Chapter 8

Acetylene can be made by reacting calcium carbide with water. $$\mathrm{CaC}_{2}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{2}(\mathrm{~g})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})$$ Assume that you place \(2.65 \mathrm{~g} \mathrm{CaC}_{2}\) in excess water and collect the acetylene over water. The volume of the acetylene and water vapor is \(795 \mathrm{~mL}\) at \(25.0^{\circ} \mathrm{C}\) and a barometric pressure of \(735.2 \mathrm{mmHg}\). Calculate the percent yield of acetylene. The vapor pressure of water at \(25^{\circ} \mathrm{C}\) is \(23.8 \mathrm{mmHg}\).

You are given two flasks of equal volume. Flask A contains \(\mathrm{H}_{2}\) at \(0{ }^{\circ} \mathrm{C}\) and 1 atm pressure. Flask \(\mathrm{B}\) contains \(\mathrm{CO}_{2}\) gas at \(0{ }^{\circ} \mathrm{C}\) and 2 atm pressure. Compare these two samples with respect to each of these properties. (a) Average kinetic energy per molecule (b) Average molecular velocity (c) Number of molecules

Place these gases in order of increasing average molecular speed at \(25^{\circ} \mathrm{C}: \mathrm{Kr}, \mathrm{CH}_{4}, \mathrm{~N}_{2},\) and \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\).

Arrange these four gases in order of increasing average molecular speed at \(25^{\circ} \mathrm{C}: \mathrm{Cl}_{2}, \mathrm{~F}_{2}, \mathrm{~N}_{2},\) and \(\mathrm{O}_{2}\).

If equal amounts of the four inert gases \(\mathrm{Ar}, \mathrm{Ne}, \mathrm{Kr},\) and Xe are released at the same time at one end of a long, evacuated tube, which gas will reach the other end of the tube first? Explain your answer.

The reaction of \(\mathrm{SO}_{2}\) with \(\mathrm{Cl}_{2}\) to give dichlorine oxide is $$\mathrm{SO}_{2}(\mathrm{~g})+2 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{SOCl}_{2}(\mathrm{~g})+\mathrm{Cl}_{2} \mathrm{O}(\mathrm{g})$$ Place all molecules in the equation in order of increasing rate of effusion.

From the density of liquid water and its molar mass, calculate the volume that 1 mol liquid water occupies. If water were an ideal gas at STP, what volume would a mole of water vapor occupy? Can we achieve the STP conditions for water vapor? Why or why not?

At low temperatures and very low pressures, gases behave ideally, but as the pressure is increased the product \(P V\) becomes less than the product \(n R T\). Give a molecular-level explanation of this fact.

At high temperatures and low pressures, gases behave ideally, but as the pressure is increased the product \(P V\) becomes greater than the product \(n R T\). Give a molecularlevel explanation of this fact.

The densities of liquid noble gases and their normal boiling points are given in this table. $$ \begin{array}{lcc} \hline & \begin{array}{l} \text { Normal Boiling } \\ \text { Paint (K) } \end{array} & \begin{array}{c} \text { Liquid Density } \\ \left(g / \mathrm{cm}^{3}\right) \end{array} \\ \hline \mathrm{He} & 4.2 & 0.125 \\ \mathrm{Ne} & 27.1 & 1.20 \\ \mathrm{Ar} & 87.3 & 1.40 \\ \mathrm{Kr} & 120 . & 2.42 \\ \mathrm{Xe} & 165 & 2.95 \\ \hline \end{array} $$ Calculate the volume occupied by 1 mol of each of these liquids. Comment on any trend that you see. Determine the volume occupied by exactly \(1 \mathrm{~mol}\) of each of these substances as an ideal gas at STP. Which gas would you expect to show the largest deviations from ideality at room temperature? Why?

Explain the major roles played by nitrogen in the atmosphere. Do the same for oxygen.

Beginning at Earth's surface and proceeding upward, name the first two layers or regions of the atmosphere. Describe, in general, the kinds of chemical reactions that occur in each layer.

(a) Calculate the volume of air in liters that you would inhale in 24 hours assuming that you inhaled 16 breaths per minute and each breath had a volume of approximately \(0.50 \mathrm{~L} .\left(T=18.0^{\circ} \mathrm{C} ; P=0.970 \mathrm{~atm} .\right)\) (b) Compare that total volume to the volume of air in a typical residence hall room, approximately \(864 \mathrm{ft}^{3}\) (approx. \(\left.28 \mathrm{~L} / \mathrm{ft}^{3}\right)\) (c) Calculate the number of oxygen molecules you inhaled during that time.

At a spot 3,000 feet above sea level you take a sip of water through a straw before you begin a mountain hike. You take another sip when you reach the top at \(10,400 \mathrm{ft}\). At which elevation is it easier to sip the water? Explain.

Felix Baumgartner, wearing a special pressurized suit, set a new skydiving record on October 14,2012 by free falling from an altitude of \(39 \mathrm{~km}\), near the top of the stratosphere. Baumgartner was in a state of weightlessness for the first \(25 \mathrm{~s}\) of his free fall. Explain why he was able to gain maneuverability and ultimately deploy his parachute only after reaching the troposphere.

Can ozone form in the stratosphere at night? Explain why or why not.

The molecule \(\mathrm{CH}_{3} \mathrm{~F}\) has much less ozone-depletion potential than the corresponding molecule \(\mathrm{CH}_{3} \mathrm{Cl}\). Explain why.

Can CFCs catalyze the destruction of ozone in the stratosphere at night? Explain.

Are CFCs toxic? Compare the toxicity of CFCs with that of compounds used for refrigeration before CFCs were invented. Look up the toxicity of these compounds on the Internet.

What is the difference between the greenhouse effect and global warming? How are they related?

Name four greenhouse gases, and explain why they are called that.

Carbon dioxide is known to be a major contributor to the greenhouse effect. List some of its sources in our atmosphere and some of the processes that remove it. Currently, which predominates - the production of \(\mathrm{CO}_{2}\) or its removal?

Name a favorable effect of the global increase of \(\mathrm{CO}_{2}\) in the atmosphere.

Define air pollution in terms of the kinds of pollutants, their sources, and the ways they are harmful.

Assume that limestone, \(\mathrm{CaCO}_{3}\), is used to remove \(90 . \%\) of the sulfur from 4.0 metric tons of coal containing \(2.0 \% \mathrm{~S} .\) The product is \(\mathrm{CaSO}_{4}\) $$\mathrm{CaCO}_{3}(\mathrm{~s})+\mathrm{SO}_{3}(\mathrm{~g}) \longrightarrow \mathrm{CaSO}_{4}(\mathrm{~s})+\mathrm{CO}_{2}(\mathrm{~g})$$ Calculate the mass of limestone required. Express your answer in metric tons.

Approximately 65 million metric tons of \(\mathrm{SO}_{2}\) enter the atmosphere every year from the burning of coal. If coal, on average, contains \(2.0 \% \mathrm{~S},\) calculate how many metric tons of coal were burned to produce this much \(\mathrm{SO}_{2}\). A 1000-MW power plant burns about 700 . metric tons of coal per hour. Calculate the number of hours the quantity of coal will burn in one of these power plants.

Calculate the mass of gasoline that must be burned according to the reaction $$\mathrm{C}_{8} \mathrm{H}_{18}(\ell)+8.5 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 8 \mathrm{CO}(\mathrm{g})+9 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$$ to raise the CO concentration to 1000 . ppm in a garage that measures \(7.00 \mathrm{~m} \times 3.00 \mathrm{~m} \times 3.00 \mathrm{~m}\). (Assume STP conditions.)

What atmospheric reaction produces nitrogen monoxide, NO?

Give an example of a situation where atmospheric ozone is beneficial and an example of a situation where it is harmful. Explain how ozone is beneficial and how it is harmful.

\(\mathrm{HCl}\) can be made by the direct reaction of \(\mathrm{H}_{2}\) and \(\mathrm{Cl}_{2}\) in the presence of light. Assume that \(3.0 \mathrm{~g} \mathrm{H}_{2}\) and \(140 . \mathrm{g}\) \(\mathrm{Cl}_{2}\) are mixed in a \(10-\mathrm{L}\) flask at \(28{ }^{\circ} \mathrm{C}\), and the flask is sealed. Before the reaction: (a) Calculate the partial pressures of the two reactants. (b) Calculate the total pressure in the flask. After the reaction: (c) Calculate the total pressure in the flask. (d) What reactant remains in the flask? Calculate the amount (mol) that remains. (e) Calculate the partial pressure of each gas. (f) Calculate the pressure inside the flask if the temperature is increased to \(40 .{ }^{\circ} \mathrm{C}\).

Calculate the densities of \(\mathrm{Cl}_{2}\) and of \(\mathrm{SO}_{2}\) at \(25^{\circ} \mathrm{C}\) and \(0.750 \mathrm{~atm} .\) Then, calculate the density of \(\mathrm{Cl}_{2}\) at \(35^{\circ} \mathrm{C}\) and \(0.750 \mathrm{~atm}\) and the density of \(\mathrm{SO}_{2}\) at \(25^{\circ} \mathrm{C}\) and \(2.60 \mathrm{~atm} .\)

The gas burner in a stove or furnace admits enough air so that methane gas can react completely with oxygen in the air according to the equation $$\mathrm{CH}_{4}(\mathrm{~g})+2 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \mathrm{CO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$$ Air is one-fifth oxygen by volume. Both air and methane gas are supplied to the flame by passing them through separate small tubes. Compared with the tube for the methane gas, determine how much bigger the cross section of the tube for the air needs to be. Assume that both gases are at the same \(T\) and \(P\).

You have 100 balloons of equal volume filled with a total of \(26.8 \mathrm{~g}\) helium gas at \(23.0^{\circ} \mathrm{C}\) and \(748 \mathrm{mmHg}\). The total volume of these balloons is \(168 \mathrm{~L}\). You are given 150 more balloons of the same size and \(41.8 \mathrm{~g}\) He gas. The temperature and pressure remain the same. Determine by calculation whether you will be able to fill all the balloons with the He you have available.

At \(25^{\circ} \mathrm{C}\), the measured pressure of acetic acid vapor, \(\mathrm{CH}_{3} \mathrm{COOH}(\mathrm{g})\), is significantly lower than that predicted by the ideal gas law. Explain this difference.

The air in a flask is evacuated by a high-quality vacuum system. The vacuum created corresponds to \(1.0 \times 10^{-8}\) Torr at \(25^{\circ} \mathrm{C}\). Calculate the number of molecules of air per \(\mathrm{cm}^{3}\) remaining in the apparatus at this temperature and pressure.

Consider a sample of \(\mathrm{N}_{2}\) gas under conditions in which it obeys the ideal gas law exactly. Which of these statements is/are true? (a) A sample of \(\mathrm{Ne}(\mathrm{g})\) under the same conditions must obey the ideal gas law exactly. (b) The speed at which one particular \(\mathrm{N}_{2}\) molecule is moving changes from time to time. (c) Some \(\mathrm{N}_{2}\) molecules are moving more slowly than some of the molecules in a sample of \(\mathrm{O}_{2}(\mathrm{~g})\) under the same conditions. (d) Some \(\mathrm{N}_{2}\) molecules are moving more slowly than some of the molecules in a sample of \(\mathrm{Ne}(\mathrm{g})\) under the same conditions. (e) When two \(\mathrm{N}_{2}\) molecules collide, it is possible that both may be moving faster after the collision than they were before.

In this chapter Boyle's, Charles's, and Avogadro's laws were presented as word statements and mathematical relationships. Express each of these laws graphically.

A substance is analyzed and found to contain \(85.7 \%\) carbon and \(14.3 \%\) hydrogen by mass. A gaseous sample of the substance is found to have a density of \(1.87 \mathrm{~g} / \mathrm{L}\) at STP. (a) Calculate the molar mass of the compound. (b) Determine the empirical and molecular formulas of the compound. (c) Draw two possible Lewis structures for molecules of the compound.

A compound consists of \(37.5 \% \mathrm{C}, 3.15 \% \mathrm{H},\) and \(59.3 \%\) \(\mathrm{F}\) by mass. When \(0.298 \mathrm{~g}\) of the compound is heated to 50\. \({ }^{\circ} \mathrm{C}\) in an evacuated \(125-\mathrm{mL}\) flask, the pressure is observed to be \(750 . \mathrm{mmHg}\). The compound has three isomers. (a) Calculate the molar mass of the compound. (b) Determine the empirical and molecular formulas of the compound. (c) Draw the Lewis structure for each isomer of the compound.

One very cold winter day you and a friend purchase a helium-filled balloon. As you leave the store and walk down the street, your friend notices the balloon is not as full as it was a moment ago in the store. He says the balloon is defective and he is taking it back. Do you agree with him? Explain why you do or do not agree.

A \(2.69-\mathrm{g} \mathrm{PCl}_{5}\) sample was completely vaporized in a 1.00-L flask at \(250 .{ }^{\circ} \mathrm{C}\). The resulting pressure in the flask was 1.00 atm. At this temperature, there is the possibility that some \(\mathrm{PCl}_{5}(\mathrm{~g})\) decomposed to \(\mathrm{PCl}_{3}(\mathrm{~g})\) and \(\mathrm{Cl}_{2}(\mathrm{~g}) .\) (a) Show calculations to determine whether any of the \(\mathrm{PCl}_{5}(\mathrm{~g})\) decomposed. (b) If some of the \(\mathrm{PCl}_{5}(\mathrm{~g})\) decomposed, calculate the partial pressures of each of the three gaseous species under these experimental conditions.

The relation between the average kinetic energy of a molecule, \(\frac{1}{2} m v^{2},\) and the absolute temperature is $$\frac{1}{2} m v^{2}=\frac{3}{2} k T$$ \(m\) is the mass of the molecule; \(v\) is its average velocity; \(k\) is \(1.38 \times 10^{-23} \mathrm{~J} / \mathrm{K} ; T\) is the absolute temperature. \(1 \mathrm{~J}=1 \mathrm{~kg} \mathrm{~m}^{2} \mathrm{~s}^{-2}\). Calculate the average velocity of a nitrogen dioxide molecule in the atmosphere at \(27.0^{\circ} \mathrm{C}\).

The reaction between the gases \(\mathrm{NH}_{3}\) and HBr produces \(\mathrm{NH}_{4} \mathrm{Br}\), a white solid. The two gases are introduced simultaneously at opposite ends of an evacuated glass tube that is \(1.0 \mathrm{~m}\) long. Calculate how far from the \(\mathrm{NH}_{3}\) end of the tube the white solid will form.

An ideal gas was contained in a glass vessel of unknown volume with a pressure of \(0.960 \mathrm{~atm} .\) Some of the gas was withdrawn from the vessel and used to fill a \(25.0-\mathrm{mL}\) glass bulb to a pressure of \(1.00 \mathrm{~atm}\). The pressure of the gas remaining in the vessel of unknown volume was 0.882 atm. All the measurements were done at the same temperature. Determine the volume of the vessel.

You are holding two balloons, an orange balloon and a blue balloon, both at the same temperature and pressure. The orange balloon is filled with neon gas and the blue balloon is filled with argon gas. The orange balloon has twice the volume of the blue balloon. Determine the mass ratio of Ne to Ar in the two balloons.

A container of gas has a pressure of \(550 .\) Torr. A chemical change then occurs that consumes half of the molecules present at the start and produces two new molecules for each three consumed. Calculate the new pressure in the container if \(T\) and \(V\) are unchanged.

The effects of intermolecular interactions on gas properties depend on \(T\) and \(P .\) Do these effects become more or less significant when each change occurs? Why? (a) A sealed container of gas is compressed to a smaller volume at constant temperature. (b) A container of gas has more gas added into the same volume at constant temperature. (c) The gas in a container of variable volume is heated at constant pressure.

Formaldehyde, \(\mathrm{CH}_{2} \mathrm{O},\) is a volatile organic compound that is sometimes released from insulation used in home construction, and it can be trapped and build up inside the home. When this happens, people exposed to the formaldehyde can suffer adverse health effects. The U. S. National Institute of Occupational Health and Safety (NIOSH) guideline for the maximum allowable concentration of formaldehyde in air in the workplace is \(16 \mathrm{ppb}\) (parts per billion) for an eight-hour average exposure. (a) Determine the partial pressure of formaldehyde at the maximum allowable level of \(16 \mathrm{ppb}\). (b) Calculate how many molecules of formaldehyde are present in each cubic centimeter of air when formaldehyde is present at \(16 \mathrm{ppb}\). (c) Calculate how many total molecules of formaldehyde are present in a room: \(15.0 \mathrm{ft}\) long \(\times 10.0 \mathrm{ft}\) wide \(X\) \(8.00 \mathrm{ft}\) high (at \(16 \mathrm{ppb}\) ).