ mol^(-1)`

D

`95.6 kJ mol^(-1)`

Text Solution

Verified by Experts

The correct Answer is:
C
`CH_(4) + 2O_(2) rarr CO_(2) + 2H_(2)O`
`Delta H = Delta H_(f_(CO_(2))) + 2Delta H_(f_(H_(2)O)) - Delta H_(f_(CH_(4)))`
`Delta H_("Combustion"_(CH_(4))) = Delta H_("combustion"_(( C))) + 2 Delta H_(f_(H_(2)O)) - Delta H_(f_(CH_(4)))`
`-890 = -393.5 + 2 xx (-286) - Delta H_(f_(CH_(4)))`
`Delta H_(f_(CH_(4))) = - 75.5` kJ/mol
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