See the picture to answer the question the solid line is the results obtained when no catalyst was used and the broken line is the results obtained when a catalyst was used .how much energy must the system absorb for the reaction to start if no catalyst was used?

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

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