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

Options

A. Zero
B. `lt Delta_(f) U^(Ɵ)`
C. `gt Delta_(f)U^(Ɵ)`
D. Equal to `Delta_(f)U^(Ɵ)`

Answer

B

Explanation

The reaction is `C(s) + 2H_(2)(g) rarr CH_(4)(g)`
`Delta n_(g)= 1-2= -1`
`Delta_(f)H^(Θ) = Delta_(f)U^(Θ) + Delta n_(g)RT`
As `Delta n_(g)= -1`
`therefore Delta_(f) H^(Θ) lt Delta_(f) U^(Θ)`