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Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry , 2007 (John Wiley)      ISBN: 9 78047081 0866 . CHEM1002 [Part 2]. Dr Michela Simone Weeks 8 – 13 Office Hours: Monday 3-5, Friday 4-5

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  1. Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille,Chemistry, 2007 (John Wiley)     ISBN: 9 78047081 0866

  2. CHEM1002 [Part 2] Dr Michela Simone Weeks 8 – 13 Office Hours: Monday 3-5, Friday 4-5 Room: 412A (or 416) Phone: 93512830 e-mail:michela.simone@sydney.edu.au

  3. Entropy • Lecture 6: • Physical States and Phase Changes • Blackman Section 7.3 • Lecture 7: • Entropy • Blackman Section 8.4 • Lecture 8: • Crystal Structures • Blackman Chapter 7, Section 7.4 (pages 259-265)

  4. Spontaneous Reactions? H2O(s)  H2O(l) DH = +6.02 kJ mol-1 • In which direction is this reaction spontaneous? At -10 °C: liquid  solid (exothermic) At 10 °C: solid  liquid (endothermic) • The temperature of the surroundings is also important!

  5. Twarm Twarm Thermal Equilibration  Tcold ? Thot • Clearly, energy (heat) will move from the hotter body to the cooler body. Overall energy is constant. ENTROPY may be thought of as this tendency for energy to spread out as far as possible. The appropriate definition of thechange in entropy (S) is: Derivation of this equation in CHEM2402

  6. Energy can be spread out in two main ways: the molecules and their energy can be spread out further, or the energy can be spread across more molecules Energy Spreading Out…

  7. N2O4 NO2 Entropy and Molecular Complexity animations NO • Entropy increases as molecule grows more complex.

  8. In many cases, the relative entropy of two different systems can be understood intuitively. Amount of Entropy (S) Energy spreads further in gas S(gas) >> S(solid) S(solid+liquid) < S(solution) S(gas+liquid) > S(solution) S(3 mol) > S(2 mol) S(C2H6) > S (CH4) Energy localised in solid Energy spreads further in gas Entropy  amount of substance More bonds to spread energy around

  9. Which Has Higher Entropy? • Which has the higher entropy in each of the following pairs? 1 mol of SO3(g) more atoms (a) 1 mol of SO2(g) or gas > solid (b) 1 mol of CO2(s) or 1 mol of CO2(g) more molecules (c) 3 mol of O2 or 2 mol of O3(g) (d) 1 mol of KBr(s) or 1 mol of KBr(aq) solution > solid (e) Seawater in midwinter (2 0C) or in midsummer (23 0C) higher T

  10. More disordered = higher S For given substance: Entropy: Qualitative Sliquid > Ssolid Sgas > > • Same substance: higher T → higher S Gas (increasing speeds) DvapS Entropy (S) Liquid (increasing translations) DfusS Solid (increasing vibrations) T melting point boiling point

  11. Practice Examples

  12. Summary: Entropy, • Learning Outcomes - you should now be able to: • Complete the worksheet • Explain what entropy is to a non-science friend • Predict whether entropy will increase or decrease in a chemical or physical process • Apply the entropy concept qualitatively to explain direction of phase change • Next lecture: • Crystal structures

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