Question detail
For a reaction with ΔH = -100 kJ and ΔS = 200 J/K, calculate ΔG at 400 K.
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. -120 kJ
- B. -80 kJ (A-level cue 34f80dea distractor 1)
- C. -100 kJ (A-level cue 34f80dea distractor 2)
- D. -140 kJ (A-level cue 34f80dea distractor 3)
Answer
-120 kJ
Explanation
The correct option is -120 kJ. -120 kJ is correct because it supports the objective: Use ΔG = ΔH - TΔS to calculate Gibbs free energy change.. The reasoning stays within Entropy and Gibbs free energy (A-level only) and avoids drifting into a similar A-Level Chemistry idea. This item is treated as conceptual revision rather than a formal calculation item because the validated answer is an explanation or option choice, not a worked numerical response.
Common mistake
Incorrect Use of Temperature Units
Students often forget to convert temperature from Celsius to Kelvin when using the Gibbs free energy equation ΔG = ΔH - TΔS.
Always convert the temperature to Kelvin by adding 273.15 to the Celsius value before substituting into the equation. For example, if the temperature is 25°C, convert it to Kelvin: T = 25 + 273.15 = 298.15 K. Then, use this value in the Gibbs free energy calculation.
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