What is Gibbs free energy?

A. The energy lost as heat to the surrounding molecules
B. The usable energy released or absorbed by a reaction
C. The energy in the form of kinetic energy in a system
D. The energy contained within the bonds of molecules

The correct answer is B. The Gibbs free energy is the usable energy released or absorbed by a reaction. To understand why this is the correct answer, let me explain how to approach this question.

To determine the Gibbs free energy, it's important to understand that it is a thermodynamic property that relates to the spontaneity and equilibrium of a chemical reaction. The Gibbs free energy (G) is defined as the energy available to do useful work in a system at constant temperature and pressure.

To calculate the Gibbs free energy of a reaction, you need to know the change in enthalpy (ΔH) and the change in entropy (ΔS) for the reaction. The equation for Gibbs free energy is:

ΔG = ΔH - TΔS

Where:
- ΔG is the change in Gibbs free energy
- ΔH is the change in enthalpy (heat released or absorbed) of the reaction
- ΔS is the change in entropy (degree of disorder) of the reaction
- T is the temperature in Kelvin

If ΔG is negative, it indicates that the reaction is spontaneous and exergonic (releases energy). This means that the reaction proceeds forward on its own and can do useful work. On the other hand, if ΔG is positive, the reaction is non-spontaneous and endergonic, meaning it requires an input of energy to occur.

Therefore, option B is the correct answer. Gibbs free energy represents the usable energy released or absorbed by a reaction, and it is a key concept in understanding the energetics of chemical reactions.

B. The usable energy released or absorbed by a reaction