What will be the heat of formation of methane, if the heat of combustion of carbon is '-x' kJ, heat of formation of water is '-y' kJ heat of combustion of methane is '-z' kJ?

Options

A. `(-x-y+z)kJ`
B. `(-x-y+z)kJ`
C. `(-x-2y-z)kJ`
D. `(-x-2y+z)kJ`

Answer

D

Explanation

`{:((I)C+O_(2)rarrCO_(2),DeltaH=-xkJ),((II)H_(2)+(1)/(2)O_(2)rarrH_(2)O,DeltaH=-y kJ),((III)CH_(4)+2O_(2)rarrCO_(2)+2H_(2)O,DeltaH=-zkJ):}`
Multiply Eq. (II) by 2, adding to (I) and then, subtract Eq. (III) from the sum
`C+2H_(2)rarrCH_(4)" "DeltaH=(-x-2y+z)kJ`