Chapter 11

What intermolecular force(s) must be overcome to perform the following? (a) melt ice (b) sublime solid \(\mathrm{I}_{2}\) (c) convert liquid \(\mathrm{NH}_{3}\) to \(\mathrm{NH}_{3}\) vapor

Intermolecular forces: What type of forces must be overcome between \(\mathrm{I}_{2}\) molecules when solid \(\mathrm{I}_{2}\) dissolves in methanol, \(\mathrm{CH}_{3} \mathrm{OH}\) ? What type of forces must be disrupted between \(\mathrm{CH}_{3} \mathrm{OH}\) molecules when \(\mathrm{I}_{2}\) dissolves? What type of forces exist between \(\mathrm{I}_{2}\) and \(\mathrm{CH}_{3} \mathrm{OH}\) molecules in solution?

What type of intermolecular forces must be overcome in converting each of the following from a liquid to a gas? (a) liquid \(\mathrm{O}_{2}\) (c) \(\mathrm{CH}_{3} \mathrm{I}\) (methyl iodide) (b) mercury (d) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (ethanol)

What type of intermolecular forces must be overcome in converting each of the following from a liquid to a gas? (a) \(\mathrm{CO}_{2}\) (c) \(\mathrm{CHCl}_{3}\) (b) \(\mathrm{NH}_{3}\) (d) \(\mathrm{CCl}_{4}\)

Considering intermolecular forces in the pure substance, which of these substances exists as a gas at \(25^{\circ} \mathrm{C}\) and \(1 \mathrm{atm} ?\) (a) Ne (c) \(\mathrm{CO}\) (b) \(\mathrm{CH}_{4}\) (d) \(\mathrm{CCl}_{4}\)

Considering intermolecular forces in the pure substance, which of these substances exists as a gas at \(25^{\circ} \mathrm{C}\) and \(1 \mathrm{atm} ?\) (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (butane) (b) \(\mathrm{CH}_{3} \mathrm{OH}\) (methanol) (c) \(\mathrm{Ar}\)

In each pair of ionic compounds, which is more likely to have the more negative enthalpy of hydration? Briefly explain your reasoning in each case. (a) LiCl or CsCl (b) \(\mathrm{NaNO}_{3}\) or \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}\) (c) RbCl or \(\mathrm{NiCl}_{2}\)

When salts of \(\mathrm{Mg}^{2+}, \mathrm{Na}^{+},\) and \(\mathrm{Cs}^{+}\) are placed in water, the ions are hydrated. Which of these three cations is most strongly hydrated? Which one is least strongly hydrated?

Ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH},\) has a vapor pressure of \(59 \mathrm{mm}\) Hg at \(25^{\circ} \mathrm{C} .\) What quantity of energy as heat is required to evaporate \(125 \mathrm{mL}\) of the alcohol at \(25^{\circ} \mathrm{C}\) ? The enthalpy of vaporization of the alcohol at \(25^{\circ} \mathrm{C}\) is \(42.32 \mathrm{kJ} / \mathrm{mol}\). The density of the liquid is \(0.7849 \mathrm{g} / \mathrm{mL}\).

The enthalpy of vaporization of liquid mercury is \(59.11 \mathrm{kJ} / \mathrm{mol} .\) What quantity of energy as heat is required to vaporize \(0.500 \mathrm{mL}\) of mercury at \(357^{\circ} \mathrm{C},\) its normal boiling point? The density of mercury is \(13.6 \mathrm{g} / \mathrm{mL}\).

Which member of each of the following pairs of compounds has the higher boiling point? (a) \(\mathrm{O}_{2}\) or \(\mathrm{N}_{2}\) (c) HF or HI (b) \(\mathrm{SO}_{2}\) or \(\mathrm{CO}_{2}\) (d) \(\operatorname{SiH}_{4}\) or \(\operatorname{GeH}_{4}\)

Place the following four compounds in order of increasing boiling point: (a) \(\mathrm{C}_{5} \mathrm{H}_{12}\) (c) \(\mathrm{C}_{2} \mathrm{H}_{6}\) (b) \(\mathrm{CCl}_{4}\) (d) Ne

You are comparing three different substances, \(A, B\) and \(\mathrm{C},\) all liquids and having similar molar masses. The vapor pressure at \(25^{\circ} \mathrm{C}\) for substance \(\mathrm{A}\) is less than the vapor pressure for \(B\) at this temperature. Substance C has the highest boiling point of the three substances. List the three substances \(A, B\), or C in order of the strength of intermolecular forces, from least to greatest.

Can carbon monoxide \(\left(T_{c}=132.9 \mathrm{K} ; P_{c}=34.5 \mathrm{atm}\right)\) be liquefied at or above room temperature? Explain briefly.

Methane \(\left(\mathrm{CH}_{4}\right)\) cannot be liquefied at room temperature, no matter how high the pressure. Propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),\) another simple hydrocarbon, has a critical pressure of 42 atm and a critical temperature of \(96.7^{\circ} \mathrm{C} .\) Can this compound be liquefied at room temperature?

What is surface tension? Give an example illustrating the phenomenon of surface tension. Explain why surface tension is the consequence of intermolecular forces.

What factors affect the viscosity of a substance? Which of the following substances, water \(\left(\mathrm{H}_{2} \mathrm{O}\right),\) ethanol \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right),\) ethylene glycol \(\left(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right),\) and glycerol \(\left(\mathrm{HOCH}_{2} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{OH}\right),\) is expected to have the highest viscosity? Should viscosity of a substance be affected by temperature? Explain your answers.

If a piece of filter paper (an absorbent paper used in laboratories) is suspended above a beaker of water and just touching the surface, water will slowly move up the paper. What is the name given to this phenomenon, and how is this behavior explained?

When water is placed in a buret it forms a concave meniscus at the surface. In contrast, mercury (in a manometer for example) forms a convex meniscus (Figure 11.17 ). Explain why this phenomenon occurs, and why the two liquids give different results. Predict the meniscus shape if the buret is filled with ethylene glycol (HOCH_CH_OH).

What types of intermolecular forces are important in the liquid phase of (a) \(\mathrm{C}_{2} \mathrm{H}_{6}\) and (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHOH} ?\)

Which of the following ionic compounds will have the most negative enthalpy of hydration? (a) \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\) (c) \(\mathrm{NaCl}\) (b) \(\mathrm{CoCl}_{2}\) (d) \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3}\)

Rank the following compounds in order of increasing molar enthalpy of vaporization: \(\mathrm{CH}_{3} \mathrm{OH}, \mathrm{C}_{2} \mathrm{H}_{6}\) HCl.

Rank the following molecules in order of increasing boiling point: \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}, \mathrm{CH}_{3} \mathrm{F}, \mathrm{CH}_{3} \mathrm{Cl}\).

Mercury and many of its compounds are dangerous poisons if breathed, swallowed, or even absorbed through the skin. The liquid metal has a vapor pressure of 0.00169 \(\mathrm{mm}\) Hg at \(24^{\circ} \mathrm{C}\). If the air in a small room is saturated with mercury vapor, how many atoms of mercury vapor occur per cubic meter?

If you place 1.0 L of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) in a small laboratory that is \(3.0 \mathrm{m}\) long, \(2.5 \mathrm{m}\) wide, and \(2.5 \mathrm{m}\) high, will all the alcohol evaporate? If some liquid remains, how much will there be? The vapor pressure of ethanol at \(25^{\circ} \mathrm{C}\) is \(59 \mathrm{mm} \mathrm{Hg}\) and the density of the liquid at this temperature is \(0.785 \mathrm{g} / \mathrm{cm}^{3}\).

Cooking oil floats on top of water. From this observation, what conclusions can you draw regarding the polarity or hydrogen-bonding ability of molecules found in cooking oil?

Liquid ethylene glycol, \(\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH},\) is one of the main ingredients in commercial antifreeze. Would you predict its viscosity to be greater or less than that of ethanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH} ?\)

Liquid methanol, \(\mathrm{CH}_{3} \mathrm{OH},\) is placed in a glass tube. Is the meniscus of the liquid concave or convex? Explain briefly.

Rationalize the observation that \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) 1-propanol, has a boiling point of \(97.2^{\circ} \mathrm{C}\) whereas a compound with the same empirical formula, methyl ethyl ether \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{3}\right),\) boils at \(7.4^{\circ} \mathrm{C}\).

During thunderstorms in the Midwest, very large hailstones can fall from the sky. (Some are the size of golf balls!) To preserve some of these stones, we put them in the freezer compartment of a frost-free refrigerator. Our friend, who is a chemistry student, tells us to use an older model that is not frost- free. Why?

At the Fred Hutchison Cancer Research Center in Seattle it was discovered that mice can be put into a state of suspended animation by applying a low dose of hydrogen sulfide, \(\mathrm{H}_{2} \mathrm{S}\). The breathing rate of the mice fell from 120 to 10 breaths per minute and their temperature fell to just \(2^{\circ} \mathrm{C}\) above ambient temperature. Six hours later the mice were revived and seemed to show no negative effects. (a) Hydrogen sulfide is a gas at room temperature and normal atmospheric pressure whereas water is a liquid with a low vapor pressure under the same conditions. Explain this observation. (b) The \(\mathrm{H}_{2} \mathrm{S}\) gas delivered to the mice had a concentration of \(80 \mathrm{ppm} .\) (A concentration of \(1 \mathrm{ppm}\) is 1 part per million, or one molecule in every 1 million molecules.) If you deliver 1.0 L of gas (a mixture of \(\mathrm{O}_{2}, \mathrm{N}_{2},\) and \(\mathrm{H}_{2} \mathrm{S}\) ) at a total pressure of \(725 \mathrm{mm}\) Hg at a temperature of \(22^{\circ} \mathrm{C}\) what is the partial pressure of the \(\mathrm{H}_{2} \mathrm{S}\) gas? (c) Hydrogen sulfide can be converted to sulfuric acid. If \(5.2 \mathrm{L}\) of \(\mathrm{H}_{2} \mathrm{S}\) gas at \(130 \mathrm{mm}\) Hg pressure and \(25^{\circ} \mathrm{C}\) is allowed to react with \(\mathrm{O}_{2}\) gas, how many liters of \(\mathrm{O}_{2}\) gas, also at \(130 \mathrm{mm}\) Hg pressure and \(25^{\circ} \mathrm{C},\) are required for complete reaction? Assume the following reaction occurs. $$\mathrm{H}_{2} \mathrm{S}(\mathrm{g})+2 \mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{H}_{2} \mathrm{SO}_{4}(\ell)$$

A fluorocarbon, \(\mathrm{CF}_{4},\) has a critical temperature of \(-45.7^{\circ} \mathrm{C}\) and a critical pressure of 37 atm. Are there any conditions under which this compound can be a liquid at room temperature? Explain briefly.

List four properties of liquids that are directly determined by intermolecular forces.

List the following ions in order of hydration energies: \(\mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{Mg}^{2+}, \mathrm{Ca}^{2+} .\) Explain how you determined this order.

An \(8.82-\mathrm{g}\) sample of \(\mathrm{Br}_{2}\) is placed in an evacuated 1.00 L flask and heated to \(58.8^{\circ} \mathrm{C},\) the normal boiling point of bromine. Describe the contents of the flask under these conditions.

A pressure cooker (a kitchen appliance) is a pot on which the top seals tightly, allowing pressure to build up inside. You put water in the pot and heat it to boiling. At the higher pressure, water boils at a higher temperature, and this allows food to cook at a faster rate. Most pressure cookers have a setting of 15 psi, which means that the pressure in the pot is 15 psi above atmospheric pressure (1 atm \(=14.70\) psi). Use the Clausius- Clapeyron equation to calculate the temperature at which water boils in the pressure cooker.

Water \((10.0 \mathrm{g})\) is placed in a thick-walled glass tube whose internal volume is \(50.0 \mathrm{cm}^{3} .\) Then all the air is removed, the tube is sealed, and then the tube and contents are heated to \(100^{\circ} \mathrm{C}\) (a) Describe the appearance of the system at \(100^{\circ} \mathrm{C}\) (b) What is the pressure inside the tube? (c) At this temperature, liquid water has a density of \(0.958 \mathrm{g} / \mathrm{cm}^{3} .\) Calculate the volume of liquid water in the tube. (d) Some of the water is in the vapor state. Determine the mass of water in the gaseous state.