δg = δh - tδs

Definition

The equation δg = δh - tδs represents the Gibbs free energy change of a system, where δg is the change in free energy, δh is the change in enthalpy, t is the temperature in Kelvin, and δs is the change in entropy. This equation is crucial for understanding how spontaneous processes occur, as it relates thermodynamic properties to determine whether a reaction can proceed without external energy input. It highlights the balance between energy and disorder, showing that a decrease in free energy indicates a favorable reaction.

5 Must Know Facts For Your Next Test

1. A negative value of δg indicates that a reaction is spontaneous under constant temperature and pressure conditions.
2. The term 'tδs' shows how temperature influences the spontaneity of a process; at higher temperatures, entropy changes become more significant.
3. In cases where δh is positive (endothermic reactions), spontaneity may still occur if δs is significantly positive, leading to a negative δg.
4. The Gibbs free energy change can be used to calculate the equilibrium constant for a reaction, linking thermodynamics with chemical equilibria.
5. For systems at equilibrium, δg equals zero, indicating that there is no net change in the system over time.

Review Questions

• How does the relationship between δg, δh, and δs help determine whether a reaction will occur spontaneously?
  • The relationship described by the equation δg = δh - tδs helps determine spontaneity by showing how changes in enthalpy and entropy contribute to free energy. If the free energy change (δg) is negative, it means that the reaction can occur spontaneously. This relationship emphasizes that both the heat content and disorder of a system must be considered together when predicting if a reaction will proceed without external input.
• Discuss how temperature influences the spontaneity of reactions as indicated by the equation δg = δh - tδs.
  • Temperature plays a critical role in determining spontaneity as reflected in the equation. The term 'tδs' suggests that at higher temperatures, even processes with positive enthalpy changes (δh) might become spontaneous if they also have sufficiently large positive entropy changes (δs). Thus, increasing temperature can shift the balance toward negative free energy changes, allowing reactions that are endothermic to proceed spontaneously under certain conditions.
• Evaluate how this equation links thermodynamic concepts to practical applications in chemistry and engineering.
  • This equation serves as a foundational concept in both chemistry and engineering by linking thermodynamic principles to real-world applications. For instance, it can be used to predict whether industrial chemical reactions will happen under given conditions, which is essential for designing reactors and optimizing processes. Furthermore, understanding this relationship allows chemists to manipulate conditions such as temperature and pressure to favor desired reactions, thus enhancing efficiency and sustainability in chemical production.

Related terms

Enthalpy (δh): A thermodynamic quantity that represents the total heat content of a system, indicating how much energy is absorbed or released during a process at constant pressure.

Entropy (δs): A measure of the disorder or randomness in a system; higher entropy means greater disorder and more possible microstates.

Spontaneity: The tendency of a process to occur without outside intervention, determined by the sign of the Gibbs free energy change (δg).