Question detail
Which of the following statements is true regarding Gibbs free energy?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Thermodynamics (A-level only)
Question
- A. A positive ΔG indicates a spontaneous reaction.
- B. A negative ΔG indicates a non-spontaneous reaction.
- C. ΔG can be zero for a reaction at equilibrium.
- D. ΔG is always positive for exothermic reactions.
Answer
ΔG can be zero for a reaction at equilibrium.
Explanation
At equilibrium, the Gibbs free energy change (ΔG) is zero, indicating that the forward and reverse reactions occur at the same rate. This is a key concept in thermodynamics.
Common mistake
Misunderstanding Gibbs Free Energy
Students often confuse the signs of ΔH and ΔS when predicting reaction feasibility using ΔG = ΔH - TΔS.
To fix this, remember that ΔG must be negative for a reaction to be feasible. Clearly identify the signs of ΔH and ΔS before substituting into the formula. For example, if ΔH is positive and ΔS is positive, the temperature will influence the sign of ΔG. Substitute values correctly: ΔG = ΔH - TΔS, then calculate and conclude whether the reaction is feasible based on the sign of ΔG.
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