Question

When nitrogen gas reacts with hydrogen gas to form ammonia, 92.38 KJ of heat are given off for each mole of nitrogen gas consumed, under constant pressure and standard conditions. What is the value of H degree for the reverse of the reaction shown.?

Answer 1

The value of `DeltaH` for the reverse reaction = +92.38kJ

`N_(2(g))+3N_(2(g))rarr2NH_(3(g))`

For which `DeltaH=-92.38"kJ"`

The minus sign signifies that heat is given out to the surroundings i.e. the reaction is exothermic

If we write the reverse reaction:

`2NH_(3(g))rarrN_(2(g))+3H_(2(g))`

Then heat must be taken in from the surroundings and the reaction is endothermic.

So we reverse the sign `rArr`

`DeltaH = +92.38"kJ"`