1. Slide 1/21 e 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. Slide 2/21 e 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. Slide 3/21 e Lecture 5: Periodic Trends Lecture 6: Physical States: Gases, Liquids and Solids Phase Changes Phase Diagrams Supercritical Fluids Blackman, Chapter 7, Sections 7.1 and 7.3 Physical States and Phase Diagrams

4. Slide 4/21 e Phase Changes: Δ pc H As heat is added to a solid, the molecules vibrate more and more, until.... The solid melts - an endothermic change as bonds are broken As heat is added to the liquid, the molecules move more and more, until.... The liquid boils - an endothermic change as bonds are broken As heat is added to the gas, the molecules move faster and faster

5. Slide 5/21 e Normal Melting and Boiling Points Vapour pressure: pressure exerted by vapour in equilibrium with its solid or liquid at stated temperature. Normal melting point: melting point when pressure equals 1 atm (101.3 kPa). Normal boiling point: temperature where vapour pressure of liquid equals 1 atm.

6. Slide 6/21 e Phase Diagrams Give temperatures and pressures where the different phases are stable. In a one-component system, there 3 phases (solid, liquid, gas):  3 two-phase equilibria liquid-gas, solid-liquid, solid-gas  1 three-phase equilibrium all three phases co-exist: triple point

7. Slide 7/21 e Plot vapour pressure of liquid as function of T (unique pressure where both phases exist at given T – co- existence curve of liquid and gas): liquid gas Temperature Pressure vapour pressure = external pressure Construction of a Phase Diagram I

8. Slide 8/21 e Plot melting point of solid as function of pressure (co-existence curve of liquid & solid): liquid solid Temperature Pressure Construction of a Phase Diagram II

9. Slide 9/21 e Construction of a Phase Diagram III Plot vapour pressure between solid and gas (unique pressure where both phases exist at given T – co-existence curve of solid & gas): solid gas Temperature Pressure Putting these all together gives phases at different P, T

10. Slide 10/21 e Construction of a Phase Diagram

11. Slide 11/21 e At 298 K and 1 atm,  CO 2 is a gas  decreasing the temperature, leads to deposition to solid:  increasing the pressure leads to condensation to liquid Phase Diagram for CO 2 liquid gas solid 298 K 1 atm sp = 195 K

12. Slide 12/21 e Phase Diagram for CO 2 On solid /liquid boundary, increasing pressure leads to formation of more solid Solid is more dense than the liquid. liquid gas solid

13. Slide 13/21 e Phase Diagram for H 2 O liquid gas solid 1 atm Starting at 1 atm and warming from T < 273 K,  ice melts at 273.15 K (normal melting point)  water boils at 373.15 K (normal boiling point) 273.15 K 373.15 K

14. Slide 14/21 e Phase Diagram for H 2 O Triple point: three phases co-exist only at single P,T : the Kelvin scale defined is by 273.16 K = temperature at which water is at triple point Note: T triple point is slightly higher than T normal melting liquid gas solid

15. Slide 15/21 e The Unusual Properties of Water The solid-liquid slope for H 2 O is negative:  ice melts if the pressure is increased at fixed temperature

16. Slide 16/21 e Critical Temperature and Pressure T & P at which boundary between liquid and vapour disappears. If sealed tube of CO 2 liquid and vapour heated, liquid-vapour phase boundary disappears at 31 °C and 73 atm: T > 31 °C no phase boundary: cannot say that it is either liquid or vapour vapour liquid supercritial fluid

17. Slide 17/21 e Supercritical Fluids  Supercritical fluids: substance above critical temperature (T c ).  Can behave as solvents dissolving a wide range of substances.  New industrial reaction medium.  Used in dry-cleaning and food production (e.g. caffeine extraction).

18. Slide 18/21 x 1. Which of the following statements concerning the phase diagram below is/are correct? (i). Moving from point A to B results in a phase transition from solid to liquid. (ii).Point D lies at the critical point. (iii).At point C, liquid and gas phases coexist in equilibrium. A. (i) only B. (ii) only C. (iii) only D. (i) and (ii) E. (i) and (iii) Practice Examples Temperature Pressure A B C D

19. Slide 19/21 x 2. The gas methane, CH 4, has a critical point at –82 °C and 46 atm. Can methane be liquefied at 25 °C? Explain your answer. (2008-J-3) Practice Examples 3. Which of the following gases can be liquefied at 25 °C? Gas Critical point CH 3 Cl144 °C, 66 atm SO 2 158 °C, 78 atm CH 4 –82 °C, 46 atm (A) SO 2 only (B) CH 4 only (C) CH 3 Cl and SO 2 (D) all of them (E) none of them

20. Slide 20/21 x Practice Examples 4. You may recall from a lecture demonstration or your laboratory work that solid CO 2 sublimes under ambient conditions while ice melts. Define the terms sublimation and melting. 5. What is a triple point (e.g. in the phase diagram of CO 2 or H 2 O)? 6. What does the different behaviour of ice and solid CO 2 indicate about the relative positions of their respective triple points? 2007-N-6

21. Slide 21/21 e Summary: Phase Diagrams Learning Outcomes - you should now be able to: Complete the worksheet Identify and explain the types of intermolecular and intramolecular forces Define and give two examples of allotropes Answer Review Problems 6.28-6.32 and 7.5-7.7 in Blackman Next lecture: 2 component phase diagrams and entropy