when an enzyme binds with its subsrate, the activation energy needed for the chemical reaction to occur is rai

Answer 1

high level of enthalpy.

I'm not sure what rai is, but the product must create more enthalpy for an irreversible reaction

Answer 2

the activation energy required for the reaction is lowered, the enzyme catalyses the reaction by lowering the activation energy, thus making the formation of a high energy intermediate favourable, and thereby increasing the rate or probability of reaction to occur