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Friday 4/27

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**An Introduction to Gases**

Chapter 13

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**Kinetic Molecular Theory**

Postulate #1 Gases consist of tiny particles (atoms or molecules) Postulate #2 These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). Gases are COMPRESSIBLE

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**Kinetic Molecular Theory**

Postulate #3 The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas.

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**Kinetic Molecular Theory**

Postulate #4 The particles are assumed not to attract or to repel each other. Postulate #5 The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas.

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**Pressure What is pressure? How is it measured? mmHg (or Torr)**

Atmospheres (atm) Pascals (used in physics: 1 pascal = 1 newton per square meter) 4. psi Equivalences: 1 atm = 760 mmHg 1 atm = 101,325 Pa = kPa 1 atm = 14.7 psi

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**Pressure Pressure of air is measured with a BAROMETER**

(developed by Torricelli in 1643)

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**Pressure Calculation What is 475 mm Hg expressed in atm? 475 mm Hg**

= 0.625 atm 760 mm Hg

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**“The Law of Partial Pressure”**

Dalton’s Law “The Law of Partial Pressure” The total pressure of a mixture of gases is the sum of the partial pressures of the gases in the mixture. Ptotal = PA + PB + PC

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**Temperature Scales Celsius Kelvin 100 ˚C 0 ˚C 100˚C 373 K 273 K 100 K**

Boiling point of water 100 ˚C 0 ˚C 100˚C 373 K 273 K 100 K Freezing point of water Notice that 1 kelvin = 1 degree Celsius

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**Calculations Using Temperature**

ALL gas calculations require temperature in Kelvin T (K) = T(˚C) Body temp = 37 ˚C = 310 K Liquid nitrogen = ˚C = 77 K

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**Relationships How are temperature and volume related?**

How are volume and pressure related? How are pressure and temperature related?

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**Reminders Homework: Gases WS 1 Reminders: Extra Credit Due 5/11**

Test Corrections due 5/1

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**Monday and Tuesday 4/30 and 5/1**

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Warm Up When you increase the temperature in a container, do the particles of gas move faster or slower? Would this increase or decrease the pressure? What would happen if you put a balloon in the freezer? What would happen if you put a balloon in the oven? Is it possible to compress a gas?

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Demo Put a few drops of water in a can. Heat the can until the water boils. What is happening to the gas inside? Now flip the can over into cold water. Predict what do you predict will happen?

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On a Larger Scale The most common (and commonly collapsed) railcar is the DOT 111A100 class or commonly called a "general purpose" tank car. These cars are rated to a test pressure of 100 psig and a minimum burst pressure of 500 psig. Minimum carbon steel plate thickness is 7/16 inch. For a 23,000 gallon car, the tank length is about 55 feet. For comparison purposes the "heaviest" pressure car commonly used is a 105J500, rated to a test pressure of 500 psig and a minimum burst of 1250 psig. They are made of 1 inch thick, high-strength steel plate.

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On a Larger Scale

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Gas Laws Calculations Get out a calculator!!!

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**PV=nRT P = pressure ( atm or kPa ) V= volume ( L )**

The Gas Law PV=nRT P = pressure ( atm or kPa ) V= volume ( L ) n= number of moles (mol) T= temperature (K)

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**R – The Proportionality Constant**

Value depends on units 8.314 L (kPa) mol (K) 0.0821 L (atm) Or R is the proportionality constant Basically once scientists got the gas laws figured out, they put them all together but realized that the variables behaved according to this proportionality constant. Your value of R, like anything else, will vary depending on the units. Can’t add apples to oranges – If you have 3 apples and 5 oranges how many apples do you have? Because you can’t add apples to oranges. So to add them together you would need to convert to fruit for both and then add them together.

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**The Gas Law – Problem PV = nRT P = 1454.95 kPa P = 1500 kPa**

If 7.0 moles of an ideal gas has a volume of 12.0 L with a temperature of 300. K, what is the pressure in kPa? PV = nRT P (12.0 L) = (7.0 mol)(300 K) 8.314 L (kPa) mol (K) Using the Ideal Gas Law work through this problem with your neighbor. P = kPa P = 1500 kPa

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**The Gas Law – Problem 9.95 atm PV = nRT**

If 4.00 moles of a gas has a volume of 10.0 L with a temperature of 303. K, what is the pressure in atm? PV = nRT P (10.0 L) = (4.00 mol)(303 K) 0.0821 L (kPa) mol (K) Using the Ideal Gas Law work through this problem with your neighbor. 9.95 atm

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Combined Gas Law Let’s say we have a balloon full of O2 gas AND we change some conditions. Would there be anything similar between the two gases?

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**Combined Gas Law – Problem**

You have 3.0 moles of a solution at 300. K and 15 atm in a 2.0 L container. If the container is heated to 350. K and the volume decreased to 1.0 L, what will the new pressure be? P1 15 atm P2 want V1 2.0 L V2 1.0 L n1 3.0 moles n2 R1 constant R2 T1 300. K T2 350. K Work through this problem with your neighbor. What did everyone get? 35 atm, correct Let’s see how you got that: All work is on the powerpoint (click mouse)

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**Combined Gas Law – Problemc**

P1V1 = n1R1T1 P2V2 n2R2T2 If we know that R1 = R2 and the mass is constant then P1V1 = T1 P2V2 T2 Replace with numbers (15 atm)(2.0 L) = (300. K) P2(1.0L) (350. K)

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**Combined Gas Law – Problem**

(15 atm)(2.0 L) = (300. K) P2(1.0 L) (350. K) (15 atm)(2.0 L)(350. K) = P2 (1.0L)(300. K) P2 = 35 atm

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**P1V1 = P2V2 Pressure & Volume At constant Temperature**

Pressure and Volume vary inversely. Why? More collisions More pressure P1V1 = P2V2 P1V1 = n1R1T1 P2V2 n2R2T2 Smaller volume means particles have shorter distance to go to hit the sides of the container.

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**P & V – Example Problem 1.0 atm = P2**

If you start with L of a gas at 7.0 atm and you move the gas to a container with 3.5 L available, how much pressure will the gas exert? P1 (V1) = P2 (V2) 7.0 atm (0.500 L) = P2 (3.5 L) Work through this problem with your neighbor. What did everyone get? 1.0 atm, correct Let’s see how you got that: All work is on the powerpoint (click mouse) 7.0 atm (0.500 L) = P2 3.5 L 1.0 atm = P2

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**V1 = V2 T1 T2 Temperature & Volume At constant Pressure**

Volume & Temperature vary directly. Why? More collisions More Volume P1V1 = n1R1T1 P2V2 n2R2T2 Heating a gas will make it expand. ROOT BEER DEMO Also relate back to gases expanding to take up all space available. V1 = V2 T1 T2

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T & V – Example Problem If a gas is in a balloon with a volume of 12.0 L and at a temperature of 300. K, what will the volume be if you place the balloon in a freezer at 250. K? V1 = V2 T1 T2 12.0 L 300. K 250. K 12.0 L (250. K) 10.0 L Work through this problem with your neighbor. What did everyone get? 10.0 L, correct Let’s see how you got that: All work is on the powerpoint (click mouse)

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S.T.P. Standard Temperature and Pressure These are conditions that are universal Standard Temperature: 0ºC or K Standard Pressure: 1atm or kPa

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**S.T.P. – Example Problem PV = nRT V= 22.4 L**

What is the volume of 1 mole of a gas at STP? P 1 atm V want n 1 mole R (L)(atm)/(K)(mole) T 273 K PV = nRT (1atm)V = (1 mole)( [Latm/Kmole])(273K) V= 22.4 L

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Practice Problems The pressure of a sample of gas is 5.00 atm and the volume is 30.0 L. If the volume is changed to 50.0 L, what is the new pressure?

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Practice Problems A sample of gas has a volume of 50.0 L at a temperature of 300.K. What temperature would be needed for this sample to have a volume of 60.0 L if its pressure remains constant?

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Practice Problems A 3.68g sample of a certain diatomic gas occupies a volume of 3.00 L at 1.00 atm and a temperature of 45°C. Identify this gas.

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Quiz Time Have out a pencil and a calculator

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Cage of Death Lab Determine the volume of one mole of gas at STP Do prelab before class Lab write up due

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Reminders Homework: Gases WS 2 Cage of Death Pre-lab Reminders: Extra Credit Due 5/11

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**Wednesday and Thursday 5/2 and 5/3**

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Warm Up A sample of gas has a volume of 90.0 L at a temperature of 303.K. What temperature would be needed for this sample to have a volume of 70.0 L if its pressure remains constant?

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Cage of Death Lab Determine the volume of one mole of gas at STP Gas collection tube Balancing pressure Making cage

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Cage of Death Lab 2. Why is the length of the magnesium ribbon important? Think back to stoichiometry. 3. Be careful with the HCl – 3.0 M is very corrosive

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Cage of Death Lab 4. Why is it important that the HCl and H2O don’t mix? 5. Not too tight Not too loose

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Cage of Death Lab 6. 8. (F) Today’s atmospheric pressure is…

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**Cage of Death Lab 9. 10. Allow reaction to happen…**

How would a bubble effect your results? 10. Just right Too high Too low

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**Cage of Death Lab CLEAN UP Liquids down drain**

Repeat the lab for a second trial. CLEAN UP Liquids down drain Solids return to container

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**After Lab Done in lab? Reminders: Extra Credit due 5/11**

Work on Homework: Cage of Death Write Up Gases WS 3 Reminders: Extra Credit due 5/11

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Friday 5/4

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Warm Up A sample of gas is in a 13.0 L container with 1.26 atm of pressure on it at 23.5 ˚C. How many moles of gas are in the sample? If the gas in the problem above is released from its container into a 56.0 L container but the temperature remains constant, what will the new pressure be?

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Demos How does atmospheric pressure affect gas particles?

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Reminders Homework: Study for your test Reminders: Extra Credit Due 5/11 Gases Test 5/7 or 5/8

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