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Introduction to Gas Laws

Introduction to Gas Laws. Definitions. Pressure - the exertion of a force upon a surface by an object in contact with it (force per unit area) Volume -the amount of 3-dimensional space occupied by an object

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Introduction to Gas Laws

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  1. Introduction to Gas Laws

  2. Definitions • Pressure - the exertion of a force upon a surface by an object in contact with it (force per unit area) • Volume -the amount of 3-dimensional space occupied by an object • Temperature - a measure of the warmth or coldness of an object or substance with reference to another value

  3. What are Gas Laws? • Gas Laws study the relationship between these terms • Bed of Nails video

  4. Bed of Nails Video

  5. Pressure • Bed of Nails Video - How does this work? • Newspaper/Ruler Demo - How does this work? • How do does pressure play a role in skating on thin ice? How would you rescue somebody? • Why does pumping air into a car tire increase pressure?

  6. Pressure • Pressure = force/unit area • Bed of Nails video - 1/3 of 8500 lbs is 2833 lbs • 2833lbs/3 inches = 944 psi (so at every spike it feels like there is 944 pounds on him)

  7. Pressure • Pressure is directly proportional to the number of molecules • If you double the mols, you will double the pressure (car tire) • units are atm(atmospheres), mm Hg(millimeters of Mercury), psi(pounds per square inch), Pa(pascals), and torr(torr)

  8. Volume • Volume = Length X Width X Height • Volume is inversely proportional to pressure • Double the volume and you will have half the pressure • Units are L, mL, cm3 or m3

  9. Temperature • How is temperature different from heat? • Measured in ˚C and converted to Kelvins • Temperature is directly proportional to pressure • Doubling the Temperature will double the pressure

  10. Gas Properties • Gases expand or compress to fill their container, this means that the volume is variable • Gases have very low densities compared to other states of matter

  11. Kinetic Molecular Theory • Based on an Ideal Gas • an Ideal Gas has the following properties: • volume of each particle is essentially zero (perfume) • particles move in constant, straight line motion • no forces between particles • Average Kinetic Energy is proportional to absolute temperature

  12. Kinetic Molecular Theory • Kinetic energy equation is KE = (1/2)mv2

  13. Atmosphere • Composed of 78% nitrogen, 21% oxygen, and <1% other gases • This atmospheric composition allows life to exist on Earth

  14. Greenhouse gases • Mainly caused by CO2 trapping heat from escaping our atmosphere • CO2 is produced from burning fossil fuels, clear cutting forests, as well as many other daily activities.

  15. Ozone • Ozone (O3) blocks UV radiation from the sun • If all the ozone molecules in Earths atmosphere were stacked on earths surface, it would only form a 3 mm thick layer! • CFC’s break down O3 and is causing the ozone layer to disappear

  16. Standard Temperature and Pressure(STP) • STP is used to compare sets of data between gases • STP = 0 C and 1.00 atm • STP = 273.16 K and 760.00 mm Hg • STP = 273.16 K and 101.325 kPa • STP = 273.16 K and 760.0 torr • Molar Volume = 22.4 L

  17. Avogadro’s Principle • equal volumes of different gases under the same conditions have equal numbers of molecules • So 1.2 L of Carbon has the same number of molecules as 1.2 L of Chlorine • as mols increase so does volume • Remember amount is measured in mols and not grams!!!

  18. Gas Activity • I want each group to explain the following according to their situation • What happens to molecules • What happens to pressure • What happens to volume • What happens to temperature

  19. Gas Activity • Draw on the SmartBoard and prepare a short presentation on what happens in your particular situation. Please include all relative information and draw a picture of what is happening • Table 1 - what happens to your balloon as you climb Mt. Everest • Table 2 - what happens to your balloon as you dive to the bottom of a deep sea trench • Table 3 - what happens to your balloon as you travel from the North Pole to the South Pole • Table 4 - what happens to your balloon as you travel around the equator (relatively same elevation, temperature, etc) • Table 5 - what happens to your balloon as you gradually fill it with helium until it explodes • Table 6 - what happens to your balloon as you take your balloon from an area of extremely high pressure and gradually into a vacuum (no pressure)

  20. Boyle’s Law • The pressure - volume relationship

  21. Cartesian Diver • How does this work?

  22. Pop Gun • How does this work?

  23. Boyle’s Law • Imagine a syringe - as you compress the plunger the trapped gas particles collide with the walls more often which results in higher pressure • If you push with a fixed pressure, the volume will decrease until the pressure inside equals the pressure outside • Temperature must be kept constant

  24. Boyle’s Law • Boyle’s Law states that pressure and volume are inversely proportional • PV = k (constant) • More commonly seen as P = 1/V or V = 1/P • P1V1 = P2V2 when T is constant

  25. Sample Problem • The gas in a balloon has a volume of 4L at 100kPa. The balloon is released into the atmosphere, and the gas in it expands to a volume of 8L. What is the pressure on the balloon at the new volume? • What do we know? • V1 = 4L • V2 = 8L • P1 = 100kPa • P2 = ? (unknown)

  26. Sample Problem Cont’ • Use equation P1V1 = P2V2 • Rearrange to solve for unknown P2=P1V1/V2 • Plug in values • P2 = (100)(4)/8 • P2 = 50kPa

  27. Sample Problem • If the pressure of a 2.5 m3 sample of a gas is 1.5 atm, what volume will the gas occupy if the pressure is changed to 7.5 atm • What do we know? • P1 = 1.5 • V1 = 2.5 • P2 = 7.5 • V2 = ?

  28. Sample Problem Cont’ • Use P1V1 = P2V2 • Rearrange equation to solve for what we want V2 = P1V1/P2 • Plug in variables • V2 = (1.5 X 2.5)/7.5 • V2 = .5

  29. Charles's Law • The temperature vs. volume relationship

  30. Egg Demo • How does this work?

  31. Video • Better demo of balloon example

  32. Crunching Can • How does this work?

  33. Charles’s Law • Particles move faster when they are heated • Particles push with more force when they are heated

  34. Charles’s Law • Temperature and Volume are directly proportional, so as temp in/decreases, so does volume.

  35. Absolute Temperature Scale • Measured in Kelvins • Kelvins are just like ˚C or ˚F • 0˚C = 273 K

  36. Kelvin Temperature Scale • Converting ˚C to K = take ˚C temp and add 273 • Converting K to ˚C = take K temp and subtract 273 • 0˚ K is theoretically lowest possible temperature

  37. Charles’s Law • Charles’s Law is Volume/Temperature or V/T • It is also used as V1/T1=V2/T2 when Pressure is constant • It is also used as V1T2=T1V2

  38. Sample Problem • A sample of gas occupies 24 m3 at 100K. What volume would the gas occupy at 400K? • What do we know? • V1 = 24 • T1 = 100 • T2 = 400 • V2 = ?

  39. Sample Problem Cont’ • Charles Law is V1/T1 = V2/T2 • Rearrange it to V2 = (V1)(T2)/T1 • Plug in what you know • V2 = (24)(400)/100 • V2 = 96 m3

  40. Sample Problem • Gas in a balloon occupies 2.5 L at 54˚C at what temperature will the balloon expand to 7.5 L? • What do we know? • V1 = 2.5 • T1 = 54˚C • V2 = 7.5 • T2 = ?

  41. Sample Problem Cont’ • Equation = V1/T1 = V2/T2 • Rearrange = T2 = (T1)(V2)/V1 • Convert 54˚C to K (54 + 273 = 327) • Plug in what you know • T2 = (327)(7.5)/2.5 • T2 = 980 K (980-273) = 707 ˚C

  42. Converting from ˚C to K • Remember K = ˚C + 273 • 37˚C • 2˚C • 150˚C • 84˚C • 534˚C

  43. Converting from K to ˚C • Remember ˚C = K - 273 • 465 K • 273 K • 487 K • 182 K • 65 K

  44. No Name LawThe Pressure - Temperature Relationship • Also known as the Gay-Lussac Law • Gay-Lussac used unpublished info from Charles Law and made the following law: • P1/T1 = P2/T2 • This Law is also used as P1T2 = P2T1 • We will use this law in the lab • Remember temperature must be in Kelvins

  45. Combined Gas Law • The pressure - volume - temperature relationship

  46. Combined Gas Law • Boyles Law + Charles Law + Gay-Lussacs Law = Combined Gas Law

  47. Boyles Law • Boyle’s Law states that pressure and volume are _________ proportional • Boyles Law equation = __________ • (P1)(V1) = (P2)(V2) or P = 1/V and V = 1/P • Temperature is constant

  48. Charles Law • Charles’s Law states that volume and temperature are ________ proportional • Charles Law equation = ______ • (V1)(T2) = (T1)(V2) or V1/T1 = V2/T2 • Pressure is constant

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