Warmup A 40.0m 3 weather balloon at standard temperature encounters a sudden icy cool breeze during its journey into the Alaskan sky. If the weather balloon decreases to 37.9 m 3, calculate the temperature of the icy cool breeze. Assume pressure is held constant at 610 mmHg.

The Combined Gas Law and Dalton’s Law of Partial Pressures You have all the sample problems in your packet

P 1 V 1 = P 2 V 2 T 1 T 2 (101.3 kPa)(V 1 )=(99.0 kPa) (466 ml ) (273K) (-4.6°C+273) (101.3kPa)(V 1 )(268.4°K)=(99.0 kPa)(466 ml)(273K) (101.3 kPa)(268.4K) (101.3 kPa)(268.4K) V 1 = 460ml Ex1. A half-full water bottle (at STP) travels by car and is put in a freezer high up in the mountains, changing the temperature to -4.6° C. The volume changes to 466 ml and the pressure decreases to 99.0 kPa. What was the original volume of the gas inside the water bottle?

Ex 2: A helium balloon at standard, constant temperature is placed in a vacuum, decreasing the pressure to atm. The volume expands from 1.78 L to 4.98 L. What was the pressure of the balloon in the beginning? Use Boyle’s Law Use Combined Gas Law same answer…. I swear!

P 1 V 1 = P 2 V 2 T 1 T 2 P 1 (1.78 L)=(0.843 atm) (4.98 L) (273K) (273K) P 1 (1.78 L) (273K) =(0.843 atm)(4.98 L)(273K) (1.78 L) (273K) (1.78 L) (273K) P 1 = 2.36 atm

Ex 3: A helium-filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at atm and 10.°C? InitialAfter P 1 =P 2 = V 1 =V 2 = T 1 =T 2 = P1P1 T1T1 P2P2 T2T atm atm 50.0 L? 25°C 298 K 10.°C 283 K V 2 = V 2 = 60. L V1V1 V2V2

He CO 2 H2OH2O 0.7 atm 0.8 atm 2.3 atm Dalton’s Law of Partial Pressures the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases P total = P 1 + P 2 + P 3 + …

Ex 1: A container holds three gases: oxygen, carbon dioxide, and helium. The partial pressures of the three gases are 2.00 atm, 3.00 atm, and 4.00 atm, respectively. What is the total pressure inside the container? P total = P 1 + P 2 + P 3 + … P total = P O2 + + P CO2 + P He P total = 2.00 atm atm atm P total = 9.00 atm

Gas Collected Over Water: you need to account for the additional vapor pressure : P total = P gas + P H 2 O Note: most of the time, the total pressure is equal to the pressure inside the room!

Ex 2: Helium gas is collected over water at 25 °C. What is the partial pressure of the helium, given that the barometric pressure is mm Hg? P total = P He + P H 2 O mm Hg = P He mm Hg P He = mm Hg

Ex 3: A student has stored mL of neon gas over water on a day when the temperature is 28.0°C. If the barometer in the room reads mm Hg, what is the pressure of the neon in its container? P total = P Ne + P H 2 O mmHg = P Ne mm Hg P Ne = mm Hg

Ex 4: A container has two gases, helium and argon. Suppose that the mixture contains 30% helium by volume. Calculate the partial pressure of helium AND argon if the total pressure of the container is 4.00 atm. Total pressure = 4.00 atm. 30% of 4.00 is 1.2 atm (0.30 X 4.00 atm = 1.2 atm) 70 % of 4.00 is 2.8 atm (0.70 X 4.00 atm = 2.8 atm) P He = 1.2 atm AND P Ar = 2.8 atm Double Check: P total = P He + + P Ar P total = 1.2 atm atm = 4.00 atm

Ex 5: A certain mass of oxygen was collected over water when potassium chlorate was decomposed by heating. The volume of the oxygen sample collected was 720 mL at 25°C and an atmospheric pressure of 750 mmHg. What would the volume of the oxygen be at STP? P 1 V 1 = P 2 V 2 T 1 T 2 P 1 (720ml) = (760mmHg)V 2 ( ⁰ C) (273K) P total = P O2 + P H 2 O 750 mmHg = P O mmHg P O2 = mmHg Answer: 630 mL (726.2 mmHg)(720ml) = (760mmHg)V 2 (298K) (273K)

Mystery Game: The Gas Problem Strikes BACK Directions: You will be given three TIMED gas law problems. (Exactly 3 minutes to do each problem…so work together). Your job is to find an answer to each mystery problem. The sum of all three mystery problems, ignoring sig fig rules, is:

The volume of a gas at 27.0°C and atm is 80.0 mL. What volume will the same gas sample occupy at standard temperature and standard pressure? What pressure(atm) is required to reduce 60.0 mL of a gas at STP to 10.0 mL at a temperature of 25.0°C? A 250. mL sample of oxygen gas is collected over water at 25.0 °C and 760 mmHg. What is the pressure of the oxygen gas by itself?

add your answers to all 3 mystery problems and round to 3 sig figs! Mystery Problem #1 Mystery Problem #2 Mystery Problem #3 ANSWER (no units) ++= 14.6 mL atm mm Hg =