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. Gibbs free energy represents the usable energy released or absorbed by a reaction. To understand this concept further, let's break it down.

Gibbs free energy, also known as free enthalpy or G, is a thermodynamic potential that measures the maximum useful work that can be obtained from a system at constant temperature and pressure. It is named after the American scientist Josiah Willard Gibbs, who developed this concept.

Gibbs free energy takes into account both the enthalpy (total energy) and entropy (degree of disorder) of a system. It is calculated using the formula:

G = H - TS

Where:
- G is the Gibbs free energy
- H is the enthalpy (total energy) of the system
- T is the temperature in Kelvin
- S is the entropy (degree of disorder) of the system

Now, when considering a chemical reaction, the change in Gibbs free energy (∆G) determines whether the reaction will proceed spontaneously or not. If ∆G is negative, the reaction is exergonic, meaning it releases energy and is thermodynamically favorable. If ∆G is positive, the reaction is endergonic, meaning it requires an input of energy and is not thermodynamically favorable.

To determine the ∆G of a reaction, we use the equation:

∆G = ∆H - T∆S

Where:
- ∆G is the change in Gibbs free energy
- ∆H is the change in enthalpy
- ∆S is the change in entropy
- T is the temperature in Kelvin

By calculating ∆G, we can determine whether a reaction is spontaneous or requires external energy input. If ∆G is negative, the reaction will proceed spontaneously, releasing usable energy. If ∆G is positive, the reaction will not occur spontaneously and will require an input of energy.

In summary, Gibbs free energy helps us understand the thermodynamic feasibility and spontaneity of a chemical reaction by considering both the enthalpy and entropy changes in the system.

B. The usable energy released or absorbed by a reaction