The Gas Laws!

1. The Gas Laws! Ch 14 Notes

2. Properties of Gases • Gases are compressible because of the space between particles. • Factors that affect gases: • Pressure • Volume • Temperature • # of moles present

3. Boyle’s Law • P1V1 = P2V2 • Inverse Relationship • T is constant • If one goes up, the other goes down • If one goes down, the other goes up

4. Lung model, marshmellows, bell jar, crush the can

6. Boyle’s Law Sample Prob • You and your crazy friend want to make funny voices using helium. You obtain a helium tank…. The volume of the gas in the tank is 2 L, but can fill over 200 L at room pressure. Room pressure is 1 atm, what was the original pressure?

7. Charles’ Law • V1/T1 = V2/T2 • Direct Relationship • P is constant • Temp in Kelvin!!! (°C + 273) • As one goes up, so does the other • As one goes down, so does the other • higher temp = more kinetic energy, more collisions, so volume increases

9. Charles’ Law Sample Prob • The temperature in the supermarket is a frosty 15 °C. When you buy your bag of chips it occupies 1 L of space. You leave the chips in your car for 1 hour and it reaches a temperature of 27 °C. what is the new volume of the bag?

10. Gay-Lussac’s Law • P1/T1 = P2/T2 • Direct Relationship • Temp in Kelvin!!! • Volume is constant • Sample: The temperature of a gas goes from 30 °C to 50 °C. The starting pressure is 760 mm Hg, what is the ending pressure?

11. Go To Absolute Zero Video Clip

12. Combined Gas Law • P1V1/T1 = P2V2/T2 • Combines Boyle’s, Charles’, and Gay-Lussac’s Laws • Sample: Your mom gives you a balloon that says “I love you!” (awh!). When she hands it to you it has a pressure of 1.5 atm and is at 295 K. The next morning it is at 290 K, has a pressure of 1.2 atm and has a volume of 1.5 L. What was the original volume of the balloon?

13. Molar Volume • At STP, 1 mole of any gas occupies 22.4 L • STP = 0 °C (273 K) and 1 atm • What will the volume of 5 moles of gas be at STP? • A sample of gas occupies 11.2 L at STP, how many moles is in the sample? • How many atoms are in 5 L of gas at STP?

14. Ideal Gas Law • relates P, V, T, and number of moles (n) • PV = nRT • R = 0.0821 (L*atm)/(mol*K) = “ideal gas law constant” • ‘ideal’ gases - particles have no volume & no attractive forces • real gases are ‘ideal’ gases under all conditions except very high pressure or very low temperature go to animation

15. Sample Problems… • You have 4 moles of helium gas at 1.5 atm and 25 L, what is the temperature? • How many moles of argon gas are present in 500 mL at 3 atm and 30 ºC?

16. Gas Stoichiometry • Coefficients in balanced reaction equations are mole ratios AND gas volume ratios! • Can do “vol to vol” stoichiometry when P and T are constant

17. Volume - Volume Gas Stoich (These are just like mole to mole problems - one conversion!) How many liters of NH3 will be produced if 10 liters of N2 are consumed according to the following reaction: N2 (g) + 3H2 (g) -----> 2NH3 (g)

18. Volume-Mass Gas Stoich Example N2 (g) + 3H2 (g) -----> 2NH3 (g) How many grams of hydrogen gas are required to create 20 L of ammonia gas if the above reaction occurs at STP? *do volume to volume stoich, then molar volume, then molar mass.

19. Mass-Volume Gas Stoich Example N2 (g) + 3H2 (g) -----> 2NH3 (g) How many liters of ammonia gas can be created from 50 grams of nitrogen gas at STP? *mass to mole stoich, then molar volume