The activation energy of a reaction going on its own is 20 kJ. If the reaction was treated with a catalyst, which would most likely represent the amount of energy needed to start a reaction?

A catalyst lowers a reaction’s activation energy by providing an alternative pathway; it does not raise the energy needed to start the reaction. Starting from 20 kJ, the catalyzed reaction should therefore require less than 20 kJ. The choice of 15 kJ fits, while 20 kJ or more does not show a lowered activation energy.

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