What is the physical significance of a negative Gibbs free energy change?

A negative Gibbs free energy change signifies that a reaction is spontaneous and will occur without external input.

In more detail, the Gibbs free energy change, denoted as ΔG, is a thermodynamic potential that measures the maximum reversible work that a system can perform at constant temperature and pressure. It is named after Josiah Willard Gibbs, who introduced it in the 19th century. The Gibbs free energy change is a crucial concept in thermodynamics and is used to determine whether a chemical reaction will occur spontaneously.

If ΔG is negative, it means the reaction is exothermic and energy is released, making the reaction spontaneous. This is because the system is moving from a higher energy state to a lower energy state, which is a more stable state. The system does not need any external energy to proceed, and it will continue until it reaches equilibrium.

On the other hand, if ΔG is positive, the reaction is endothermic and energy is absorbed, making the reaction non-spontaneous. The system needs an external energy source to proceed. However, it's important to note that a non-spontaneous reaction can still occur under certain conditions, such as if there is a continuous supply of energy.

The value of ΔG also gives us information about the equilibrium of the reaction. If ΔG is zero, the reaction is at equilibrium, meaning the rate of the forward reaction equals the rate of the reverse reaction.

In summary, a negative Gibbs free energy change is a key indicator of a spontaneous reaction. It tells us that the reaction can occur without any external energy input, as the system is moving towards a more stable, lower energy state. This concept is fundamental in understanding the feasibility and spontaneity of chemical reactions.