Question

barrier? Can lowering the activation energy make a reaction go in either direction spontaneously? What if the concentrations of products and reactants were altered, making the reverse reaction a thermodynamically favored reaction. Could the enzyme function to speed up the reverse reaction in those circumstances?

Answer 1

1-

Activation Energy is the amount of energy produced to the reactant to start a reaction. Generally in case of Endothermic reactions, activation energy is given to start the reaction. And the product produced is obviously with lesser enegry than the reactants. And the reaction takes place in forward direction to make products.

For the reaction to go in either direction spontaneously means the reaction has reached in its equilibrium state. Thus the rate of forward reaction becomes equal to the rate of backward reaction. Now in this case Del G = zero.

So lowering activation energy wont result in achieving equilibrium

2-

Now when the reaction is reversed, and given the reaction becomes thermodynamically favorable. That means the reaction is spontaneous and does not require any activation energy to start. Even if it requires, the amount is small. Thus the activation energy is lowered.

In this case if we use a catalyst, then the role of catalyst is to increase the rate of the reaction thus by decreasing the activation energy. Once reaction starts due to catalyst and activation energy is already low, a time will come when the reaction will reach equilibrium. And here only the reaction will be spontaneous in either direction.