1. Gasses… or Gases? Chapter 14

2. Gasses go “squish” Gasses are compressible, meaning their volume can decrease when pressure is applied. Gasses are compressible because there is so much space between them. – In normal air (1 atm), there is 10 times as much space between particles as each particle takes up. This picture is actually way too dense, but I couldn’t find a better one.

3. A reminder about pressure… Pressure is the amount of force in an area. – Measured in pascals (Pa) or kilopascals (kPa = 1000 Pa) Gas pressure is caused by collisions against a surface, like the side of a container.

4. What affects pressure? There are 4 variables used to describe a gas: – Pressure (P) Measured in kilopascals (kPa) – Amount of gas (n) Measured in moles (mol.) – Volume (V) Measured in liters (L) – Temperature Measured in kelvin (K)  not technically a degree.

5. Amount of Gas and Pressure As you add gas, two things can go up: – Either the volume can get higher (container expands) – Or the pressure goes up (more collisions) – Or both… If you double the particles, the volume or the pressure must double. This is how you inflate tires, balls, and air mattresses, too.

6. https://www.youtube.com/watch?v=2WJVHtF 8GwI https://www.youtube.com/watch?v=2WJVHtF 8GwI http://phet.colorado.edu/en/simulation/gas- properties http://phet.colorado.edu/en/simulation/gas- properties

7. Containers Non-flexible containers like SCUBA tanks will have the pressure go up. – Volume will not change. Semi-flexible containers like a beach balls will have volume AND pressure go up. Flexible containers like bubbles will increase in volume, but not pressure.

8. Volume and Pressure Demo

9. Volume and Pressure When you compress air and make the volume less, the pressure goes up. When volume goes up, pressure goes down. – “Inverse relationship” Twice the volume, means half the pressure. – P*V = a constant

10. Let’s try a couple… How much of a volume do you need to have to increase the pressure 5 times? How many times more gas do you need to have 3 times more pressure?

11. Okay, quick reminder… Pressure and amount of gas are DIRECTLY proportional – When one goes up, the other goes up. – P=kn (k is a constant, depending on volume and temperature) Pressure and volume are INVERSELY proportional – When one goes up, the other goes down. – PV=k (k is a constant, depending on temperature and moles)

12. Temperature and Pressure As temperature goes up, pressure also goes up – P=Tk k is constant for a certain volume and number of moles Temperature is always measured in Kelvin (K) !!!! As particles move faster, they move and bounce more. – Almost everything expands when it gets warmer, anyways.

13. Temperature and Pressure Demo For Tuesday

14. If you have a sealed container… Only 3 things can change: – (Because amount of gas can’t change, since it’s sealed) – Pressure – Volume – Temperature If you keep one the same, the other two will change together.

15. The Gas Laws Science’s “Laws” – Mathematical predictions (equations) that can’t be broken 3 that relate to pressure, volume, and temperature. Boyle’s Law – Volume and Pressure Charles’s Law – Temperature and Volume Gay-Lussac’s Law – Pressure and Temperature

16. Balloon in a vacuum demo

17. Boyle’s Law Starting pressure times starting volume equals ending pressure times ending volume – P 1 *V 1 = P 2 *V 2 INVERSE! – P 1 /P 2 = V 2 /V 1 See how they’re flipped? – INVERSE! » INVERSE!

18. Okay, let’s try some P 1 *V 1 = P 2 *V 2 I have a container that is 30mL, and it is at 1 atm of pressure. I want it to have 6 atm of pressure. How many mL must my container be?

19. Okay, let’s try some P 1 *V 1 = P 2 *V 2 I have a container that is 30mL, and it is at 1 atm of pressure. I want it to have 6 atm of pressure. How many mL must my container be? A tennis ball has about 1.5 atm in it. It has a volume 58mL. When you hit it with a racket, it decreased in volume to 30.mL. What is the pressure inside the tennis ball when you hit it?

20. Balloon Demo Maybe heated can if we have enough time

21. Charles’s Law (Or Charles’) Or Chuck’s Law, I guess. In a flexible enclosed container (like a balloon) as the temperature decreases, the volume will also decrease. – All the temperatures MUST BE in Kelvin!!!! V 1 /T 1 = V 2 /T 2 V 1 *T 2 = V 2 *T 1 V 1 /V 2 = T 1 /T 2 – You only need to know one of these, and you can solve for any of them.

22. Some Charles’s Law Problems You have a balloon with a volume of 25.0mL at 370.K, and you cool it down to 280.K. What is the new volume of the balloon?

23. Some Charles’s Law Problems You have a balloon with a volume of 25.0mL at 370K, and you cool it down to 280K. What is the new volume of the balloon? You have a 300.0L drum that you want to collapse to only 30.0L. It is currently 25.0°C. What temperature do you need to get it down to? Answer in Kelvin and °C.

24. Boyle vs. Charles Boyle’s: – Pressure and Volume are INVERSE. Multiplied together Charles’s: – Temperature and Volume are DIRECT Divide one by the other Divide = Direct B comes before C – Pressure comes before Temperature – BP and CT

25. http://ed.ted.com/lessons/1207-1-a-bennet- brianh264 http://ed.ted.com/lessons/1207-1-a-bennet- brianh264

26. Gay-Lussac’s Law When volume is constant (like in a rigid container) the pressure and temperature are directly proportional – When one goes up, the other goes up. P 1 /T 1 = P 2 /T 2 – Direct = divide – Temperature STILL must be in Kelvin! Kelvin! KELLLVINNN!

27. You want a problem? I got your problems right here, buddy. P 1 /T 1 = P 2 /T 2 You have a SCUBA tank that starts at 1000. kPa, and you want it to have 7000.kPa inside of it. If you start at 293K, what temperature must you heat it up to?

28. You want a problem? I got your problems right here, buddy. P 1 /T 1 = P 2 /T 2 You have a SCUBA tank that starts at 1000kPa, and you want it to have 7000kPa inside of it. If you start at 293K, what temperature must you heat it up to? You have a can of propane that is at 300.kPa at 15°C. It heats up to 30.°C in the sun. What is the new pressure?

29. The Combined Gas Law If you combined these three laws, you can get one “mega-law” that includes all 3 (temperature, volume, and pressure) This allows you to calculate how much of one measurement you have, if you know the other 5! – It also makes it so you don’t really need to know the other 3 equations.

30. Using the Combined Gas Law If something stays the same (“constant”) just cancel it out from both sides of the equation. If all 3 (temperature, pressure and volume) change, then use all the variables and solve for the unknown. Got it?

31. Okay, let’s try some.

32. No.

33. Okay, let’s try some. Yes.

34. Okay, let’s try some. Fine… Ugh, whatever.

35. Okay, let’s try some. Solve with the Combined Gas Law: If the temperature remains constant, but the pressure increases from 100.kPa to 300.kPa, how much would the volume decrease to if it started at 230.L?

36. Okay, let’s try some. Solve with the Combined Gas Law: Original measurements: – Pressure: 37.1 atm – Volume: 22.5 mL – Temperature: 250.0 K New measurements: – Pressure: ? – Volume: 30.2 mL – Temperature: 270.0 K

37. How we all feel right now. http://www.tagtele.com/videos/voir/24776 (2:49)

38. All the gas laws in one. P*V (Boyle’s Law) V/T (Charles’s Law) P/T (Gay-Lussac’s Law) V/n (Avegadro’s Law of Volume 1 mole = 22.4) – N= moles Put them all together you get…

39. What was noticed… When you calculate PV/nT, you always got the same number. – Or very, very close. THE gas constant (R) !!! – Calculated using moles, kPa, Liters, and Kelvin. So, let’s calculate it, using Mr. V’s (wife’s) SCUBA tanks!

40. In each of the groups 1 person will be the pressure person – Use the pressure gauge on the tank – Convert psi into kPa (1 psi = 6.895 kPa) 1 person will be moles – Use the scale, with one empty tank and one full tank. The difference is the mass of the air inside. – Use the molar mass (g/mol) of dry air. (28.97 g/mol.). – Determine the moles be dividing mass in g by molar mass. 1 person will be temperature – Only the temperature of the full tank “matters”. – Use the temperature gun, convert to Kelvin. 1 person will be volume – Get the data from Faber’s e-mail on my website, facebook or twitter feed. Give the volume in Liters. If someone is missing, combine the bottom 2 jobs.

41. How to organize… All the moles people meet at the periodic table of the elements. (Find the molar mass using a portable electronic or the periodic table). All of the volume people, get together near the door, and find out the answer from the internet. Phone? Computer? iPad? All of the Pressure people, meet near the safety shower. All the Temperature people meet in the middle of the room. AT THE END, GET BACK TOGETHER, AND CALCULATE “R” = PV/nT

42. The Ideal Gas Law PV=nRT – But can be written to solve for any of them. – For example: T = PV/nR, V= nRT/P P 1 V 1 = P 2 V 2 n 1 RT 1 n 2 RT 2 – The R’s are the same, so they cancel out, and you end up with P 1 V 1 /n 1 T 1 = P 2 V 2 /n 2 T 2 Remember units are important now: – Pressure in kPa – Temperature in K – Volume in L – Amount in moles – R is 8.31

43. Ideal Gas Problems! PV=nRT How much pressure would you have, if you have a 4.00L container at 275K that is holding 3.75 moles?

44. Ideal Gas Problems! PV=nRT How much pressure would you have, if you have a 4.00L container at 275K that is holding 3.75 moles? How many moles would you need, to fill a 750mL container, with a pressure of 3.00 atm, at 22°C?

45. Ideal gasses vs. real gasses Most gasses act the same as ideal gasses. – Except at: Low temperatures High pressures – So, we can use the ideal gas laws at all times, except for when temperatures are really low or pressure is really high. Basically, all the time.

46. Partial Pressures in Gas Mixes Almost no gasses are pure, and instead are mixes of two or more types of particles. – Ex) There is mostly nitrogen in air, but it is also oxygen, carbon dioxide, argon, and more. Each gas exerts a pressure on its own, called a partial pressure. The gas pressure is a total of all the partial pressures in a gas. – “Dalton’s Law of Partial Pressure”

47. Dalton’s Law Problems What is the total pressure if the partial pressure of oxygen is 32.1 kPa, nitrogen is 106.4 kPa, and argon is 12.2 kPa?

48. Dalton’s Law Problems What is the total pressure if the partial pressure of oxygen is 32.1 kPa, nitrogen is 106.4 kPa, and argon is 12.2 kPa? If you have 1.000 atm of air, and you know that 81.1 kPa is nitrogen, and 18.3 kPa is oxygen what is the amount of air in kPa and atm that is NOT nitrogen or oxygen?

49. How Gasses Move Diffusion – Gasses move from areas of high concentrations to lower concentrations. Atoms move away from similar atoms. Effusion – Gasses move through small holes.

50. http://www.youtube.com/watch?v=H7QsDs8Z RMI http://www.youtube.com/watch?v=H7QsDs8Z RMI http://www.youtube.com/watch?v=0uBK7VxT 00E http://www.youtube.com/watch?v=0uBK7VxT 00E

51. Graham’s Law of Effusion The rate of effusion of a gas is inversely proportional to the square root of the mass of the gas. – If we know the molar masses of two gasses, we can compare their effusion rates. Notice how the v and m are SWITCHED!!!

52. Graham’s Law Problems! How many times faster does hydrogen gas move than nitrogen gas?

53. Graham’s Law Problems! How many times faster does hydrogen gas move than nitrogen gas? How many times faster does oxygen gas move compared to Krypton gas?

54. https://www.youtube.com/watch?v=BxUS1K7 xu30&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQ Q8oGr https://www.youtube.com/watch?v=BxUS1K7 xu30&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQ Q8oGr