Above is a potential energy curve of a reaction. It depicts conversion of reactant to product via transition state.
When a catalyst is added to the reaction system, energy barrier of reaction decreases.
It must be noted that energy barrier reaction is defined as energy difference between  reactant and transition state.
In present case, energy of reactant is 200 kj, while that of transition state (in absence of catalyst) is 650 kj
Thus, energy barrier of reaction is 650 - 200 = 450 kj
Hence, system must absorb 450 kj of energy for the reaction to start, if no catalyst was used
