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The heat of formations for CO(2)(g),H(2)...

The heat of formations for `CO_(2)(g),H_(2)O(l) and CH_(4)(g)` are -400 kJ `mol^(-1),-280" kJ "mol^(-1) and -70" kJ "mol^(-1)`, respectively. The heat of combustion of `CH_(4)` in kJ `mol^(-1)` is

A

800

B

`-160`

C

`-890`

D

`-90`

Text Solution

Verified by Experts

The correct Answer is:
C
`DeltaH_("reaction") = sum Delta H_(f)`product - `sum DeltaH_(f)` recatant
`DeltaH_(f)` of a single element `O_(2), H_(2), Cl_(2)` is considered euqal to zero.
`CH_(4) + 2O_(2) to CO_(2) + 2H_(2)O`
`Delta H_("reaction") = Delta H_(f) (CO_2) + 2DeltaH_(f) cdot (H_2O) - Delta H_(f) (CH_4)-2DeltaH_(f) (O_2)`
`=-400 + 2(-280) - (-70-0) = -890 kJ mol^(-1)`.
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