If one mole of ammonia and one mole of hydrogen chloride are mixed in a closed container to form ammonium chloride vapor, then

Options

A. `Delta H = Delta U`
B. `Delta H gt Delta U`
C. `Delta H lt Delta U`
D. there is no relationship

Answer

C

Explanation

Themochemical equation is
`NH_(3) (g) + HCl (g) rarr NH_(4) Cl_(g)`
Accroding to thermodynamics,
`Delta H = Delta U + Delta n_(g) RT`
where `Delta n_(g) = sum n_(P) (g) - sum n_(R ) (g)`
`= (1) - (1 + 1)`
`= -1`
Since `Delta n_(g)` is negative `(lt 0)` we conclude that `Delta H lt Delta U`