which reaction will occur in the shortest amount of time. So shortest amount of time really means which chemical reaction is fastest. So remember we talked earlier about speed and activation energy if we want the fastest chemical reaction, Well, that would mean that we want the lowest activation energy if we take a look here. Reaction A is 1 43 killer jewels Reaction be as 80 killer jewels and reactions. C is 215 killer jewels. The answer is B. Since it has the lowest activation energy, that would mean that it moves the fastest and therefore would have the shortest amount of time necessary to go to completion.