Chapter 9

Methyl alcohol can be used as a fuel instead of, or combined with, gasoline. A sample of methyl alcohol, \(\mathrm{CH}_{3} \mathrm{OH}\), in a flask of constant volume exerts a pressure of \(254 \mathrm{~mm} \mathrm{Hg}\) at \(57^{\circ} \mathrm{C}\). The flask is slowly cooled. (a) Assuming no condensation, use the ideal gas law to calculate the pressure of the vapor at \(35^{\circ} \mathrm{C}\); at \(45^{\circ} \mathrm{C}\). (b) Compare your answers in (a) with the equilibrium vapor pressures of methyl alcohol: \(203 \mathrm{~mm} \mathrm{Hg}\) at \(35^{\circ} \mathrm{C} ; 325 \mathrm{~mm} \mathrm{Hg}\) at \(45^{\circ} \mathrm{C}\). (c) On the basis of your answers to (a) and (b), predict the pressure exerted by the methyl alcohol in the flask at \(35^{\circ} \mathrm{C} ;\) at \(45^{\circ} \mathrm{C}\). (d) What physical states of methyl alcohol are present in the flask at \(35^{\circ} \mathrm{C} ?\) At \(45^{\circ} \mathrm{C} ?\)

Benzene, a known carcinogen, was once widely used as a solvent. \(\mathrm{A}\) sample of benzene vapor in a flask of constant volume exerts a pressure of \(325 \mathrm{~mm} \mathrm{Hg}\) at \(80^{\circ} \mathrm{C}\). The flask is slowly cooled. (a) Assuming no condensation, use the ideal gas law to calculate the pressure of the vapor at \(50^{\circ} \mathrm{C} ;\) at \(60^{\circ} \mathrm{C}\). (b) Compare your answers in (a) to the equilibrium vapor pressures of benzene: \(269 \mathrm{~mm} \mathrm{Hg}\) at \(50^{\circ} \mathrm{C}, 389 \mathrm{~mm} \mathrm{Hg}\) at \(60^{\circ} \mathrm{C}\). (c) On the basis of your answers to (a) and (b), predict the pressure exerted by the benzene at \(50^{\circ} \mathrm{C} ;\) at \(60^{\circ} \mathrm{C}\).

Naphthalene, \(\mathrm{C}_{10} \mathrm{H}_{8}\), is the substance present in some moth balls. Its vapor pressure at \(25^{\circ} \mathrm{C}\) is \(0.300 \mathrm{~mm} \mathrm{Hg}\). (a) How many milligrams of naphthalene will sublime into an evacuated 1.000-L flask? (b) If \(0.700 \mathrm{mg}\) of naphthalene is used, what will the final pressure be? What physical state(s) of naphthalene is (are) in the flask? (c) If \(4.00 \mathrm{mg}\) of naphthalene is used, what will the final pressure be? What physical state(s) of naphthalene is (are) in the flask?

The vapor pressure of \(\mathrm{I}_{2}(s)\) at \(30^{\circ} \mathrm{C}\) is \(0.466 \mathrm{~mm} \mathrm{Hg}\). (a) How many milligrams of iodine will sublime into an evacuated 1.00-L flask? (b) If \(2.0 \mathrm{mg}\) of \(\mathrm{I}_{2}\) is used, what will the final pressure be? (c) If \(10.0 \mathrm{mg}\) of \(\mathrm{I}_{2}\) is used, what will the final pressure be?

The vapor pressure of bromine, \(\mathrm{Br}_{2}(l)\) at \(25^{\circ} \mathrm{C}\) is \(228 \mathrm{~mm} \mathrm{Hg}\). (a) How many grams of bromine will be present as a gas if liquid bromine is poured into an evacuated 2.00-L flask at \(25^{\circ} \mathrm{C} ?\) (b) If \(2.00 \mathrm{~g}\) of bromine is used, what is the final pressure in the flask? Will there be liquid in the flask? (c) If \(2.00 \mathrm{~g}\) of bromine is put into an evacuated \(750.0\) -mL flask at \(25^{\circ} \mathrm{C}\), what is the final pressure in the flask? Will there be any liquid in the flask?

\(p\) -Dichlorobenzene, \(\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{Cl}_{2}\), can be one of the ingredients in mothballs. Its vapor pressure at \(20^{\circ} \mathrm{C}\) is \(0.40 \mathrm{~mm} \mathrm{Hg}\). (a) How many milligrams of \(\mathrm{C}_{6} \mathrm{H}_{4} \mathrm{Cl}_{2}\) will sublime into an evacuated 750-mL flask at \(20^{\circ} \mathrm{C}\) ? (b) If \(5.0 \mathrm{mg}\) of \(p\) -dichlorobenzene were put into an evacuated 750 -mL flask, how many milligrams would remain in the solid phase? (c) What is the final pressure in an evacuated 500 -mL flask at \(20^{\circ} \mathrm{C}\) that contains \(2.00 \mathrm{mg}\) of \(p\) -dichlorobenzene? Will there be any solid in the flask?

Chloroform, \(\mathrm{CHCl}_{3}\), was once used as an anesthetic. In spy movies it is the liquid put in handkerchiefs to render victims unconscious. Its vapor pressure is \(197 \mathrm{~mm} \mathrm{Hg}\) at \(23^{\circ} \mathrm{C}\) and \(448 \mathrm{~mm} \mathrm{Hg}\) at \(45^{\circ} \mathrm{C}\). Estimate its (a) heat of vaporization. (b) normal boiling point.

Methyl alcohol, \(\mathrm{CH}_{3} \mathrm{OH}\), has a normal boiling point of \(64.7^{\circ} \mathrm{C}\) and has a vapor pressure of \(203 \mathrm{~mm} \mathrm{Hg}\) at \(35^{\circ} \mathrm{C}\). Estimate (a) its heat of vaporization \(\left(\Delta H_{\text {vap }}\right)\). (b) its vapor pressure at \(40.0^{\circ} \mathrm{C}\).

Mt. McKinley in Alaska has an altitude of \(20,320 \mathrm{ft} .\) Water \(\left(\Delta H_{\mathrm{vap}}=\right.\) \(40.7 \mathrm{~kJ} / \mathrm{mol}\) ) boils at \(77^{\circ} \mathrm{C}\) atop Mt. McKinley. What is the normal atmospheric pressure at the summit?

The data below give the vapor pressure of octane, a major component of gasoline. \(\begin{array}{lllcl}\text { vp }(\mathrm{mm} \mathrm{Hg}) & 10 & 40 & 100 & 400 \\ t\left({ }^{\circ} \mathrm{C}\right) & 19.2 & 45.1 & 65.7 & 104.0\end{array}\) Plot ln vp versus \(1 / T\). Use your graph to estimate the heat of vaporization of octane. \(\left(\ln P=A-\frac{\Delta H_{\mathrm{vap}}}{R}\left(\frac{1}{T}\right)\right.\), where \(A\) is the \(y\) -intercept and \(\Delta H_{\mathrm{vap}}\) is the slope.)

19\. Argon gas has its triple point at \(-189.3^{\circ} \mathrm{C}\) and \(516 \mathrm{~mm} \mathrm{Hg}\). It has a critical point at \(-122^{\circ} \mathrm{C}\) and \(48 \mathrm{~atm}\). The density of the solid is \(1.65 \mathrm{~g} / \mathrm{cm}^{3}\) whereas that of the liquid is \(1.40 \mathrm{~g} / \mathrm{cm}^{3}\). Sketch the phase diagram for argon and use it to fill in the blanks below with the words "boils" "melts" "sublimes," or "condenses." (a) Solid argon at \(500 \mathrm{~mm} \mathrm{Hg} \) when the temperature is increased. (b) Solid argon at 2 atm increased. (c) Argon gas at \(-150^{\circ} \mathrm{C}\) when the pressure is increased. (d) Argon gas at \(-165^{\circ} \mathrm{C} \) when the pressure is increased.

Iodine has a triple point at \(114^{\circ} \mathrm{C}, 90 \mathrm{~mm} \mathrm{Hg}\). Its critical temperature is \(535^{\circ} \mathrm{C}\). The density of the solid is \(4.93 \mathrm{~g} / \mathrm{cm}^{3}\), and that of the liquid is \(4.00 \mathrm{~g} / \mathrm{cm}^{3}\). Sketch the phase diagram for iodine and use it to fill in the blanks using either "liquid" or "solid." (a) Iodine vapor at \(80 \mathrm{~mm} \mathrm{Hg}\) condenses to the when cooled sufficiently. (b) Iodine vapor at \(125^{\circ} \mathrm{C}\) condenses to the pressure is applied. (c) Iodine vapor at \(700 \mathrm{~mm} \mathrm{Hg}\) condenses to the when cooled above the triple point temperature.

Given the following data about xenon, $$ \begin{aligned} &\text { normal boiling point }=-108^{\circ} \mathrm{C} \\ &\text { normal melting point }=-112^{\circ} \mathrm{C} \\ &\text { triple point }=-121^{\circ} \mathrm{C} \text { at } 281 \mathrm{~mm} \mathrm{Hg} \\ &\text { critical point }=16.6^{\circ} \mathrm{C} \text { at } 58 \mathrm{~atm} \end{aligned} $$ (a) Construct an approximate phase diagram for xenon. (b) Estimate the vapor pressure of xenon at \(-115^{\circ} \mathrm{C}\). (c) Is the density of solid Xe larger than that for liquid Xe?

A pure substance \(\mathrm{X}\) has the following properties: \(\mathrm{mp}=90^{\circ} \mathrm{C}\), increasing slightly as pressure increases; normal bp \(=120^{\circ} \mathrm{C}\); liquid vp \(=65 \mathrm{~mm} \mathrm{Hg}\) at \(100^{\circ} \mathrm{C}, 20 \mathrm{~mm} \mathrm{Hg}\) at the triple point. (a) Draw a phase diagram for X. (b) Label solid, liquid, and vapor regions of the diagram. (c) What changes occur if, at a constant pressure of \(100 \mathrm{~mm} \mathrm{Hg}\), the temperature is raised from \(100^{\circ} \mathrm{C}\) to \(150^{\circ} \mathrm{C}\) ?

Arrange the following in order of decreasing boiling point. (a) \(\mathrm{I}_{2}\) (b) \(\mathrm{F}_{2}\) (c) \(\mathrm{Cl}_{2}\) (d) \(\mathrm{Br}_{2}\)

Arrange the following in order of increasing boiling point. (a) Ar (b) He (c) Ne (d) Xe

Which of the following would you expect to show dispersion forces? Dipole forces? (a) \(\mathrm{GeBr}_{4}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{2}\) (c) \(\mathrm{HF}(g)\) (d) \(\mathrm{TeCl}_{2}\)

Which of the following would you expect to show dispersion forces? Dipole forces? (a) \(\mathrm{PH}_{3}\) (b) \(\mathrm{N}_{2}\) (c) \(\mathrm{CH}_{4}\) (d) \(\mathrm{H}_{2} \mathrm{O}\)

Which of the following would show hydrogen bonding? (a) \(\mathrm{CH}_{3} \mathrm{~F}\) (b) \(\mathrm{HO}-\mathrm{OH}\) (c) \(\mathrm{NH}_{3}\) (d) \(\mathrm{H}_{3} \mathrm{C}-\mathrm{O}-\mathrm{CH}_{3}\)

Explain in terms of forces between structural units why (a) HI has a higher boiling point than \(\mathrm{HBr}\). (b) \(\mathrm{GeH}_{4}\) has a higher boiling point than \(\mathrm{SiH}_{4}\). (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) has a higher melting point than \(\mathrm{C}_{3} \mathrm{H}_{8}\). (d) \(\mathrm{NaCl}\) has a higher boiling point than \(\mathrm{CH}_{3} \mathrm{OH}\).

Explain in terms of forces between structural units why (a) \(\mathrm{Br}_{2}\) has a lower melting point than \(\mathrm{NaBr}\). (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) has a higher boiling point than butane, \(\mathrm{C}_{4} \mathrm{H}_{10}\). (c) \(\mathrm{H}_{2} \mathrm{O}\) has a higher boiling point than \(\mathrm{H}_{2} \mathrm{Te}\). (d) Acetic acid \(\mathrm{CH}_{3}-\mathrm{C}-\mathrm{OH}\) has a lower boiling point

In which of the following processes is it necessary to break covalent bonds as opposed to simply overcoming intermolecular forces? (a) melting mothballs made of naphthalene (b) dissolving HBr gas in water to form hydrobromic acid (c) vaporizing ethyl alcohol, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\) (d) changing ozone, \(\mathrm{O}_{3}\), to oxygen gas, \(\mathrm{O}_{2}\)

In which of the following processes is it necessary to break covalent bonds as opposed to simply overcoming intermolecular forces? (a) subliming dry ice (b) vaporizing chloroform \(\left(\mathrm{CHCl}_{3}\right)\) (c) decomposing water into \(\mathrm{H}_{2}\) and \(\mathrm{O}_{2}\) (d) changing chlorine molecules into chlorine atoms

For each of the following pairs, choose the member with the lower boiling point. Explain your reason in each case. (a) \(\mathrm{NaCl}\) or \(\mathrm{PCl}_{3}\) (b) \(\mathrm{NH}_{3}\) or \(\mathrm{AsH}_{3}\) (c) \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}\) or \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OCH}_{3}\) (d) \(\mathrm{HI}(g)\) or \(\mathrm{HCl}(g)\)

What are the strongest attractive forces that must be overcome to (a) boil silicon hydride \(\mathrm{SiH}_{4} ?\) (b) vaporize calcium chloride? (c) dissolve \(\mathrm{Cl}_{2}\) in carbon tetrachloride, \(\mathrm{CCl}_{4} ?\) (d) melt iodine?

What are the strongest attractive forces that must be overcome to (a) boil silicon hydride \(\mathrm{SiH}_{4} ?\) (b) vaporize calcium chloride? (c) dissolve \(\mathrm{Cl}_{2}\) in carbon tetrachloride, \(\mathrm{CCl}_{4} ?\) (d) melt iodine?

What are the strongest attractive forces that must be overcome to (a) melt ice? (b) sublime bromine? (c) boil chloroform (CHCl \(_{3}\) )? (d) vaporize benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) ?

Classify each of the following solids as metallic, network covalent, ionic, or molecular. (a) It is insoluble in water, melts above \(500^{\circ} \mathrm{C}\), and does not conduct electricity either as a solid, dissolved in water, or molten. (b) It dissolves in water but does not conduct electricity as an aqueous solution, as a solid, or when molten. (c) It dissolves in water, melts above \(100^{\circ} \mathrm{C}\), and conducts electricity when present in an aqueous solution.

Classify each of the following solids as metallic, network covalent, ionic, or molecular. (a) It melts below \(100^{\circ} \mathrm{C}\) and is insoluble in water. (b) It conducts electricity only when melted. (c) It is insoluble in water and conducts electricity.

Of the four general types of solids, which one(s) (a) are generally low-boiling? (b) are ductile and malleable? (c) are generally soluble in nonpolar solvents?

Of the four general types of solids, which one(s) (a) are generally insoluble in water? (b) have very high melting points? (c) conduct electricity as solids?

Classify each of the following species as molecular, network covalent, ionic, or metallic. (a) Na (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (d) \(\mathrm{C}_{60}\) (e) \(\mathrm{HCl}(a q)\)

Classify each of the following species as molecular, network covalent, ionic, or metallic. (a) W (b) \(\mathrm{NO}_{2}\) (c) \(\mathrm{C}\) (diamond) (d) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{CO}_{3}\) (e) \(\mathrm{F}_{2}(g)\)

Describe the structural units in (a) NaI (b) \(\mathrm{N}_{2}\) (c) \(\mathrm{KO}_{2}\) (d) \(\mathrm{Au}\)

Describe the structural units in (a) C (graphite) (b) \(\mathrm{SiC}\) (c) \(\mathrm{FeCl}_{2}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{2}\)

Nickel has an atomic radius of \(0.162 \mathrm{~nm}\). The edge of its cubic unit cell is \(0.458 \mathrm{~nm}\). What is the geometry of the nickel unit cell?

Vanadium crystallizes with a body-centered cubic unit cell. The volume of the unit cell is \(0.0278 \mathrm{~nm}^{3}\). What is its atomic radius?

The density of liquid mercury at \(20^{\circ} \mathrm{C}\) is \(13.6 \mathrm{~g} / \mathrm{cm}^{3}\), its vapor pressure is \(1.2 \times 10^{-3} \mathrm{~mm} \mathrm{Hg}\). (a) What volume (in \(\mathrm{cm}^{3}\) ) is occupied by one mole of \(\mathrm{Hg}(l)\) at \(20^{\circ} \mathrm{C}\) ? (b) What volume (in \(\mathrm{cm}^{3}\) ) is occupied by one mole of \(\mathrm{Hg}(\mathrm{g})\) at \(20^{\circ} \mathrm{C}\) and the equilibrium vapor pressure? (c) The atomic radius of \(\mathrm{Hg}\) is \(0.155 \mathrm{~nm}\). Calculate the volume (in \(\mathrm{cm}^{3}\) ) of one mole of \(\mathrm{Hg}\) atoms \(\left(V=4 \pi r^{3} / 3\right)\). (d) From your answers to (a), (b), and (c), calculate the percentage of the total volume occupied by the atoms in \(\mathrm{Hg}(l)\) and \(\mathrm{Hg}(g)\) at \(20^{\circ} \mathrm{C}\) and \(1.2 \times 10^{-3} \mathrm{~mm} \mathrm{Hg}\)

Consider a sealed flask with a movable piston that contains \(5.25 \mathrm{~L}\) of \(\mathrm{O}_{2}\) saturated with water vapor at \(25^{\circ} \mathrm{C}\). The piston is depressed at constant temperature so that the gas is compressed to a volume of \(2.00 \mathrm{~L}\). (Use the table in Appendix 1 for the vapor pressure of water at various temperatures.) (a) What is the vapor pressure of water in the compressed gas mixture? (b) How many grams of water condense when the gas mixture is compressed?

Mercury is an extremely toxic substance. Inhalation of the vapor is just as dangerous as swallowing the liquid. How many milliliters of mercury will saturate a room that is \(15 \times 12 \times 8.0 \mathrm{ft}\) with mercury vapor at \(25^{\circ} \mathrm{C}\) ? The vapor pressure of \(\mathrm{Hg}\) at \(25^{\circ} \mathrm{C}\) is \(0.00163 \mathrm{~mm} \mathrm{Hg}\) and its density is \(13 \mathrm{~g} / \mathrm{mL}\).

An experiment is performed to determine the vapor pressure of formic acid. A 30.0-L volume of helium gas at \(20.0^{\circ} \mathrm{C}\) is passed through \(10.00 \mathrm{~g}\) of liquid formic acid \((\mathrm{HCOOH})\) at \(20.0^{\circ} \mathrm{C}\). After the experiment, \(7.50 \mathrm{~g}\) of liquid formic acid remains. Assume that the helium gas becomes saturated with formic acid vapor and the total gas volume and temperature remain constant. What is the vapor pressure of formic acid at \(20.0^{\circ} \mathrm{C} ?\)

The normal boiling point for methyl hydrazine \(\left(\mathrm{CH}_{3} \mathrm{~N}_{2} \mathrm{H}_{3}\right)\) is \(87^{\circ} \mathrm{C}\). It has a vapor pressure of \(37.0 \mathrm{~mm} \mathrm{Hg}\) at \(20^{\circ} \mathrm{C}\). What is the concentration (in \(\mathrm{g} / \mathrm{L}\) ) of methyl hydrazine if it saturates the air at \(25^{\circ} \mathrm{C}\) ?

Which of the following statements are true? (a) The critical temperature must be reached to change liquid to gas. (b) To melt a solid at constant pressure, the temperature must be above the triple point. (c) \(\mathrm{CHF}_{3}\) can be expected to have a higher boiling point than \(\mathrm{CHCl}_{3}\) because CHF \(_{3}\) has hydrogen bonding. (d) One metal crystallizes in a body-centered cubic cell and another in a face-centered cubic cell of the same volume. The two atomic radii are related by the factor \(\sqrt{1.5}\)

In the blanks provided, answer the questions below, using LT (for is less than), GT (for is greater than), \(\mathrm{EQ}\) (for is equal to), or MI (for more information required). (a) The boiling point of \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{OH}(\mathrm{MM}=60.0 \mathrm{~g} / \mathrm{mol})\) the boiling point of \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{C}=\mathrm{O}(\mathrm{MM}=58.0 \mathrm{~g} / \mathrm{mol})\). (b) The vapor pressure of \(\mathrm{X}\) is \(250 \mathrm{~mm} \mathrm{Hg}\) at \(57^{\circ} \mathrm{C}\). Given a sealed flask at \(57^{\circ} \mathrm{C}\) that contains only gas, the pressure in the flask \(245 \mathrm{~mm} \mathrm{Hg}\) (c) The melting-point curve for Y tilts to the right of a straight line. The density of \(\mathrm{Y}(l) \quad\) the density of \(\mathrm{Y}(s)\). (d) The normal boiling point of \(\mathrm{A}\) is \(85^{\circ} \mathrm{C}\), while the normal boiling point of \(\mathrm{B}\) is \(45^{\circ} \mathrm{C}\). The vapor pressure of \(\mathrm{A}\) at \(85^{\circ} \mathrm{C}\) pressure of \(\mathrm{B}\) at \(45^{\circ} \mathrm{C}\). (e) The triple point of \(A\) is \(25 \mathrm{~mm} \mathrm{Hg}\) and \(5^{\circ} \mathrm{C}\). The melting point of \(\mathrm{A}\) \(5^{\circ} \mathrm{C}\)

A liquid has a vapor pressure of \(159 \mathrm{~mm} \mathrm{Hg}\) at \(20^{\circ} \mathrm{C}\) and \(165 \mathrm{~mm} \mathrm{Hg}\) at \(30^{\circ} \mathrm{C}\). Different amounts of the liquid are added to three identical evacuated steel tanks kept at \(20^{\circ} \mathrm{C}\). The tanks are all fitted with pressure gauges. For each part, write \(\mathbf{L} / \mathbf{G}\) if both liquid and gas are present. G if only gas is present. I if the situation is impossible. (a) The pressure gauge in Flask I registers a pressure of \(256 \mathrm{~mm} \mathrm{Hg}\). (b) The pressure gauge in Flask II registers a pressure of \(135 \mathrm{~mm} \mathrm{Hg}\). (c) The pressure gauge in Flask III registers a pressure of \(165 \mathrm{~mm} \mathrm{Hg}\) at \(30^{\circ} \mathrm{C}\). The temperature is lowered to \(20^{\circ} \mathrm{C}\), and the gauge registers a pressure of \(159 \mathrm{~mm} \mathrm{Hg}\).

Criticize or comment on each of the following statements. (a) Vapor pressure remains constant regardless of volume. (b) The only forces that affect boiling point are dispersion forces. (c) The strength of the covalent bonds within a molecule has no effect on the melting point of the molecular substance. (d) A compound at its critical temperature is always a gas regardless of pressure.

Differentiate between (a) a covalent bond and a hydrogen bond. (b) normal boiling point and a boiling point. (c) the triple point and the critical point. (d) a phase diagram and a vapor pressure curve. (e) volume effect and temperature effect on vapor pressure.

Four shiny solids are labeled \(\mathrm{A}, \mathrm{B}, \mathrm{C}\), and \(\mathrm{D}\). Given the following information about the solids, deduce the identity of \(\mathrm{A}, \mathrm{B}, \mathrm{C}\), and \(\mathrm{D}\). (1) The solids are a graphite rod, a silver bar, a lump of "fool's gold" (iron sulfide), and iodine crystals. (2) \(\mathrm{B}, \mathrm{C}\), and \(\mathrm{D}\) are insoluble in water. \(\mathrm{A}\) is slightly soluble. (3) Only C can be hammered into a sheet. (4) \(\mathrm{C}\) and \(\mathrm{D}\) conduct electricity as solids; B conducts when melted; \(\mathrm{A}\) does not conduct as a solid, melted, or dissolved in water.

A flask with a volume of \(10.0\) L contains \(0.400 \mathrm{~g}\) of hydrogen gas and \(3.20 \mathrm{~g}\) of oxygen gas. The mixture is ignited and the reaction $$ 2 \mathrm{H}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O} $$ goes to completion. The mixture is cooled to \(27^{\circ} \mathrm{C}\). Assuming \(100 \%\) yield, (a) What physical state(s) of water is (are) present in the flask? (b) What is the final pressure in the flask? (c) What is the pressure in the flask if \(3.2 \mathrm{~g}\) of each gas is used?

It has been suggested that the pressure exerted on a skate blade is sufficient to melt the ice beneath it and form a thin film of water, which makes it easier for the blade to slide over the ice. Assume that a skater weighs \(120 \mathrm{lb}\) and the blade has an area of \(0.10 \mathrm{in}^{2} .\) Calculate the pressure exerted on the blade \(\left(1 \mathrm{~atm}=15 \mathrm{lb} / \mathrm{in}^{2}\right)\). From information in the text, calculate the decrease in melting point at this pressure. Comment on the plausibility of this explanation and suggest another mechanism by which the water film might be formed.