Question Video: Main Disadvantage of Increased Temperature in the Haber Process Chemistry

The Haber process involves the reversible reaction of two gaseous reactants. What is the main disadvantage of increasing the temperature at which the reaction is performed?

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Video Transcript

The Haber process involves the reversible reaction of two gaseous reactants. What is the main disadvantage of increasing the temperature at which the reaction is performed?

Haber process is an industrial method to produce ammonia via the reaction of nitrogen and hydrogen. Nitrogen and hydrogen are the two gaseous reactants referred to in the question. And this is the balanced equation for their reaction in the Haber process. The question asks what the main disadvantage of increasing the temperature is. Increasing the temperature of the reaction is always going to cost a little more. But that’s probably not going to be the main disadvantage referenced here. To solve this question, we’re going to need to recall what the entropy change of the reaction is, or at least what its sign is.

The entropy change for the forward reaction is negative, meaning the reaction of nitrogen and hydrogen is exothermic. It might interest you to know that the entropy change for the forward reaction is actually minus 92.4 kilo joules per mole. But we don’t need to know this value in order to answer the question. Le Chatelier’s principle says that, for a dynamic equilibrium, if the conditions change, the position of equilibrium will move to counteract the change. In this case, the change is an increase in temperature. For this reaction, since the forward reaction is exothermic, the reverse reaction must be endothermic. An endothermic reaction is a cooling process, which reduces the temperature. So increasing the temperature favors the reverse reaction.

So if we take our initial equilibrium and heat it up, our position of equilibrium will move to the left, favoring the reactants. So increasing the temperature reduces our equilibrium yield. So we get less ammonia at equilibrium. So the main disadvantage of increasing the temperature is that we reduce the maximum percentage yield.

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