In the previous post, we have look into how Gibbs Free Energy change, ΔG is used to predict the spontaneity of a chemical reaction.
Today, we shall look into the application of this important concept and see how we can apply it to solve GCE A-Level H2 Chemistry exam-based questions. The following type of question is commonly tested in JC1 Promotional Examination (Promos) as well as JC2 Preliminary Examination (Prelims).
Question:
When 1 mole of carbon dioxide gas solidifies as dry ice, 25.2 kJ of heat energy is evolved. The sublimation temperature of carbon dioxide is -78.5 °C. What is the entropy change when 132 g of carbon dioxide gas solidifies at this temperature?
Thought Process:
- Recall that ΔG is:
- < 0 for any spontaneous reaction
- > 0 for any non-spontaneous reaction
- = 0 for any reaction in equilibrium
2. Recall the formula which links ΔG to ΔH, ΔS and T:
ΔG = ΔH – TΔS
3. Recall the units involved for the different thermodynamics terms:
- Units of ΔG and ΔH are kJmol-1 or Jmol-1.
- Units of ΔS are kJmol-1K-1 or Jmol-1K-1.
- Units of T is K.
Suggested Solution:
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Do stay tuned to the upcoming posts as we will be looking at some GCE A-Level H2 Chemistry examination questions.
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