The relationship between free energy (G), enthalpy (H), and entropy (S) is described by the Gibbs free energy equation:
Δ G = Δ H – T Δ S
Let’s break down the relationships between these thermodynamic parameters:
1. Gibbs Free Energy (G):
Represents the maximum reversible work that a system can perform at constant temperature and pressure.
A negative Δ G indicates a spontaneous process (favorable for the process to occur), while a positive Δ G indicates a non-spontaneous process.
2. Enthalpy (H):
Represents the total heat content of the system.
A positive Δ H implies an endothermic process (heat is absorbed), while a negative Δ H implies an exothermic process (heat is released).
Enthalpy contributes to the direction of a process, and if Δ H is negative (exothermic), it favors spontaneity.
3. Entropy (S):
Represents the measure of disorder or randomness in a system.
A positive Δ S implies an increase in disorder, while a negative Δ S implies a decrease in disorder.
Entropy contributes to the spontaneity of a process, and if Δ S is positive, it favors spontaneity.
4. Temperature (T):
The absolute temperature in Kelvin.
The term -T Δ S reflects the temperature-dependent contribution to spontaneity.
Relationships
1. Spontaneity:
If Δ G < 0, the process is spontaneous, and both enthalpy and entropy contribute favorably to the spontaneity.
If Δ G > 0, the process is non-spontaneous, and both enthalpy and entropy contribute unfavorably to spontaneity.
2. Temperature Influence:
The term -T Δ S reflects the contribution of temperature to spontaneity.
At higher temperatures, the contribution of -T Δ S becomes more significant, making processes with positive Δ H and positive Δ S more likely to be spontaneous.
3. Enthalpy-Entropy Compensation:
Changes in enthalpy and entropy often interconnect. An exothermic process (negative Δ H) might involve a decrease in entropy (negative Δ S), and vice versa.
4. Equilibrium:
At equilibrium, Δ G = 0.
Equilibrium is achieved when the contributions of enthalpy and entropy are balanced.
In summary, the Gibbs free energy equation provides a comprehensive understanding of the thermodynamics of a process by considering both the heat content (enthalpy) and the degree of disorder (entropy) while accounting for the influence of temperature. It is a powerful tool for predicting the spontaneity and direction of chemical and physical transformations.
