What does Gibbs free energy (G) measure?

Gibbs free energy (G) is a key concept in thermodynamics that quantifies the maximum reversible work that can be performed by a system at constant temperature and pressure. This is significant because it helps determine the spontaneity of a reaction.

When considering a chemical reaction, if the change in Gibbs free energy (ΔG) is negative, the process can occur spontaneously, meaning it can proceed without the input of extra energy. Conversely, if ΔG is positive, the reaction is non-spontaneous under those conditions and would require energy input to proceed. This relationship between Gibbs free energy and the capability to do work is vital in various applications, including chemical reaction engineering and biochemistry.

The other options do not accurately reflect the scope of Gibbs free energy. For instance, while total energy change refers to the overall energy change during a reaction, it does not specifically address the conditions of constant temperature and pressure or the reversibility of work. Similarly, activation energy focuses on the energy required to initiate a reaction, not the thermodynamic feasibility after it has started. Finally, the energy lost during a chemical reaction may not fully encapsulate the concept of Gibbs free energy, as it is not just a measure of energy loss but also reflects system capability at