Homework #2 (Chapter 4, 5, 6)
Due date: 2015.06.08
1. The molar volume of a certain solid is 161.0 cm3 mol-1 at 1.00 atm and 350.75 K, its melting temperature.
The molar volume of the liquid at this temperature and pressure is 163.3 cm3 mol-1.At 100 atm, the melting
temperature changes to 351.26 K. Calculate the enthalpy and entropy of fusion of the solid
2. The vapor pressure of dichloromethane at 24.1 °C is 53.3 kPa and its enthalpy of vaporization is 28.7 KJ
mol-1 Estimate the temperature at which its vapour pressure is 70.0 kPa.
3. When benzene freezes at 5.5 °C, its density changes from 0.879 g cm-3 to 0.891 g cm-3.Its enthalpy of
fusion is 10.59 kJ mol-1.Estimate the freezing pint of benzene at 1000 atm.
4. Naphthalene,C10H8 melts at 80.2 °C. If the vapour pressure of the liquid is 1.3kPa at 85.8 °C and 5.3 kPa
at 119.3 °C, use the Clausius–Clapeyron equation to calculate (a) the enthalpy of vaporization (b) the
normal boiling point, and (c) the entropy of vaporization at the boiling point.
5. What proportions of hexane and heptane should be mixed (a) by mole fraction, (b) by mass in order
to achieve the greatest entropy of mixing? Assum that hexane and heptane form nearly ideal solutions.
6. The osmotic pressure of solutions of polystyrene in toluene were measured at 25oC and the pressure
was expressed in terms of the height of the solvent of density 1.004g cm-3. Calculate molecular weight of
polystyrene from measured osmotic pressure.
c / (g dm-3)
2.042
6.613
9.521
12.602
h / cm
0.592
1.91
2.75
3.6
7. Methylethyl ether, CH3CH2OCH3 (A) and diborane, B2H6 (B) form a compound (ratio of A:B=1:1) which
melts congruently at 133K. The system exhibits two eutectics, one at 25 mol per cent B and 123 K and a
second at 90 mol per cent B and 104 K. The melting points of pure A and B are 131 K and 110 K,
respectively. Sketch the phase diagram for this system. Assume negligible solid-solid solubility.
8. Establish the relation between K and Kc for the reaction H2CO(g) ⇌ CO(g) + H2(g).
9. Calculate the percentage change in Kx for the reaction H2CO(g) ⇌ CO(g) + H2(g) when the total pressure
is increased from 1.0 bar to 2.0 bar at constant temperature.
10. Devise cells in which the following are the reactions and calculate the standard cell potential in
each case:
(a) Zn(s) + CuSO4(aq)  ZnSO4(aq) + Cu(s)
(b) 2AgCl(s) + H2(g)  2HCl(aq) + 2Ag(s)
(c) 2H2(g) + O2(g)  2H2O(l)