Chapter 11 Gases “We live immersed at the bottom of a sea of elemental air.” Evangelista Torricelli
Properties of Gases • Gases form homogeneous mixtures • Gases are compressible • All gases have low densities • air 0.0013 g/mL • water 1.00 g/mL • iron 7.9 g/mL • Gases expand to fill their containers uniformly • A gas exerts a pressure
Pressure • Defined as force per unit area
Pressure Units • 101.325 kPa • = 760 mmHg • =760 torr • =1 atm • =30 in Hg • =14.7 psi
Measurement of Pressure
The atmospheric pressure at the summit of Mt. McKinley (Denali) is 606 mm Hg on a certain day. What is the pressure in atmospheres?
The Gas Laws Jacques-Alexandre-César Charles(1746-1823) Amadeo Avogadro (1776-1856) Robert Boyle (1627-1691)
Boyles Law • The volume of a gas and its pressure are inversely proportional.
P1V1 = P2V2 • An inflated balloon has a volume of 0.55 L at sea level (1.0 atm) and is allowed to rise to a height of 6.4 km, where the pressure is about 0.40 atm. Assuming that the temperature remains constant, what is the final volume of the balloon?
P1V1 = P2V2 • A 1.04 L sample of gas at 759 mm Hg pressure is expanded until its volume is 2.24 L. What will be the pressure in the expanded gas sample if the temperature remains constant?
Charles’ Law • The volume (V) of a gas and its temperature (T) expressed in kelvin are directly proportional.
V1/T1=V2/T2 • A container of 452 mL of argon is heated from 22oC to 187oC at constant pressure. What is its final volume?
V1/T1=V2/T2 • Gas volume is sometimes used as a way to measure temperature. Suppose a sample of a gas in a thermometer has a volume of 135 mL at 11oC. What temperature would correspond to a volume of 113 mL?
Avogadro’s Law • The volume of a gas and the amount of the gas in moles(n) are directly proportional.
V1/n1=V2/n2 • If 3.25 mol of argon gas occupies a volume of 100.0 L at a particular temperature and pressure, what volume does 14.15 mol of argon occupy under the same conditions?
From V T Charles’ Law V n Avogadro Law V 1/P Boyle’s Law Get
Ideal Gas Law PV = nRT • P = pressure (typical units are atm or torr or mm Hg) • V = volume (typical units are L) • n = number of moles • T = temperature (must be in K) • R = gas constant = 0.0821 L atm/mol K • = 62.4 L torr/mol K
A sample of nitrogen gas kept at 32oC in a 2.3 L container exerts a pressure of 4.7 atm. Calculate the number of moles of gas present.
Calculate the volume in liters occupied by 7.40 g of CO2 at 735 torr and 25oC.
A bicycle tire has a pressure of 2000 torr in Death Valley when the temperature is 38oC. What would the pressure be if you took the bike to Lake Tahoe where the temperature was 0oC?
What will be the new volume if 125 mL of He gas at 100oC and 0.981 atm is cooled to 25oC and the pressure is increased to 1.15 atm?
Find the molar mass of an unknown gas that has a density of 1.45 g/L at 44oC and 0.331 atm.
Standard Temperature and Pressure (STP) • T = 0oC = 273K • P = 1 atm = 760 torr
Calculate the volume of 1.0 mole of a gas at STP. • What volume will 3.21 moles of Ne occupy at STP?
Calculate the density of Argon at STP.
Dalton’s Law of Partial Pressures Ptotal = P1 + P2 + P3 + ...... The total pressure of a gas mixture is equal to the sum of the pressures of the individual gases.
The atmosphere of Venus contains the following gases. • CO2 392 torr, • N2 834 torr • Ar 302 torr • What is the atmospheric pressure on Venus?
In 1774, Joseph Priestly heated mercury(II) oxide by using a lens to focus the rays of the sun on a sample of the red powder. It decomposed into its elements, and thus oxygen was discovered: • 2 HgO(s) 2 Hg(l) + O2(g) • Calculate the volume of oxygen, adjusted to STP, that is produced by decomposing 71.8 g HgO.
Dolomite, the white rock used in gardens, is a one to one combination of calcium and magnesium carbonate. Another use is the manufacture of refractory brick for lining very-high-temperature furnaces. It is processed through a rotary kiln in which carbon dioxide is driven off: CaCO3MgCO3(s) CaO(s) + MgO(s) + 2 CO2(g) • For each kilogram of dolomite processed, how many liters of carbon dioxide escape to the atmosphere at 264oC and 1.09 atm?
Sulfur burns to SO2 with a beautiful deep purple-blue flame, but with a foul, suffocating odor: 2 S(s) + O2(g) 2 SO2(g) • How many liters of O2 are needed to form 35.2 L SO2, both gases being measured at 741 torr and 26oC?
A 3/4 full propane tank has a pressure of 3.2 atm at a temperature of 25oC. If you put the tank in the back of your car for a barbecue at the beach and the temperature reaches 103oC, what is the new pressure of the propane in the tank?
What volume will 4.83 moles of a gas occupy at 35oC and 1.15 atm pressure?
The nitrogen gas in an air bag with a volume of 35 L, exerts a pressure of 850 mm Hg at 25oC. How many moles of N2 are in the bag?
Sulfur hexafluoride (SF6) is a colorless, odorless, very unreactive gas. Calculate the pressure (in atm) exerted by 1.82 moles of the gas in a steel vessel of volume 5.43 l at 69.5oC.
