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

Slide 2/21 e CHEM1002 [Part 2] A/Prof Adam Bridgeman (Series 1) Dr Feike Dijkstra (Series 2) Weeks 8 – 13 Office Hours: Monday 2-3, Friday 1-2 Room: 543a

Slide 3/12 e Lecture 6: Physical States and Phase Changes Blackman Section 7.3 Entropy Lecture 7: Entropy Blackman Section 8.4 Lecture 8: Crystal Structures Blackman Chapter 7, Section 7.4 (pages )

Slide 4/12 e H 2 O(s)  H 2 O(l)  H = kJ mol -1 The temperature of the surroundings is also important! Spontaneous Reactions? In which direction is this reaction spontaneous? At -10 °C:liquid  solid At 10 °C:solid  liquid (exothermic) (endothermic)

Slide 5/12 e T warm Thermal Equilibration T hot T cold  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 the change in entropy (S) is: Derivation of this equation in CHEM2402 ?

Slide 6/12 e Energy Spreading Out… 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

Slide 7/12 e NO NO 2 N2O4N2O4 Entropy and Molecular Complexity Entropy increases as molecule grows more complex. animations

Slide 8/12 e Amount of Entropy (S) In many cases, the relative entropy of two different systems can be understood intuitively. S(gas) >> S(solid) S(solid+liquid) < S(solution) S(gas+liquid) > S(solution) S(3 mol) > S(2 mol) S(C 2 H 6 ) > S (CH 4 ) Energy spreads further in gas Energy localised in solid Energy spreads further in gas Entropy  amount of substance More bonds to spread energy around

Slide 9/12 x Which Has Higher Entropy? Which has the higher entropy in each of the following pairs? (a) 1 mol of SO 2 (g) or (b) 1 mol of CO 2 (s) or 1 mol of CO 2 (g) (c) 3 mol of O 2 or 2 mol of O 3 (g) (d) 1 mol of KBr(s) or 1 mol of KBr(aq) (e) Seawater in midwinter (2 0 C) or in midsummer (23 0 C) more atoms gas > solid more molecules solution > solid higher T 1 mol of SO 3 (g)

Slide 10/12 e  fus S Entropy: Qualitative More disordered = higher S For given substance: Same substance: melting point T Entropy (S) boiling point Solid Liquid Gas  vap S (increasing vibrations) (increasing translations) (increasing speeds) S liquid > S solid S gas > > higher T → higher S

Slide 11/12 x Practice Examples 1. When one mole of ice melts to liquid at 0 °C, A. The entropy of the system decreases. B. The entropy of the system remains the same. C. The entropy of the system increases. D. The order of the system increases. E. None of the above 2. The entropy of a chemical system will usually increase when A. A molecule is broken down into two or more smaller fragments. B. A reaction occurs that results in an increase in the moles of gas. C. A solid changes to a liquid. D. A liquid changes into a gas. E. All of the above

Slide 12/12 e 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