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[smurphy1D]

What is an intermediate in a reaction and how can you tell when they occur? For example this problem shows a graph and states there are 2, but how can I tell?

[Junwei Sun 4I]

An intermediate is a substance that is created by one elementary step and further react with other substances to give the final products. The graph shows that there are two intermediates because there're three steps in total, so the first two elementary steps must have produced some forms of intermediates that reactive to produce the final products.

[smurphy1D]

Thanks! So would I then be able to tell if a catalyst is involved if i am able to spot an intermediate just from the graph?

[jisulee1C]

An intermediate and catalyst are not the same thing as in an intermediate is produced and used up during the reaction while a catalyst is not used up in the reaction. You can tell if a catalyst is used if the activation energy is lower than before, you are assuming the intermediate steps involve catalysts if the overall activation energy is less than if there were the intermediate steps.