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LESSON 2

LESSON 2. THERMODYNAMICS AND EQUILIBRIUM. Recall:. Spontaneous Reactions: A reaction that will proceed without any apparent external cause (eg: addition of catalyst). A favourable change or reaction is one that has a natural tendency to occur.

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LESSON 2

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  1. LESSON 2 THERMODYNAMICS AND EQUILIBRIUM

  2. Recall: Spontaneous Reactions: A reaction that will proceed without any apparent external cause (eg: addition of catalyst)

  3. A favourable change or reaction is one that has a natural tendency to occur. There are three factors to consider when determining if a chemical reaction will occur in a certain direction.

  4. 1) ΔH (Enthalpy Change) • Systems tend to move towards minimum potential energy • Spontaneous reactions are exothermic A + B  C + D + kinetic energy

  5. 2) T (temperature) • Spontaneous reactions favour higher temperature 3) ΔS (ENTROPY CHANGE) What is ENTROPY CHANGE?

  6. Group Activity • Groups of 4 • Activity 1 = cards • Activity 2 = test tube + food colour

  7. Work +(energy)

  8. ΔS (Entropy Change) • Entropy is the degree of randomness in a system • Systems move towards maximum entropy or randomness As the degree of atomic molecular disorder increases, the entropy of the system increases (ΔS>0).

  9. Therefore, entropy favours side of the reaction which produces more particles since this creates greater disorder. Example: states of matter (solid, liquid, gas) Reactions tend to move in the direction that produces the most gas molecules.

  10. ΔSuniverse > 0 for a spontaneous process • ΔSuniverse < 0 for a nonspontaneous process • ΔSuniverse = 0 for a process at equilibrium

  11. Sample Problem: State whether entropy of the reaction increases or decreases: NH3(g) + HCl (g)  NH4Cl(s) decreases

  12. HOW DO YOU KNOW IF A REACTION IS MOVING IN THE FORWARD DIRECTION, THE REVERSE DIRECTION, OR IF IT IS EXACTLY AT EQUILIBRIUM?

  13. GIBBS FREE ENERGY ΔG = ΔH - TΔS • Free energy or Gibbs free energy allows us to predict whether the forward or reverse reaction is favoured. • Reactions that favour the products are considered spontaneous reactions.

  14. ΔG = ΔH - TΔS • If ΔG < 0 (  ) The forward reaction is spontaneous. • If ΔG > 0 ( + ) The forward reaction is not spontaneous. • If ΔG = 0 Equilibrium is reached.

  15. Reaction Spontaneity and the signs of ΔH, ΔS, and ΔG ΔH ΔS -TΔS ΔG Description - + - - spontaneous at all T + - + + nonspontaneous at all T + + - + or - spontan. at higher T nonspontan at lower T - - + + or - spontan. at lower T non spontan at higher T

  16. Sample Problems:

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