The reaction between hydrogen and nitrogen in the presence of an iron catalyst is known as the Haber process. It is a reversible reaction. The energy profile for this reaction is shown. What is the energy change when one mole of ammonia is decomposed into its component elements?

Answer:

10) A

The question states that the Haber process is reversible. The graph shows figures for when 2 moles of ammonia are formed. Overall, the reaction is exothermic with -92 kJ of energy released.
In the reverse process, 2 moles of ammonia decomposing into its elements would be endothermic and 92kJ of energy is absorbed.
The question, however, asks for when ONE mole of ammonia is decomposed. This would cause the amount of energy absorbed to halve, i.e. 92/2 = 46 kJ
So the answer is A.