The standard free energy change (ΔG°) measures which of the following?

• A. Spontaneity of a chemical reaction under any condition
• B. Spontaneity of a chemical reaction under standard conditions
• C. Ratio of products to reactants
• D. Disorder in the universe

Answer: (B)

Verified step by step guidance

1. Understand that the standard free energy change (ΔG°) is a thermodynamic quantity that provides information about the spontaneity of a reaction under standard conditions, which typically means 1 M concentration for all reactants and products, 1 atm pressure, and a specified temperature, usually 25°C (298 K).
2. Recognize that ΔG° is related to the equilibrium constant (K) of a reaction. A negative ΔG° indicates that the reaction is spontaneous under standard conditions, meaning it will proceed in the forward direction to reach equilibrium.
3. Recall that ΔG° is calculated using the equation ΔG° = -RT ln(K), where R is the universal gas constant and T is the temperature in Kelvin. This equation shows the relationship between ΔG° and the ratio of products to reactants at equilibrium.
4. Differentiate between ΔG° and ΔG. While ΔG° refers to standard conditions, ΔG can vary depending on the actual concentrations of reactants and products, and it determines spontaneity under non-standard conditions.
5. Conclude that ΔG° does not measure the disorder in the universe directly; instead, it is related to the Gibbs free energy change, which considers both enthalpy and entropy changes in a system to determine spontaneity.