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## Friday 4/27

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**An Introduction to Gases**Chapter 13**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**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.**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.**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 = 101.325 kPa 1 atm = 14.7 psi**Pressure**Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643)**Pressure Calculation**What is 475 mm Hg expressed in atm? 475 mm Hg 1 atm = 0.625 atm 760 mm Hg**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**100 ˚C**373 K 100 K 100˚C 0 ˚C 273 K Temperature Scales Celsius Kelvin Boiling point of water Freezing point of water Notice that 1 kelvin = 1 degree Celsius**Calculations Using Temperature**ALL gas calculations require temperature in Kelvin T (K) = T(˚C) + 273.15 Body temp = 37 ˚C + 273 = 310 K Liquid nitrogen = -196 ˚C + 273 = 77 K**Relationships**How are temperature and volume related? How are volume and pressure related? How are pressure and temperature related?**Reminders**Homework: Gases WS 1 Reminders: Extra Credit Due 5/11 Test Corrections due 5/1**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?**Demo**Now flip the can over into cold water. Predict what do you predict will happen? Put a few drops of water in a can. Heat the can until the water boils. What is happening to the gas inside?**Gas Laws Calculations**Get out a calculator!!!**The Gas Law**PV=nRT P = pressure ( atm or kPa ) V= volume ( L ) n= number of moles (mol) T= temperature (K)**R – The Proportionality Constant**Value depends on units Or**The Gas Law – Problem**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 = 1454.95 kPa P = 1500 kPa**The Gas Law – Problem**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 9.95 atm**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?**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?**Combined Gas Law – Problemc**If we know that R1 = R2 and the mass is constant then Replace with numbers**Combined Gas Law – Problem**P2 = 35 atm**Pressure & Volume**• At constant Temperature • Pressure and Volume vary inversely. • Why? • More collisions More pressure P1V1 = P2V2**P & V – Example Problem**If you start with 0.500 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) 1.0 atm = P2**Temperature & Volume**At constant Pressure Volume & Temperature vary directly. • Why? • More collisions More Volume**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?**S.T.P.**• Standard Temperature and Pressure These are conditions that are universal Standard Temperature: 0ºC or 273.15 K Standard Pressure: 1atm or 101.325kPa**S.T.P. – Example Problem**What is the volume of 1 mole of a gas at STP? PV = nRT (1atm)V = (1 mole)(0.0821 [Latm/Kmole])(273K) V= 22.4 L**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?**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?**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.**Quiz Time**Have out a pencil and a calculator**Cage of Death Lab**• Determine the volume of one mole of gas at STP • Do prelab before class • Lab write up due**Reminders**Homework: Gases WS 2 Cage of Death Pre-lab Reminders: Extra Credit Due 5/11**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?**Cage of Death Lab**• Determine the volume of one mole of gas at STP Gas collection tube Balancing pressure Making cage**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**Cage of Death Lab**4. Why is it important that the HCl and H2O don’t mix? 5. Not too tight Not too loose**Cage of Death Lab**6. (F) Today’s atmospheric pressure is… 8.**Cage of Death Lab**9. Allow reaction to happen… How would a bubble effect your results? 10. Just right Too high Too low**Cage of Death Lab**Repeat the lab for a second trial. CLEAN UP Liquids down drain Solids return to container**After Lab**Done in lab? Work on Homework: Cage of Death Write Up Gases WS 3 Reminders: Extra Credit due 5/11**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?