Chapter 6

What is pressure? What causes pressure?

Explain what happens when a person inhales. What forces air into the lungs?

Explain what happens when a person exhales. What forces air out of the lungs?

What are the common units of pressure? List them in order of smallest to largest unit.

Summarize each of the simple gas laws (Boyle's law, Charles's law, and Avogadro's law). For each, explain the relationship between the two variables and also state which variables must be kept constant.

Explain why people may experience ear pain after a rapid change in altitude.

Explain why scuba divers should never hold their breath when they ascend to the surface.

Why is it impossible to breathe air through an extra-long snorkel (longer than a couple of meters) while swimming under water?

Explain why hot-air balloons float above the ground and why the second story of a two-story home is often warmer than the ground story.

Explain how the ideal gas law contains within it the simple gas laws (show an example).

Define molar volume and list its value for a gas at STP.

What is partial pressure? What is the relationship between the partial pressures of each gas in a sample and the total pressure of gas in the sample?

Why do deep-sea divers breathe a mixture of helium and oxygen?

What are the basic postulates of kinetic molecular theory? How does the concept of pressure follow from kinetic molecular theory?

How is the kinetic energy of a gas related to temperature? How is the root mean square velocity of a gas related to its molar mass?

Describe how the molecules in a perfume bottle travel from the bottle to your nose. What is mean free path?

Explain the difference between diffusion and effusion. How is the effusion rate of a gas related to its molar mass?

Deviations from the ideal gas law are observed at high pressure and low temperature. Explain this in light of kinetic molecular theory.

The pressure in Denver, Colorado (elevation \(5280 \mathrm{ft}\) ), averages about 24.9 in Hg. Convert this pressure to each indicated unit. a. atm b. \(\mathrm{mmHg}\) c. psi d. Pa

The pressure on top of Mount Everest ( \(29,029 \mathrm{ft}\) ) averages about \(235 \mathrm{mmHg}\). Convert this pressure to each indicated unit. a. torr b. psi c. in Hg d. atm

The North American record for highest recorded barometric pressure is 31.85 in \(\mathrm{Hg}\), set in 1989 in Northway, Alaska. Convert this pressure to each indicated unit. a. \(\mathrm{mmHg}\) b. atm c. torr d. kPa (kilopascals)

The world record for lowest pressure (at sea level) was \(652.5 \mathrm{mmHg}\) recorded inside Typhoon Tip on October \(12,1979,\) in the western Pacific Ocean. Convert this pressure to each indicated unit. a. torr b. atm c. in Hg d. psi

A sample of gas has an initial volume of \(13.9 \mathrm{~L}\) at a pressure of 1.22 atm. If the sample is compressed to a volume of \(10.3 \mathrm{~L}\) what is its pressure?

A balloon contains 0.158 mol of gas and has a volume of 2.46 L. If an additional \(0.113 \mathrm{~mol}\) of gas is added to the balloon (at the same temperature and pressure), what is its final volume?

A cylinder with a moveable piston contains \(0.553 \mathrm{~mol}\) of gas and has a volume of \(253 \mathrm{~mL}\). What is its volume if an additional \(0.365 \mathrm{~mol}\) of gas is added to the cylinder? (Assume constant temperature and pressure.)

What is the pressure in a 10.0 -L cylinder filled with 0.448 mol of nitrogen gas at a temperature of \(315 \mathrm{~K} ?\)

What is the pressure in a 15.0 -L cylinder filled with 32.7 g of oxygen gas at a temperature of \(302 \mathrm{~K} ?\)

A cylinder contains 28.5 L of oxygen gas at a pressure of 1.8 atm and a temperature of 298 K. How much gas (in moles) is in the cylinder?

An automobile tire has a maximum rating of 38.0 psi (gauge pressure). The tire is inflated (while cold) to a volume of \(11.8 \mathrm{~L}\) and a gauge pressure of 36.0 psi at a temperature of \(12.0^{\circ} \mathrm{C} .\) On a hot day, the tire warms to \(65.0^{\circ} \mathrm{C}\), and its volume expands to \(12.2 \mathrm{~L} .\) Does the pressure in the tire exceed its maximum rating? (Note: The gauge pressure is the difference between the total pressure and atmospheric pressure. In this case, assume that atmospheric pressure is 14.7 psi.)

A weather balloon is inflated to a volume of \(28.5 \mathrm{~L}\) at a pressure of \(748 \mathrm{mmHg}\) and a temperature of \(28.0^{\circ} \mathrm{C}\). The balloon rises in the atmosphere to an altitude of approximately \(25,000 \mathrm{ft}\), where the pressure is \(385 \mathrm{mmHg}\) and the temperature is \(-15.0^{\circ} \mathrm{C} .\) Assuming the balloon can freely expand, calculate the volume of the balloon at this altitude.

Aerosol cans carry clear warnings against incineration because of the high pressures that can develop upon heating. Suppose that a can contains a residual amount of gas at a pressure of \(755 \mathrm{mmHg}\) and a temperature of \(25^{\circ} \mathrm{C}\). What would the pressure be if the can were heated to \(1155^{\circ} \mathrm{C}\) ?

A sample of nitrogen gas in a 1.75-L container exerts a pressure of 1.35 atm at \(25^{\circ} \mathrm{C}\). What is the pressure if the volume of the container is maintained constant and the temperature is raised to \(355^{\circ} \mathrm{C}\) ?

Use the molar volume of a gas at STP to determine the volume (in L) occupied by \(33.6 \mathrm{~g}\) of neon at \(\mathrm{STP}\).

Use the molar volume of a gas at STP to calculate the density (in \(\mathrm{g} / \mathrm{L}\) ) of nitrogen gas at \(\mathrm{STP}\).

A 248-mL gas sample has a mass of \(0.433 \mathrm{~g}\) at a pressure of \(745 \mathrm{mmHg}\) and a temperature of \(28^{\circ} \mathrm{C}\). What is the molar mass of the gas?

A 113-mL gas sample has a mass of \(0.171 \mathrm{~g}\) at a pressure of \(721 \mathrm{mmHg}\) and a temperature of \(32^{\circ} \mathrm{C}\). What is the molar mass of the gas?

A sample of gas has a mass of \(38.8 \mathrm{mg}\). Its volume is \(224 \mathrm{~mL}\) at a temperature of \(55^{\circ} \mathrm{C}\) and a pressure of 886 torr. Find the molar mass of the gas.

A sample of gas has a mass of \(0.555 \mathrm{~g}\). Its volume is \(117 \mathrm{~mL}\) at a temperature of \(85^{\circ} \mathrm{C}\) and a pressure of \(753 \mathrm{mmHg} .\) Find the molar mass of the gas.

Consider the chemical reaction: $$ \mathrm{C}(s)+\mathrm{H}_{2} \mathrm{O}(g) \longrightarrow \mathrm{CO}(g)+\mathrm{H}_{2}(g) $$ How many liters of hydrogen gas are formed from the complete reaction of \(15.7 \mathrm{~g}\) C? Assume that the hydrogen gas is collected at a pressure of \(1.0 \mathrm{~atm}\) and a temperature of \(355 \mathrm{~K}\).

Lithium reacts with nitrogen gas according to the reaction: $$ 6 \mathrm{Li}(s)+\mathrm{N}_{2}(g) \longrightarrow 2 \mathrm{Li}_{3} \mathrm{~N}(s) $$ What mass of lithium (in g) reacts completely with \(58.5 \mathrm{~mL}\) of \(\mathrm{N}_{2}\) gas at \(\mathrm{STP} ?\)

Consider a 1.0-L sample of helium gas and a 1.0-L sample of argon gas, both at room temperature and atmospheric pressure. a. Do the atoms in the helium sample have the same average kinetic energy as the atoms in the argon sample? b. Do the atoms in the helium sample have the same average velocity as the atoms in the argon sample? c. Do the argon atoms, because they are more massive, exert a greater pressure on the walls of the container? Explain. d. Which gas sample has the faster rate of effusion?

A flask at room temperature contains exactly equal amounts (in moles) of nitrogen and xenon. a. Which of the two gases exerts the greater partial pressure? b. The molecules or atoms of which gas have the greater average velocity? c. The molecules or atoms of which gas have the greater average kinetic energy? d. If a small hole were opened in the flask, which gas effuses more quickly?

We separate U- 235 from U- 238 by fluorinating a sample of uranium to form UF \(_{6}\) (which is a gas) and then taking advantage of the different rates of effusion and diffusion for compounds containing the two isotopes. Calculate the ratio of effusion rates for \({ }^{238} \mathrm{UF}_{6}\) and \({ }^{235} \mathrm{UF}_{6} .\) The atomic mass of \(\mathrm{U}-235\) is \(235.054 \mathrm{amu}\) and that of U-238 is 238.051 amu.

Calculate the ratio of effusion rates for Ar and \(\mathrm{Kr}\).

Which postulate of the kinetic molecular theory breaks down under conditions of high pressure? Explain.

Which postulate of the kinetic molecular theory breaks down under conditions of low temperature? Explain.

Use the van der Waals equation and the ideal gas equation to calculate the pressure exerted by \(1.000 \mathrm{~mol}\) of \(\mathrm{Cl}_{2}\) in a volume of \(5.000 \mathrm{~L}\) at a temperature of \(273.0 \mathrm{~K}\). Explain why the two values are different.

A 2.85-g sample of an unknown chlorofluorocarbon decomposes and produces \(564 \mathrm{~mL}\) of chlorine gas at a pressure of \(752 \mathrm{mmHg}\) and a temperature of \(298 \mathrm{~K}\). What is the percent chlorine (by mass) in the unknown chlorofluorocarbon?

The mass of an evacuated \(255 \mathrm{~mL}\) flask is \(143.187 \mathrm{~g}\). The mass of the flask filled with 267 torr of an unknown gas at \(25^{\circ} \mathrm{C}\) is \(143.289 \mathrm{~g} .\) Calculate the molar mass of the unknown gas.

A gaseous hydrogen- and carbon-containing compound is decomposed and found to contain \(85.63 \% \mathrm{C}\) and \(14.37 \% \mathrm{H}\) by mass. The mass of \(258 \mathrm{~mL}\) of the gas, measured at STP, was 0.646 g. What is the molecular formula of the compound?