key term - δg_f°

Definition

The standard Gibbs free energy of formation, represented as δg_f°, is the change in Gibbs free energy when one mole of a compound is formed from its elements in their standard states at a specified temperature, usually 298 K. This term is essential for understanding the spontaneity of reactions, as it provides a criterion for predicting whether a reaction will occur spontaneously under standard conditions.

5 Must Know Facts For Your Next Test

1. The standard Gibbs free energy of formation for elements in their standard state is defined as zero, making it easier to calculate for compounds.
2. A negative value of δg_f° indicates that the formation of the compound is spontaneous under standard conditions.
3. Calculating the standard Gibbs free energy change for a reaction involves using the standard Gibbs free energies of formation for both reactants and products.
4. The equation relating Gibbs free energy to enthalpy and entropy is given by $$ ext{ΔG} = ext{ΔH} - T ext{ΔS}$$, where T is the temperature in Kelvin.
5. The values of δg_f° can be found in tables, allowing chemists to easily assess the thermodynamic favorability of chemical reactions.

Review Questions

• How does δg_f° relate to the concept of spontaneity in chemical reactions?
  • δg_f° provides crucial information regarding the spontaneity of chemical reactions. A negative value indicates that a reaction is spontaneous under standard conditions, meaning it can proceed without external input. Conversely, if δg_f° is positive, it suggests that the reaction is non-spontaneous. Thus, understanding δg_f° helps predict whether reactants will transform into products naturally.
• Discuss how you would use δg_f° values to calculate the Gibbs free energy change for a specific reaction.
  • To calculate the Gibbs free energy change for a specific reaction, you would gather the δg_f° values for all reactants and products involved. The formula used is $$ ext{ΔG} = ext{Σ} ext{(δg_f° of products)} - ext{Σ} ext{(δg_f° of reactants)}$$. By plugging these values into the equation, you can determine whether the overall reaction is spontaneous or non-spontaneous based on the sign of ΔG.
• Evaluate how temperature might affect the spontaneity of a reaction in relation to δg_f°.
  • Temperature plays a significant role in determining spontaneity through its effect on both enthalpy and entropy, which are components in the Gibbs free energy equation $$ ext{ΔG} = ext{ΔH} - T ext{ΔS}$$. At higher temperatures, if the entropy change (ΔS) is positive and dominates over enthalpy (ΔH), a reaction that might be non-spontaneous at lower temperatures could become spontaneous. Therefore, analyzing how δg_f° varies with temperature can give insights into changing reaction favorability as conditions are modified.

Related terms

Gibbs Free Energy:

A thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure.

Spontaneity: The tendency of a process to occur without being driven by an external force; a spontaneous process releases free energy and tends to move toward equilibrium.

Enthalpy Change (ΔH): The heat content change of a system at constant pressure, which can influence the Gibbs free energy and spontaneity of a reaction.