Chapter 11

The critical temperatures $(\mathrm{K})$ and pressures $(\mathrm{atm})$ of a series of halogenated methanes are as follows: $$\begin{array}{lcccc}\text{ Compound }& {\mathbf{C}\mathbf{C}\mathbf{l}}_3\mathbf{F}& {\mathbf{C}\mathbf{C}\mathbf{l}}_2{\mathbf{F}}_2& {\mathbf{C}\mathbf{C}\mathbf{I}\mathbf{F}}_3& {\mathbf{C}\mathbf{F}}_4\\ \text{ Critical temperature }& 471& 385& 302& 227\\ \text{ Critical pressure }& 43.5& 40.6& 38.2& 37.0\end{array}$$ (a) List the intermolecular forces that occur for each compound. (b) Predict the order of increasing intermolecular attraction, from least to most, for this series of compounds. (c) Predict the critical temperature and pressure for ${\mathrm{CCl}}_4$ based on the trends in this table. Look up the experimentally determined critical temperatures and pressures for ${\mathrm{CCl}}_4$, using a source such as the CRC Handbook of Chemistry and Physics, and suggest a reason for any discrepancies.

Explain how each of the following affects the vapor pressure of a liquid: (a) volume of the liquid, (b) surface area, (c) intermolecular attractive forces, (d) temperature, (e) density of the liquid.

(a) Place the following substances in order of increasing volatility: ${\mathrm{CH}}_4,{\mathrm{CBr}}_4,{\mathrm{CH}}_2{\mathrm{Cl}}_2,{\mathrm{CH}}_3\mathrm{Cl},{\mathrm{CHBr}}_3,$ and ${\mathrm{CH}}_2{\mathrm{Br}}_2.$ Explain. (b) How do the boiling points vary through this series?

True or false: (a) ${\mathrm{CBr}}_4$ is more volatile than ${\mathrm{CCl}}_4$. (b) ${\mathrm{CBr}}_4$ has a higher boiling point than ${\mathrm{CCl}}_4$. (c) ${\mathrm{CBr}}_4$ has weaker intermolecular forces than ${\mathrm{CCl}}_4$. (d) ${\mathrm{CBr}}_4$ has a higher vapor pressure at the same temperature than ${\mathrm{CCl}}_4$

(a) Two pans of water are on different burners of a stove. One pan of water is boiling vigorously, while the other is boiling gently. What can be said about the temperature of the water in the two pans? (b) A large container of water and a small one are at the same temperature. What can be said about the relative vapor pressures of the water in the containers?

Explain the following observations: (a) Water evaporates more quickly on a hot, dry day than on a hot, humid day. (b) It takes longer to cook an egg in boiling water at high altitudes than it does at lower altitudes.

Appendix B lists the vapor pressure of water at various external pressures. (a) Plot the data in Appendix B, vapor pressure (torr) versus temperature $\left({}^{\circ }\mathrm{C}\right).$ From your plot, estimate the vapor pressure of water at body temperature, ${37}^{\circ }\mathrm{C}$. (b) Explain the significance of the data point at 760.0 torr, ${100}^{\circ }\mathrm{C}$ (c) A city at an altitude of $5000\mathrm{ft}$ above sea level has a barometric pressure of 633 torr. To what temperature would you have to heat water to boil it in this city? (d) A city at an altitude of $500\mathrm{ft}$ below sea level would have a barometric pressure of 774 torr. To what temperature would you have to heat water to boil it in this city? (e) For the two cities in parts $(\mathrm{c})$ and $(\mathrm{d}),$ compare the average kinetic energies of the water molecules at their boiling points. Are the kinetic energies the same or different? Explain.

(a) What is the significance of the critical point in a phase diagram? (b) Why does the line that separates the gas and liquid phases end at the critical point?

(a) What is the significance of the triple point in a phase dia gram? (b) Could you measure the triple point of water b measuring the temperature in a vessel in which water vapo liquid water, and ice are in equilibrium under one atmospher of air? Explain.

Referring to Figure 11.28 , describe all the phase changes that would occur in each of the following cases: (a) Water vapor originally at 0.005 atm and $-{0.5}^{\circ }\mathrm{C}$ is slowly compressed at constant temperature until the final pressure is 20 atm. (b) Water originally at ${100.0}^{\circ }\mathrm{C}$ and $0.50\mathrm{atm}$ is cooled at constant pressure until the temperature is $-{10}^{\circ }\mathrm{C}$.