Introduction to Gibbs Free Energy in Chemistry


When studying chemistry, we often come across the term Gibbs Free Energy, also known as Gibbs function or Gibbs energy. It is a fundamental concept in physical chemistry that is used to understand the spontaneity of a chemical reaction. In simple terms, Gibbs Free Energy is a measure of the energy available to do work in a system at a constant temperature and pressure.

Gibbs Free Energy, denoted by the symbol G, is named after the American scientist, J. Willard Gibbs, who first introduced this concept in the late 19th century. It is defined as the difference between the enthalpy (H) and the product of the temperature (T) and the entropy (S) of a system, multiplied by a constant known as the Boltzmann constant (K):

G = H – TS

Enthalpy represents the total energy of a system, including both the internal energy and the energy required to do work, while entropy is a measure of the randomness or disorder in a system. The Boltzmann constant is a constant value that relates the microscopic properties of individual particles to the macroscopic properties of a system. Together, these three variables – enthalpy, entropy, and temperature – determine the spontaneity of a reaction.

In chemistry, spontaneous reactions are those that occur naturally without any external influence or energy input. This means that they proceed on their own without the need for any additional energy. The concept of Gibbs Free Energy helps us determine whether a reaction is spontaneous or not.

According to the second law of thermodynamics, in any spontaneous process, the total entropy of the universe always increases. This means that for a chemical reaction to be spontaneous, the change in entropy (ΔS) of the system must be positive. In other words, the system must become more disordered as the reaction proceeds. However, this is not the only factor that determines the spontaneity of a reaction.

The change in enthalpy (ΔH) of a reaction can also affect its spontaneity. In an exothermic reaction, where the system releases energy in the form of heat, the ΔH value is negative. In this case, the reaction is spontaneous regardless of the sign of ΔS. On the other hand, in an endothermic reaction, where the system absorbs energy from its surroundings, the ΔH value is positive. In this case, the reaction is spontaneous only if the ΔS value is positive as well.

The relationship between ΔH, ΔS, and temperature (T) can be represented graphically by plotting them against each other in a graph known as a Gibbs Energy Diagram. The curve on this diagram, known as the Gibbs energy curve, represents the free energy change (ΔG) of a reaction. If this curve is above the x-axis, the reaction is not spontaneous, and energy must be input for the reaction to occur. If the curve is below the x-axis, the reaction is spontaneous, and energy is released during the process.

In summary, Gibbs Free Energy is a crucial concept in chemistry that helps us understand the spontaneity of a chemical reaction. It takes into account not only the change in entropy, but also the change in enthalpy and the temperature of a system. Through the Gibbs Energy Diagram, we can visualize and determine the spontaneity of a reaction, which is an essential factor in many industrial and biological processes.