`N_(2(g)) + 2O_(2(g)) rarr 2NO_(2) + xkJ, 2NO_((g)) + O_(2(g)) rarr 2NO_(2(g)) + ykJ`. The enthalpy of formation of NO is

Options

A. `(2x-2y)`
B. `x-y`
C. `1//2(y-x)`
D. `1//2(x-y)`

Answer

C

Explanation

`N_(2) + 2O_(2) rarr 2NO_(2), Delta H_(1) = -x`
`ul(2NO + O_(2) rarr 2NO_(2), Delta H_(2) = - y)`
`(1)/(2) N_(2) + (1)/(2) O_(2) rarr NO, Delta H = (Delta H_(1) - Delta H_(2))/(2)`
`= (-x + y)/(2)`