Consider the decomposition of ammonia into molecular hydrogen and nitrogen: 2NH3
ID: 861487 • Letter: C
Question
Consider the decomposition of ammonia into molecular hydrogen and nitrogen: 2NH3(g) ?? ?? N2(g) + 3H2(g)
a. Calculate the change in enthalpy for the reaction at standard conditions from bond dissociation energies. See the appendix for the table of bond energies.
b. Name two things that you could do to favor the formation of ammonia by this reaction.
c. Using the value of ?H calculated in 2a, is this an exothermic or endothermic reaction? Explain your answer.
d. This reaction has a very large activation energy. Name one thing you could do to increase the rate of this reaction.
Explanation / Answer
Delta H of reaction = Sum of B.E of Reactants - Sum of B.E of products
Delat H = 6 X (B.E. of N-H ) - [B.E. N?N + 3X B.E.H-H ] = 6 X 389 - [946 + 3X 436] = 80KJ
H-H : 436
H-N : 389
N?N : 946
2. The reaction is endothermic as the enthalpy is positive
3. the formation of ammonia will be exothermic so on decreasing temperature the formation of ammonia will be favoured, According to Le Chatelier's Principle, if you increase the pressure the system will respond by favouring the reaction which produces fewer molecules. That will cause the pressure to fall again, In order to get as much ammonia as possible in the equilibrium mixture, you need as high a pressure as possible.
4. use of catalyst