Question

According to Wikipedia: A chemical reaction is endergonic when non spontaneous. Thus in this type of reaction the Gibbs free energy increases.

My problem with that statement is the wording of non-spontaneous reactions. According to my knowledge, for every chemical reaction there is a ΔG, be it positive or negative, and is conncected to its equilibrium constant:

So in essence, if we only start with reactants, every reaction should yield some products, even if its ΔG is >0. Basically, every reaction is spontaneous to some extent. So is it only about semantics?

For example, in the biological context, even non-spontaneous reactions (with ΔG>0) can be driven to completion if its products are coupled to an exergonic reaction that consumes them and removes them from the endergonic equilibrium of the first reaction. That would mean that under those cirumstances the non-spontaneous reaction still produced some products (when starting with only reactants), is that right?

(What I also read though is that when stoechiometric molar quantities of reactants and products are mixed, more reactants are formed when ΔG is positive, so the reaction goes in the wrong direction.)

Answer 1

In a chemical reaction, exergonic reactions release energy and are spontaneous, while endergonic reactions absorb energy and are non-spontaneous. Although every chemical reaction has a ΔG value, not all reactions are spontaneous. Non-spontaneous reactions in biological systems can be driven forward by coupling them with exergonic reactions.

Step-by-step explanation:

A chemical reaction can be classified as exergonic or endergonic based on the change in Gibbs free energy (ΔG). In an exergonic reaction, the ΔG is negative, indicating that energy is released and the products have less free energy than the reactants. These reactions are spontaneous and can occur without the addition of energy.

On the other hand, in an endergonic reaction, the ΔG is positive, indicating that energy is absorbed and the products have more free energy than the reactants. These reactions are non-spontaneous, and they require an input of energy to occur.

While it is true that every chemical reaction has a ΔG value, it is important to note that not all reactions are spontaneous. Even though a reaction may have a positive ΔG, it can still occur under certain conditions. One example is in biological systems, where non-spontaneous reactions can be coupled with exergonic reactions to drive the overall process forward.

By coupling a non-spontaneous reaction with an exergonic reaction that consumes the products of the non-spontaneous reaction, the equilibrium can be shifted towards product formation. This allows the non-spontaneous reaction to proceed and produce products, even though it would not occur on its own.