Reactant a can participate in both of these reactions:
1) a + b c + d grxn = –15.6 kj
2) a + e f + g grxn = –20.5 kj
reaction 1 has a much higher rate than reaction 2 under the same reaction conditions. explain this observation in terms of activation energy.

The activation energy is the amount of energy required to initiate a certain reaction. The activation energy may considered as an "energy barrier" that has to be overcome in order for a reaction to begin. If a reaction has a lower activation energy, then it will occur more easily and at a faster rate than a reaction with a higher activation energy. Therefore, the reason that reaction 1 is faster than reaction 2 is because it has a lower activation energy than reaction 2.