GASES Chemistry I – Chapter 14 Chemistry I Honors – Chapter 13 - PowerPoint PPT Presentation

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GASES Chemistry I – Chapter 14 Chemistry I Honors – Chapter 13

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  1. GASESChemistry I – Chapter 14Chemistry I Honors – Chapter 13 SAVE PAPER AND INK!!! When you print out the notes on PowerPoint, print "Handouts" instead of "Slides" in the print setup. Also, turn off the backgrounds (Tools>Options>Print>UNcheck "Background Printing")!

  2. GAS: One of Three STATES OF MATTER

  3. General Properties of Gases • There is a lot of “free” space in a gas. • Gases can be expanded infinitely. • Gases fill containers uniformly and completely. • Gases diffuse and mix rapidly.

  4. Importance of Gases • Airbags fill with N2 gas in an accident. • Gas is generated by the decomposition of sodium azide, NaN3. • 2 NaN3 ---> 2 Na + 3 N2

  5. Our Atmosphere: Gravity holds the atmosphere close to the Earth. It is divided into various layers according to differences in temperature: • The Troposphere: • We live in the Troposphere • It contains more than 75% of the atmosphere’s mass • The Stratosphere: • Most of the clouds and rain are in this layer • It extends up to 48km above the earth! • The ozone layer is between the Stratosphere and Mesosphere • The Mesosphere: • This layer extends to 80km above the Earth! • The Thermosphere • Here the air is very thin • Over 99.99% of the atmosphere lies below this layer • It is comprised of:

  6. http://library.thinkquest.org/C003124/en/atmos.htm

  7. The Ionosphere:Reflects radiowaves back to Earth so signals can be sent around the world • The Exosphere:This layer begins at ~480km above the Earth and fades away into space

  8. Did you know... • About 99% of the atmosphere is made up of oxygen (21%) and nitrogen (78%). • The remainder is made up of Ar (argon), CO2and very small amounts of H2, NH3, O3(ozone), CH4, CO, He, Ne, Kr and Xe. also gases such as SO2, NO2 are put into the air from vehicles & industry • About 20 % of the Earth's population breathes severely contaminated air, largely CO2 and SO2 resulting from industrial processes. This increases the number of respiratory conditions, especially amongst children and elders. 13 % of the British children experience asthma caused by air contamination

  9. Properties of Gases Gas properties can be modeled using math. Model depends on— • V = volume of the gas (L) • T = temperature (K) • ALL temperatures in the entire chapter MUST be in Kelvin!!! No Exceptions! • n = amount (moles) • P = pressure (atmospheres)

  10. Temperature • Average kinetic energy of the particles of a substance • Without particles there is no temperature • No temperature in a vacuum • Must be measured in Kelvin to avoid negative values while doing calculations C° + 273 = K

  11. PRESSURE: A FORCE per unit area • Measured in pascals (Pa) = 1 N/m2 = 100 g / m2 • A normal day has a pressure of 100 kPa = 100 x 1000 Pa x 100 g / m2 1 kPa = 10 000 kg / m2 Atmospheric pressure varies with altitude • the lower the altitude, the longer and heavier is the column of air above an area of the earth.

  12. Pressure Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643) Hg rises in tube until force of Hg (down) balances the force of atmosphere (pushing up). (Just like a straw in a soft drink) P of Hg pushing down related to • Hg density • column height

  13. Pressure Column height measures Pressure of atmosphere • * 1 standard atmosphere (atm) = 760 mm Hg (or torr) = 29.92 inches Hg = 14.7 pounds/in2 (psi) = * 101.3 kPa (SI unit is PASCAL) = about 34 feet of water! * Memorize these!

  14. Pressure Conversions • The air pressure in a cave underwater is 2.30 atm, what is the pressure in kPa? 101.3 kPa B. What is 475 mm Hg expressed in kPa? 101.3 kPa 760 mm Hg 2.30 atm x = 233 kPa 1 atm 475 mm Hg x = 63.31 kPa

  15. Pressure Conversions • The air pressure in a cave underwater is 2.30 atm, what is the pressure in kPa? 101.3 kPa B. What is 475 mm Hg expressed in kPa? 101.3 kPa 760 mm Hg 2.30 atm x = 233 kPa 1 atm 475 mm Hg x = 63.31 kPa

  16. Pressure Conversions A. What is 3.71 atm expressed in kPa? B. The pressure of a tire is measured as 830 torr. What is this pressure in atm?

  17. Crushed Can Demo: Why did the can implode? What happened to the pressure inside once the temperature decreased? Lower temperature = slower moving particles = less collisions with the wall T P Did the # of particles/moles change? Did the air pressure change(# particles colliding)? Did the volume change? Only because the pressure outside is much greater then inside – the ouside pressure crushed the can. http://phet.colorado.edu/en/simulation/gas-properties T α P

  18. Gay-Lussac’s Law If n and V are constant, then P α T P and T are directly proportional. P1 P2 = T1 T2 • If temperature goes up, the pressure goes up! P1=T1 P2 T2 Joseph Louis Gay-Lussac (1778-1850) Charles’ Law http://www.youtube.com/watch?v=tPH57yp0x1U

  19. Gas Pressure, Temperature, and Kinetic Molecular Theory As the temperature increases the particles move faster  increasing # of collisions = ↑ pressure P proportional to T

  20. A gas has a pressure of 3.0 atm at 127º C. What is its pressure at 227º C? T1 = 127°C + 273 = 400K P1 = 3.0 atm T2 = 327°C + 273 = 600K P2 = ? What law applies to this situation? T and P – Gay-Lussac’s Law: 3.0 atm=P2P2= 3.0 atm x 600 K P2 = 4.50 atm 400K 600K 400 K P1=P2 T1 T2

  21. Charles’s Law If n and P are constant, then V α T V and T are directly proportional. V1 V2 = T1 T2 • If temperature goes up, the volume goes up! V1=T1 V2 T2 Jacques Charles (1746-1823). Isolated boron and studied gases. Balloonist.

  22. Charles’s original balloon Modern long-distance balloon

  23. Charles’s Law 0 K-273 °C Boyle’s Law – Vacuum Demo - http://www.youtube.com/watch?v=N5xft2fIqQU

  24. A gas has a volume of 3.0 L at 127°C. What is its volume at 227 °C? T1 = 127°C + 273 = 400K V1 = 3.0 L T2 = 227°C + 273 = 500K V2 = ? Which law applies to this situation? T and V - Charles’s Law: 3.0 L = V2V2 = 3.0 L x 500 K V2 = 3.75 L 400 K 500 K 400 K V1=V2 T1 T2

  25. Boyle’s Law P α 1/V This means Pressure and Volume are INVERSELY PROPORTIONAL if moles and temperature are constant (do not change). For example, P goes up as V goes down. P1V1 = P2 V2 Robert Boyle (1627-1691). Son of Earl of Cork, Ireland.

  26. As Pressure Increases Volume decreases

  27. Boyle’s Law and Kinetic Molecular Theory P proportional to 1/V Smaller volume means the particles are forced closer together – increasing collisions with each other and with the walls of the container.

  28. Boyle’s Law A bicycle pump is a good example of Boyle’s law. As the volume of the air trapped in the pump is reduced, its pressure goes up, and air is forced into the tire.

  29. Volume Pressure Boyle’s Law: - PV = k Temperature is constant

  30. A gas has a volume of 3.0 L at 2 atm. What is its volume at 4 atm? P1 = 2 atm V1 = 3.0 L P2 = 4 atm V2 = ? Which law applies to this situation? P and V = Boyle’s Law 2 atm x 3.0 L = 4 atm x V2 V2 = 2 atm x 3.0 L 4 atm V2 =1.5 L P1 V1 = P2 V2

  31. SUMMARY of Gas Laws

  32. Combined Gas Law • The good news is that you don’t have to remember all three gas laws! Since they are all related to each other, we can combine them into a single equation. BE SURE YOU KNOW THIS EQUATION! V1 P1 V2 P2 = T1 T2

  33. Combined Gas Law If you only need one of the gas laws, you can cover up the item that is constant and you will get that gas law! = P1 V1 P2 Boyle’s Law Charles’ Law Gay-Lussac’s Law V2 T1 T2

  34. Combined Gas Law Problem A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm? Given: P1 = 0.800 atm V1 = 180 mL T1 = 29°C + 273 = 302 K P2 = 3.20 atm V2= 90 mL T2 = ??

  35. Calculation P1 = 0.800 atm V1 = 180 mL T1 = 302 K P2 = 3.20 atm V2= 90 mL T2 = ?? P1 V1 P2 V2 = P1 V1T2 = P2 V2 T1 T1T2 T2 = P2 V2 T1 P1 V1 T2 = 3.20 atm x 90.0 mL x 302 K 0.800 atm x 180.0 mL T2 = 604 K - 273 = 331 °C = 604 K

  36. Learning Check A gas has a volume of 675 mL at 35°C and 0.850 atm pressure. What is the temperature in °C when the gas has a volume of 0.315 L and a pressure of 802 mm Hg?

  37. One More Practice Problem A balloon has a volume of 785 mL on a fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon?

  38. And now, we pause for this commercial message from STP STP in chemistry stands for Standard Temperature and Pressure STP allows us to compare amounts of gases between different pressures and temperatures Standard Pressure = 1 atm (or an equivalent) Standard Temperature = 0 deg C (273 K)

  39. Try This One A sample of neon gas used in a neon sign has a volume of 15 L at STP. What is the volume (L) of the neon gas at 2.0 atm and –25°C?

  40. Ideal Gases, Avogadro’s Theory and the Ideal Gas Law What are three things that make the behaviour of a gas ideal? • How do they collide? 2) Does their size matter? 3) How do they move?

  41. What are three things that make the behaviour of a gas ideal? • How do they collide? ELASTICALLY  no attraction, no energy loss, perfect bounces 2) Does their size matter? NO too small, spaces between too big 3) How do they move? straight lines and randomly

  42. FYI: What you will see in university

  43. twice as many molecules Avogadro’s Theory Equal volumes of gases at the same T and P have the same number ofmolecules. • Volume is proportional to moles • V and n are directly related • V α n twice the volume

  44. Ideal Gas Law: Generally speaking, an ideal gas obeys all gas laws perfectly under all conditions: 1) Charles’s Law V α T (V / T = k ) 2) Gay-Lussac’s Law P α T (P / T = k ) 3) Boyle’s Law V α 1 / p ( V x P = k ) 4) Avogadro’s Theory V α n In other words, V α n α T α 1/p All these variables can be combined to include an equation with moles, n using a constant… V = constant x n x T x 1/p The constant is the letter R

  45. Ideal Gas Law: The Constant R: • Is called the Ideal GAS CONSTANT • Relates P, T, V, and moles • Is found by substituting in known values for P, T, V and n (moles) Ex. You could sub in values at STP: T = 273 K, P = 1 atm, 1 molegas= 22.4 L R with different units : These #’s are always provided . • 8.314 J / K • mol or 8.314 J K-1 mol-1 • 0.0821 L•atm/K•mol mainly used • 8.31451 Pa m3 K-1 mol-1 • 62.364 L Torr K-1 mol-1

  46. IDEAL GAS LAW V= R x n x T x 1/p Multiply both sides by p, rearrange n… Brings together gas properties. Can be derived from experiment and theory. BE SURE YOU KNOW THIS EQUATION! P V = n R T http://jersey.uoregon.edu/vlab/Piston/index.html

  47. Using PV = nRT P = Pressure V = Volume T = Temperature N = number of moles R is the constant called the Ideal Gas Constant R = 0.0821 L • atm Mol • K