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Chemical Energetics

Chemical Energetics: Application of Gibbs Free Energy in Thermodynamics

July 17, 2019 By Sean Chua Leave a Comment

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:

  1. 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:

I hope you find the content easy for your understanding and if you have any questions, leave me a comment below. Feel free to share this blog post with your friends.

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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PS: Under related articles below, there are several blog post discussions and questions related to Chemical Energetics. You can also do a keyword search using the search box at the top right hand corner.

PPS: If you need help with your A-Level H2 Chemistry, do join us in our weekly A-Level H2 Chemistry Tuition Class. Consistency is key to mastery for H2 Chemistry.

Cyril Teo HCI U to A H2 Chemistry in 5 Months
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