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?