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Chapter 19

Chapter 19. Entropy, Spontaneity and Free Energy. First Law of Thermodynamics. Law of Conservation of Energy . This law suggests that energy can be transferred from one system to another in many forms. However, it can not be created nor destroyed .

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Chapter 19

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  1. Chapter 19 Entropy, Spontaneity and Free Energy

  2. First Law of Thermodynamics • Law of Conservation of Energy. • This law suggests that energy can be transferred from one system to another in many forms. However, it can not be created nor destroyed. • Thus, the total amount of energy available in the Universe is constant.

  3. This is also evident in Enthalpy Rxns • Cdiamond + O2(g) CO2(g) ΔH = -396 kj • CO2(g)  Cdiamond+ O2(g) ΔH= +396 kj • What are the forms of Energy?

  4. First Law of Thermodynamics • The first law is all about the accounting of energy. • How much energy is involved in the change? • Does the energy flow in or out of a system? • What form does the energy finally assume?

  5. Spontaneous Processes • A process that will occur without any energy input from the surroundings. A process that will occur on its own. • Thermodynamics considers only the initial and final states of a reaction and not the pathway.

  6. Spontaneous does not mean fast!

  7. Spontaneous reactions: these reactions never occur in the reverse. • Heat moves from warm object to cold. • Wood burns in an exothermic reaction. • Below 0 ° water freezes; above 0 ° water melts.

  8. Spontaneous movement of gases

  9. Entropy

  10. Entropy symbol: S • The driving force for a spontaneous reaction is an increase in entropy in the universe. • Entropy is randomness, or the measure of molecular disorder.

  11. Entropy is the associated with probability • Nature proceeds spontaneously towards the states that have the highest probability of existing. • So… which arrangement is most likely to occur?

  12. Probability

  13. 1 2 3 4 5

  14. Probability • The probability is that in an arrangement of 4 molecules and two places that arrangement 3 is the most likely. • The likelihood of all 4 in one chamber is low.

  15. Probability of finding all gas molecules in left bulb as a function of the total number of gas particles • # molecules Probability • 1 ½ • 2 ½ x ½ = ¼ • 3 ½ x ½ x ½ = 1/(2)3 • 5 ½ x ½ x ½ x ½ x ½ = 1/(2)5 • n ½ x ½ x ½ x…1/(2)n

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