An equilibrium between hydrogen and nitrogen to make ammonia. Explain what would happen to the amount of product if a) pressure was increased b) temperature was increased c) a catalyst was added. Energy change -92KJ/mol

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This is quite a complicated sounding question but it is actually quite simple if you break it down! Start by writing a balanced equation for the reaction:

3H2 (g) + N2 (g) => 2NH3 (g)

Now you can see there is four molecules on the left and two on the right, which will help with the answer. It is a good habit to always write your state symbols, especially when this question mentions pressures.

Remember causing a change in the conditions of an equilibrium results in changes to get the equilibrium back to normal.

a) An increase in pressure will cause the amount of product to increase. The equilibrium will shift to the right where there are fewer molecules in order to counteract the change, and decrease the pressure.

b) The reaction is exothermic, which means it has a negative enthalpy change, ie it gives out heat. The amount of product will decrease. The equilibrium will move to the left in the endothermic direction in order to cool the reaction, so less ammonia is produced.

c) This is a bit of a trick question! Think about it: a catalyst basically speeds up a reaction. If the reaction is at equilibrium, the catalyst will simply speed up the reaction in both directions, and not have an affect on the amount of product formed, but just cause the product to be formed more quickly.

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