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Entropy, Enthalpy and Spontaneous Reactions!

Entropy, Enthalpy and Spontaneous Reactions!. Entropy (S), Ethalpy (H) and Gibbs Free Energy (G). What do we know about chemical reactions?. We can write chemical reactions and show how atoms and molecules come together to form products.

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Entropy, Enthalpy and Spontaneous Reactions!

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  1. Entropy, Enthalpy and Spontaneous Reactions! Entropy (S), Ethalpy (H) and Gibbs Free Energy (G)

  2. What do we know about chemical reactions? • We can write chemical reactions and show how atoms and molecules come together to form products. • We can determine the energy change in a chemical reaction ΔH. • We can determine if a reaction is fast or slow (rate). • We can determine how to increase the rate of the reaction.

  3. How do we know if a reaction will occur or not? • Do the reaction in the lab! • Use thermodynamic qualities to determine spontaneity.

  4. What is spontaneous? • Going downhill happens without having to put any energy into it. • Spontaneous • Going uphill only occurs if you continually add energy to the process. • Non-spontaneous

  5. Enthalpy • Nature favours a decrease in potential energy. (NATURE IS LAZY!) • Exothermic reactions are favoured over endothemic reactions. • -ΔH means the reaction is favoured. • +ΔH means the reaction is not favoured.

  6. Entropy • Nature favours an increase in Entropy. (NATURE IS MESSY) • This is the systems state of disorder. • It is dependent on the temperature. • Entropy = S, Change in Entropy = ΔS, kJ/K

  7. Decrease in entropy  -ΔS, Unfavoured. Increase in entropy  • + ΔS, Favoured

  8. When does entropy increase or decrease?

  9. Are these reactions favoured in terms of entropy? • 2 K(s) + Cl2(l)  2KCl(s) • 2LiBr(s)  2Li(s) + Br2(l) • N2(g) + 3H2(g) 2NH3(g) • Unfavoured • Favoured • Unfavoured

  10. Spontaneous? • NaOH(s) Na+(aq) + OH-(aq) ΔH = -44.4 kJ • Enthalpy • Entropy • Spontaneity • -Δ H Favoured • +ΔS Favoured • This reaction will ALWAYS be spontaneous!

  11. Spontaneous?2Al(s) + 3O2(g)  2Al2O3(s) ΔH = -3351 J • Enthalpy • Entropy • Spontaneity? • -ΔH Strongly favoured. • -ΔS Not favoured. • Spontaneous at very low temperatures.

  12. Spontaneous?KNO3(s) K+(aq) + NO3-(aq) ΔH = +34 kJ • Enthalpy • Entropy • Spontaneous? • +ΔH unfavourable • +ΔS favourable • Spontaneous at very high temperatures!

  13. Spontaneous?6CO2(g) + 6H2O(g)  C6H12O6(s) + 6O2(g) ΔH = +2868 kJ/mol • Enthalpy • Entropy • Spontaneous? • +ΔH unfavoured • -ΔS unfavoured • This reaction is NEVER spontaneous and requires a constant input of energy!

  14. ΔG = ΔH-TΔS • ΔG < 0 the reaction is spontaneous. • ΔG> 0 the reaction is not spontaneous. • Gibbs Free energy is the amount of energy available to do work.

  15. Classwork • Complete handout and reading for tomorrow.

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