Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

6. Thermodynamics and Kinetics

Entropy

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If a reaction is exothermic, shouldn’t that be enough to determine favorability? Actually, no!

Even if a reaction is highly exothermic, the level of order it requires may make it statistically improbable.

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Explaining what entropy is.

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Entropy (ΔS) is the tendency of a system to take its most probable form.

  • Negative values (-) indicate less probable = Unfavored
  • Positive values (+) indicate more probable = Favored

There are 3 common ways to make reactions more probable (increase ΔS)

  • They all become more likely as we add heat to the reaction (increase T)
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3 ways to increase entropy.

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1. Increasing the Number of Molecules

Reactions that create extra molecules are more probable since there are more ways to arrange them.

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2. Phase Transition

Transformation of solid to liquid or liquid to gas is more probable since the molecules will have a greater vibrational freedom.

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3. Increasing Molecular Freedom of Motion

Converting cyclic molecules to acyclic molecules are more probable since it increases freedom of rotation.

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