Consider the following reaction:
`2NaN_(3)(s) rarr 2Na(s) +3N_(2)(g)`
The enthalpy change for this reaction at `1atm` is equal to:

Options

A. `-2Delta_(f)H^(Theta) [NaN_(3)(s)]`
B. `+2Delta_(f)H^(Theta)[NaN_(3)(s)]`
C. `3Delta_(f)H^(Theta)[N_(2)(s)+2Delta_(f)H^(Theta)(Na(s)]`
D. `-Delta_(f)H^(Theta)[NaN_(3)(s)]`

Explanation

`Delta_(f)H = DeltaH_(P) - DeltaH_(R)`
`[{:("Enthalpy of elements in their"),("stable state is assumed to be"),("zero".):}]`
`=(2 xx H_(Na) +3 xx H_(N_(2))) -2H_(NaN_(3))`
`=(2 xx 0+3 xx0) - 2H_(NaN_(3))`
`=- 2H_(NaN_(3))`