1. 1 Unit 10: Gases Chapter 14 Test: February 25, 2009

2. 2 The Mole

3. 3 Gas Stoichiometry  1 mole = 22.4 L of a gas at STP All stoichiometric calculations will be done at STP 222...

4. 4 STP  Standard temperature and pressure (STP) has been designated as: Temperature at 273 K Pressure at 1 atm 1 mole = 22.4 L  Used to compare gases  Creates ideal conditions for describing behavior of gases

5. 5 Gas Stoichiometry ? L H 2 = 25 mol H 2 x 22.4 L H 2 = 560 L H 2 1 1 mol H 2 Example #1 Volume  Moles There are 25 moles of hydrogen gas in a zeppelin. How many liters of hydrogen gas does it contain at STP?

6. 6 Gas Stoichiometry ? L O 2 = 1.5 L C 3 H 8 x 1 mol C 3 H 8 x 5 mol O 2 x 22.4 L O 2 = 7.5 L O 2 1 22.4 L C 3 H 8 1 mol C 3 H 8 1 mol O 2 Example #2 Volume  Volume When you are grilling steaks, how many liters of oxygen are required to burn 1.5 liters of propane in the reaction: C 3 H 8 + 5O 2  3CO 2 + 4H 2 O?

7. 7 Gas Stoichiometry ? g Fe 2 O 3 = 8.8 L O 2 x 1 mol O 2 x 4 mol Fe x 55.847 g Fe = 29.25 g Fe 2 O 3 1 22.4 L O 2 3 mol O 2 1 mol Fe Example #3 Volume  Mass How many grams of rust would be created from iron reacting with 8.8 L of oxygen gas in the reaction: 4Fe + 3O 2 → 2Fe 2 O 3 ?

8. 8 Gas Characteristics  Gases have no definite shape or volume  Gases diffuse rapidly  Gases have low density  Gases are compressible/expandable  Gases exert pressure on their containers

9. 9 Kinetic Molecular Theory  Explains the behavior of all matter (solids, liquids, and gases) at a particle level - kinetic means ‘motion’  As related to gases, there are several basic principles of kinetic molecular theory (KMT): 1.Gas particles are in constant, random motion 2.Gas particles do not attract or repel each other 3.Gas particles have elastic collisions, meaning they do not lose kinetic energy when they collide 4.Gas particles’ kinetic energy depends on their temperature

10. 10 Physical Properties: Temperature  Temperature is a measure of the average kinetic energy of particles in a system Different from heat - amount of energy in a system  Temperature is measured in units of: Fahrenheit ( o F) Celsius ( o C) Kelvin (K)  Temperature is measured by a thermometer How does temperature change? As a result of its change, what does it effect?

11. 11 Physical Properties: Temperature  When talking about gases, we never work with Celsius – only Kelvin!  Converting Celsius to Kelvin = ? o C + 273 Ex: Room temperature is about 22oC. In Kelvin, this would be 296 K. Absolute Zero (0 Kelvin or -273 o C) is the temperature at which all particle motion ceases Absolute zero can never be achieved artificially, though it is possible to reach temperatures close to it through the use of cryocoolers.

12. 12 Physical Properties: Volume  Volume is the space matter occupies  Gases always occupy the volume of their container  Volume of gas is measured in units of liters (L) or milliliters (mL)  1 L = 1000 mL  Gas volume can be expanded or compressed due to changes in… – Temperature – Pressure – Amount of particles (mass or moles) Describe the similarities and differences between the balloons. What accounts for their differences?

13. 13 Physical Properties: Pressure  Pressure is the force over a given area If someone stepped on your foot, which shoe would you prefer they wore? Pressure is measured in units of: – Atmospheres (atm) – Pascals (Newtons/m 2 ) Pressure is measured by 2 instruments: – Barometer – Manometer – psi (pounds per square inch) – mmHg (mm of Mercury)

14. 14 Physical Properties: Pressure  Gas pressure can be altered due to changes in… – Volume – Temperature – Amount of particles (mass or moles) Describe the similarities and differences between the two basketballs. What accounts for their differences?

15. 15 Gas Laws  The following laws explain the relationships between temperature, volume, and pressure: Dalton’s Law Boyle’s Law Charles’ Law Gay-Lussac’s Law Combined Gas Law Ideal Gas Law

16. 16 Dalton’s Law  The total pressure of a gas mixture is the sum of the partial pressures of each individual gas  Air is a mixture! I’m John Dalton

17. 17 Dalton’s Law  Ex: The pressure on a tank of air with… + 20.9 atm oxygen  78.1 atm nitrogen  0.97 atm argon  1.28 atm water vapor  0.05 atm carbon dioxide = 101.3 atm P total = P 1 + P 2 + P 3 …

18. 18 Boyle’s Law  Explains the effect pressure has on volume  Temperature stays constant Inverse relationship – As pressure increases, volume decreases  P  V – As pressure decreases, volume increases  P  V I’m Robert Boyle

19. 19 Boyle’s Law KMT connection: the less space particles have to move, the more forces they exert on each other

20. 20 Boyle’s Law  Math Practice: If the pressure is tripled, what happens to the volume? If the pressure is halved, what happens to the volume? Example: Squeezing syringe

21. 21 Charles’ Law  Explains the effect temperature has on volume  Pressure stays constant Direct relationship – As temperature increases, volume increases  T  V – As temperature decreases, volume decreases  T  V I’m Jacques Charles

22. 22 Charles’ Law KMT connection: the more avg. kinetic energy particles have, the greater the distance between particles (increasing volume)

23. 23 Charles’ Law  Math Practice: If the temperature is quadrupled, what happens to the volume? If the temperature is decreased by 1/3, what happens to the volume? Example: Hot air balloon

24. 24 Gay-Lussac’s Law  Explains the effect temperature has on pressure  Volume stays constant Direct relationship – As temperature increases, pressure increases  T  P – As temperature decreases, pressure decreases  T  P PP I’m Joseph Louis Gay-Lussac

25. 25 Gay-Lussac’s Law KMT connection: the more avg. kinetic energy particles have, the more forces they exert on each other

26. 26 Gay-Lussac’s Law  Math Practice: If the temperature is doubled, what happens to the pressure? If the temperature is decreased by 1/4, what happens to the pressure? Example: Pressure cooker

27. 27  The gas laws may be integrated into a single equation called the combined gas law  Where… P = pressure in atm V = volume in L T = temperature in K “1” means initial “2” means final  Steps to solving 1. Assign variables 2. Convert o C to K (if necessary) 3. “Drop” constants (see example) 4. Solve problem Combined Gas Law

28. 28 Combined Gas Law  Example: In the fall, at a temperature of 32 o C, you fill your tires to a pressure of 2.18 atm. A cold front blows through, with temperatures dropping to 5 o C, and your tires become flat. Knowing that the volume of your tires has not changed, what is the new pressure of the tires? P 1 = 2.18 atm V 1 = constant T 1 = 32 o C + 273 = 305 K P 2 = ? atm V 2 = constant T 2 = 5 o C + 273 = 278 K P 1 V 1 = P 2 V 2 2.18 atm = ? atm T 1 T 2 305 K 278 K P 2 = 1.987 atm What law best illustrates what happened to the tires in this problem?

29. 29 Ideal Gas Law  Ideals gases are theoretical models  Real gases behave like ideal gases at STP  The ideal gas law relates pressure, temperature, volume, and number of moles  Equation includes universal gas constant R, which “corrects” conditions to STP  Where… P = pressure in atm V = volume in L n = number of particles in moles R = universal gas constant T = temperature in K 0.821 L · atm mol · K

30. 30 Ideal Gas Law  Example: Tyler is scuba diving along a coral reef. Your 10 liter air tank contains 2 moles of oxygen gas at 20 o C. What is the pressure of your oxygen tank? P = ? atm V = 10 L n = 2 moles R = 0.821 L · atm mol · K T = 20 o C + 273 = 293 K PV = nRT ? atm * 10 L = 2 mol * 0.821 L · atm * 293 K mol · K P = 48.11 atm