The synthesis of ammonia is an exothermic process..?

Question

the synthesis of ammonia is an exothermic process: N2 +3H2 --> 2NH3 (delta triangle)H= -91.8 kJ, the ethalpy of the decomposition of ammonia would be?

a. +91.8 kJ

b. -91.8 kJ

c. +183.6 kJ

d. -183.6 kJ

Answer 1

The enthalpy change for the reverse process is the negative of the enthalpy change for the forward process.  Thus, in this case, it will be positive 91.8 kJ, choice a.

This assumes you are decomposing 2 moles of NH3, the same number that was formed in the forward reaction.