A reversible reaction is one where A) there are large changes in the net free energy from substrate to product. B) there is little change in the net free energy between substrate and product. C) there is no change in the net free energy from substrate to product. D) a reaction is unlikely due to the high activation energy.

A reversible reaction is one where B) there is little change in the net free energy between substrate and product.

Explanation:

A reversible reaction is one that reagents are transformed into products and at the same time products are transformed into reagents. That is to say that as the products appear in the reaction, they can react with each other by regenerating the reagents again. It is represented by a double arrow, indicating that the reaction can be carried out both in one direction and the other way around.

At the start of the reaction, there is a large amount of reagents. As time goes by, that amount decreases and speed too.

On the other hand, at the beginning of the reaction there are no products. As the reaction happens, the products are being formed and their speed will increase to match the speed of the reagents. When the rates of products and reagents are equal and constant, it is possible to say that the reaction is in chemical equilibrium. At this point, both reactions continue to happen, but the total concentrations of reagents and products no longer change.

The Gibbs free enthalpy or free energy of a system is a measure of the amount of usable energy (energy that a job can perform) in that system.

When a reaction system is in chemical equilibrium, it is in the lowest possible energy state (it has the lowest possible free energy). If a reaction is not in equilibrium, it will move spontaneously towards it because that allows it to reach a state of lower and more stable energy. Then when the reaction moves towards equilibrium, the free energy of the system decreases more and more.

Finally, a reversible reaction is one where B) there is little change in the net free energy between substrate and product.