δg = δh - tδs

Definition

The equation δg = δh - tδs describes the relationship between Gibbs free energy (δg), enthalpy (δh), and entropy (δs) at a given temperature (t). This equation helps determine the spontaneity of chemical reactions, indicating whether a process will occur naturally under specific conditions. When δg is negative, the reaction is spontaneous, while a positive δg suggests that the reaction is non-spontaneous, linking thermodynamic principles with reaction behavior.

5 Must Know Facts For Your Next Test

1. In the equation, δg represents the change in Gibbs free energy, which indicates the maximum amount of work that can be performed by a process at constant temperature and pressure.
2. The term δh signifies the change in enthalpy, reflecting heat absorbed or released during a reaction, while t is the absolute temperature in Kelvin.
3. Entropy change (δs) reflects the degree of disorder in the system; a positive δs indicates increased disorder, which often favors spontaneity.
4. If δg is zero, the system is at equilibrium, meaning there is no net change in concentration of reactants or products over time.
5. This equation highlights how both enthalpy and entropy contribute to a reaction's spontaneity: reactions that release heat and increase entropy are generally more likely to be spontaneous.

Review Questions

• How does the equation δg = δh - tδs relate to the concept of spontaneity in chemical reactions?
  • The equation δg = δh - tδs connects Gibbs free energy changes to reaction spontaneity. A negative value for δg indicates that a reaction can occur spontaneously under constant temperature and pressure. This means that either a decrease in enthalpy or an increase in entropy must drive the reaction forward. Understanding this relationship helps predict whether a given reaction will proceed without external intervention.
• In what situations might an endothermic reaction still be spontaneous according to the Gibbs free energy equation?
  • An endothermic reaction, which has a positive δh, can still be spontaneous if the increase in entropy (positive δs) is significant enough to outweigh the enthalpic cost when multiplied by temperature (t). For example, reactions like dissolving ammonium nitrate in water absorb heat but lead to an increase in disorder due to solvation. In such cases, even though δh is positive, if tδs is greater than δh, then δg will be negative, making the reaction spontaneous.
• Evaluate how changes in temperature affect the spontaneity of reactions as described by δg = δh - tδs.
  • Changes in temperature can significantly impact spontaneity as seen in the equation δg = δh - tδs. Increasing temperature can enhance the effect of entropy change (tδs), which may make reactions with positive entropy changes more favorable. For instance, some endothermic reactions may become spontaneous at higher temperatures because their tδs term grows larger. Conversely, decreasing temperature could suppress spontaneity for reactions that rely on increased disorder, illustrating how temperature serves as a critical factor in determining whether a process occurs naturally.

Related terms

Gibbs Free Energy: A thermodynamic potential that measures the maximum reversible work obtainable from a closed system at constant temperature and pressure.

Enthalpy: A measure of the total heat content of a system, represented by the symbol 'H', which includes internal energy plus the product of pressure and volume.

Entropy: A measure of the disorder or randomness in a system, represented by the symbol 'S', which indicates how much energy in a system is unavailable to do work.