Chemistry I Unit 9, Gases

Chemistry I – Unit 9, Gases

Chapter 13 States of Matter Chapter 14 The Behavior of Gases

Section Pages Questions 13.1- The nature of gases 385-389 p. 389 # 6 14.1- Properties of gases 413-417 p. 417 # 2, 3 14.2- The gas laws 418-425 p. 425 # 20 14.3- Ideal gases 426-429 p. 429 # 29 14.4- Gases: Mixtures and 432-434 (skip 435-436) p. 436 no questions movements Review p. 439 # 46, 47, 48, 56, 58

Useful conversion factors:

Kelvin temperature = C + 273

Universal Gas Law Constant (R):

0.08205 (L)(atm) 8.31 (L)(KPa) (mole)( K ) (mole)( K )

82.05 (mL)(atm) (mole)( K )

62.36 (L)(mm) (mole)( K )

STANDARD TEMPERATURE AND PRESSURE (STP):

Temperature: T = 0C, or 273K

Pressure (equal to any quantity below):

1 atmosphere 33.9 ft of H2O 0.760 meters of Hg 101,325 newtons/m2 76 cm of Hg 1.013 X 105 Pa 760 mm of Hg 101.3 KPa 760 torr 1013.25 mbar 29.92 in. of Hg 14.69 lb/in2

1 BOYLE’S LAW: Volume of a gas varies inversely with its pressure if the temperature is held constant.

P1V1 = P2V2

1) A sample of O2 occupies a volume of 250.0 mL at 2) a sample of CO2 occupies a volume of 3.50 L at 740 torr pressure. What is its volume at 800 torr? 125 kPa pressure. What is the pressure is the volume is decreased to 2.00 L?

3) A 2.00 L container of N2 had a pressure of 3.2 atm. 4) Ammonia gas occupies a volume of 450 mL at 720 What volume is necessary to decrease the pressure to mm Hg. What volume will it occupy at standard 1.0 atm? pressure? 5) A 175.0 mL sample of neon had it pressure 6) A sample of hydrogen at 1.50 atm had its pressure changed from 75 kPa to 150 kPa. What is its new decreased to 0.500 atm producing a new volume of volume? 750 mL. What was its original volume? 7) Chlorine gas occupies a volume of 1.23 L at 720 8) Fluorine gas exerts a pressure of 120 kPa. When torr. What volume will it occupy at 1.3 atm pressure? the pressure is changed to 1.50 atm, its volume is 250.0 mL. What is the original volume?

CHARLES’ LAW Charles’ law states that the volume of a gas varies directly with the Kelvin temperature, with constant pressure. V V 1  2 K = oC + 273 T1 T2

1) A sample of N2 occupies a volume of 250.0 mL at 2) Oxygen gas is at a temp. of 40˚C when it occupies 25oC. What is its volume at 95.0oC? a volume of 2.30 L. To what temp. should it be raised to occupy a volume of 6.50L?

3) H2 gas was coold from 150.˚C to 50.˚C. Its new 4) Cl2 gas occupies a volume of 25.00 mL at 300 K volume is 75.0 mL, what is the original volume? exactly. What volume will it occupy at 600 K?

5) A sample of Ne gas at 50˚C and a volume of 2.5 L 6) F2 gas at 300 K occupies a volume of 500.0 mL. is cooled to 25˚C. What is the new volume? To what temp. must it be taken to bring the volume to 325.0 mL? 7) He occupies a volume of 3.8 L at -45˚C. What 8) A sample of Ar gas is cooled at its volume went volume will it occupy at 45˚C? from 380.0 mL to 250.0 mL. If the final temp. was -55˚C, what was the original temp.?

COMBINED GAS LAW

2 In practical terms, it is often difficult to hold any of the variables constant. When there is a change in pressure, volume and temperature, the combined gas law is used.

P1V1 P2V2 = OR P1V1T2 = P2V2T1 T1 T2

1) A sample of gas has an initial pressure of 1.50 atm at a volume of 3.40 L at a temperature of 20.0C. If the temperature is increased by 10.0C and the pressure increases to 2.50 atm, what is the final volume?

2) A container of argon has a pressure of 720 torr and a volume of 256 mL at 25.0C. What is the pressure of the argon if the volume changes to 2.23 L and the temperature increases to 50.0C?

3) A flexible container holds a volume of 2.34 L of carbon dioxide at pressure and temperature of 652 mm Hg and 22.0C. If the pressure changes to 1.5 atm and the volume becomes 1340 mL, what is the new temperature of the carbon dioxide gas?

4) The initial volume and pressure of a gas is 90.5 kPa and 4.56 L. If the conditions change so the gas now has a pressure of 780 torr, a volume of 6.54 L and a temperature of 198C, what was the initial temperature?

5) A sample of helium occupies 135 mL at 22.5C. The pressure is 165 mm Hg. What is the pressure of the gas sample when it is placed in a 252 mL container at a temperature of 0.0C?

6) A rigid container has a sample of nitrogen gas with a volume of 500 mL, a pressure of 67.5 mm Hg and a temperature of 25.0C. What is the pressure of the gas if the temperature is raised to 80.0C?

7) A balloon has a volume of 45 mL at a pressure of 1.2 atm. If the temperature remains constant and the pressure on the outside of the balloon is increased to 3.4 atm, what is the new volume of the balloon?

8) A scuba tank contains air at a pressure of 235 kPa at a temperature of 25C. What will the pressure in the tank be if the temperature is lowered to 0C?

DALTON’S LAW OF PARTIAL PRESSURES

Ptotal = P1 + P2 + P3 + …

1. A container holds three gases: oxygen, carbon dioxide, and helium. The partial pressures of the three gases are 2.0 atm, 3.0 atm, and 4.0 atm respectively. What is the total pressure inside the container?

2. 2.0 L of N2 at 1 atm, 5.0 L of H2 at 5.0 atm and 3.0 L of O2 at 2.0 atm are mixed and transferred to a 10.0 L vessel. What is the resulting pressure?

3. A bulb containing He at 145 mm Hg is connected by a valve to a 2.0 L bulb containing Ar at 355 mm Hg (see figure below). Calculate the partial pressure of each gas and the total pressure after the valve between the bulbs is opened. (Assume the volume of the connecting tube is negligible.)

3 IDEAL GAS LAW

PV = nRT where P = pressure V = volume n = number of moles of gas R = universal gas constant T = Kelvin temperature

1) How many moles of O2 will occupy a volume of 2.50 L at 1.20 atm and 25˚C?

2) What volume will 2.04 moles of N2 occupy at 720 mm Hg and 20.00˚C?

3) What pressure will be exerted by 25.0 g of CO2 at a temperature of exactly 25˚C and a volume of 450.0 mL?

4) How many moles of nitrogen gas will occupy a volume of 347 mL at 6680.0 torr and exactly 27˚C?

5) What volume will 10.0 g of hydrogen (Remember: BrINClHOF) occupy at 1.05 atm and 25˚C?

6) Find the number of grams of CO2 that exert a pressure of 785 torr at a volume of 32.5 L and a temperature of 32˚C.

7) What is the molar mass of a 1.25 g sample of a gas that occupies a volume of 1.00 L at a pressure of 730 torr and a temperature of 27.0˚C?

8) If 16 g of a gas has a volume of 5.6 L at STP, what is its molecular weight (molar mass)?

9) An elemental gas (that means a gas that is on the periodic table) has a mass of 10.3 g. If the volume is 58.4 L and the pressure is 758 torr at a temperature of 2.5˚C, what is the gas?

GAS DENSITY PROBLEMS

PMM D = RT

1) Calculate the density of HCl at STP.

2) The density of a gas is 1.26 g/L at STP. What is the mass of 1 mole? What could this gas be?

3) What is the density of NH3 at 150.0 kPa and 25˚C?

4 4) If the density of a gas is 1.2 g/L at 122.0 kPa and 20.0˚C, what is the molar mass of the gas?

5) In the Macy's Thanksgiving day parade, 2000, there was a new float, the Cheerios' bee, Buzzbee. The jar of honey it was holding contained 36,763 L of helium. If the density of helium is 0.178 g/L, what is the mass of the helium for the jar of honey in Kg?

STOICHIOMETRY PROBLEMS WITH GASES

1. 200.0 g of sodium chloride are electrolyzed (decomposed). How many grams of sodium and what volume of chlorine gas are produced at STP?

2 NaCl  2 Na + Cl2

2. What volume of oxygen gas in liters can be collected at 0.987 atm pressure and 25.0˚C when 30.6 g of KClO3 decomposes by heating?  2 KClO3  2 KCl + 3 O2

3. How many liters of H2 gas at STP can be produced by the reaction of 4.60 g of Na and excess water?

2 Na + 2 H2O  H2 + 2 NaOH

REVIEW:

Draw the Lewis structure, name the shape of the molecule, and tell whether it is a polar or nonpolar molecule for the following:

H2O PCl3 CO2 CH4 HCl

Name the following:

CaCl2 FeSO4 NaNO3 NiPO4

P2O5 Fe2O3 CsBr PCl3