`delta_(f) U^(Ó¨) "of formation of" CH_(4)(g)` at a certain temperature is `-393Jmol^(-1).` The value of `delta H^(Ó¨)is:`

Options

A. zero
B. `lt Delta_(f) U^(Θ)`
C. `gt Delta_(f) U^(Θ)`
D. equal to `Delta_(f) U^(Θ)`

Answer

B

Explanation

The reaction is `CH_(4) (g) + 2O_(2) (g) rarr CO_(2) (g) + 2H_(2) O (l)`
`Deltan_(g) = (n_(p) - n_(r))_(g) = 1 - 3 = -2`
`Delta_(f) H^(-Θ) = Delta_(f) U^(Θ) + Delta n_(g) RT`
As `Delta n_(g) = -2`
`:. Delta_(f) H^(Θ) lt Delta_(f) U^(Θ)`