Understanding the Relationship between Enthalpy and Entropy in Gibbs Free Energy


Enthalpy and entropy are two important thermodynamic concepts that help us understand and predict the behaviour of substances in various physical and chemical processes. They are both components of the Gibbs free energy formula, which is a fundamental equation in thermodynamics. The relationship between enthalpy and entropy is crucial in determining whether a process is thermodynamically favorable or not.

Enthalpy, denoted as H, is a measure of the total energy of a system at constant pressure. It takes into account the internal energy of the system and the work done by or on the system. In other words, enthalpy represents the energy available to do work. It is a state function, meaning it depends only on the current state of the system and not the path it took to get there.

Entropy, denoted as S, is a measure of the randomness or disorder of a system. It is a state function that increases with the probability of a given state occurring. In simpler terms, entropy is a measure of the systems’ tendency to spread out and disperse energy evenly. It is often described as the measure of the “disorder” or “chaos” in a system.

Now, how do enthalpy and entropy relate to each other in the context of Gibbs free energy? The Gibbs free energy formula is given as G = H – TS, where T is the temperature in Kelvin and S is the entropy of the system. This formula is important because it helps us understand whether a process is thermodynamically favorable or not.

When discussing enthalpy and entropy, it is essential to understand the concept of spontaneity. A spontaneous process is one that occurs without any external influence or intervention. In contrast, a non-spontaneous process needs external work to occur.

If a process has a negative value for ΔG, it is considered spontaneous, and if it has a positive value, it is considered non-spontaneous. When ΔG = 0, the process is at equilibrium, meaning there is no net change in the system. The relationship between enthalpy and entropy plays a vital role in determining the spontaneity of a process.

From the definition of Gibbs free energy, we can see that entropy has a direct relationship with the spontaneity of a process. As entropy increases, the value of -TS in the formula decreases, making ΔG more negative and, therefore, making the process more spontaneous. However, enthalpy has an inverse relationship with spontaneity. As the enthalpy increases, the value of H in the formula becomes more positive, making the process less spontaneous.

This relationship between enthalpy and entropy is known as the compensation effect. If a process has a positive change in enthalpy (ΔH > 0), it must have a positive change in entropy (ΔS > 0) to be spontaneous. This is because the increase in entropy compensates for the decrease in enthalpy, making the overall free energy change negative. Similarly, if a process has a negative change in enthalpy (ΔH < 0), it must have a negative change in entropy (ΔS < 0) for it to be spontaneous. One example of this relationship can be seen in the melting of ice (H2O). The enthalpy change for melting ice is positive as energy is needed to break the intermolecular bonds holding the water molecules together. However, the process is spontaneous because there is a large increase in entropy as the water molecules become more disordered in the liquid phase. Understanding the relationship between enthalpy and entropy in Gibbs free energy is essential in predicting the spontaneity of processes and determining whether they are thermodynamically favorable. By considering both enthalpy and entropy changes, we can get a better understanding of the energetics and behavior of substances during physical and chemical processes.