CHAPTER 11: THE GASEOUS STATE

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1 CHAPTER 11: THE GASEOUS STATE DO Problems: 1-2, 3b, 4a, 5a, 6b, 7, 8a, 9-14, 17-20, 23-26, Properties of Gases 1. Gases have indefinite shape take the shape of its container 2. Gases can expand or compress If the volume is increased, the gas expands to fill the larger volume. If the volume is decreased, the gas particles move closer together. 3. Gases have low densities About 1000 times less dense than liquids and solids Why density of gases reported in g/l 4. Gases will mix in their containers to form uniform mixtures 5. A gas confined to a container will exert pressure on the container walls since the particles are constantly in motion Atmospheric Pressure gas pressure: force per unit area exerted by gas molecules colliding against the inside of its container a measure of how often molecules hit container walls Evangelista Torricelli published the first explanation for a vacuum in 1600 s. Ancient Greeks observed that wine barrel empties slowly if only one hole is drilled Torricelli explained that a sea of air surrounding the Earth slows the flow of wine out of the barrel If you create a second hole on the top of the barrel, air molecules can rush in and push the liquid out, so it flows faster vacuum: no gas molecules present, so gas pressure equals zero atmospheric pressure: pressure exerted by air molecules colliding with surfaces in environment anything entering earth's atmosphere burns up! decreases as altitude increases because air becomes thinner About 760 torr at sea level, lower at higher altitudes like Denver Corwin Chapter 11 page 1 of 5

2 barometer: instrument invented by Torricelli to measure atmospheric pressure standard atmospheric pressure: a column of mercury measuring 760 mm Hg. 1 atm 760 torr 760 mm Hg = 14.7 psi (approx.) Ex. 1: The tire pressure for tires used on most automobiles is about 32 psi. Express this pressure in atm, torr, and mmhg Variables Affecting Gas Pressure What happens to the pressure of a gas given the following changes? (Circle one for each below.) a. If Volume, pressure. stays same Thus, pressure and volume are related. not directly inversely b. Temperature, pressure. stays same Thus, pressure and temperature are related. not directly inversely c. # of gas molecules, pressure. stays same Thus, pressure and # of molecules are related. not directly inversely Corwin Chapter 11 page 2 of 5

3 11.7 Combined Gas Law Consider when there are changes in P,V, and T for a gas Boyle's Law: Pressure-Volume Changes When T is constant, but V and P of the gas are changed Charles' Law: Volume-Temperature Changes When P is constant, but V and T (in Kelvins) are changed Gay Lussac's Law: Pressure-Temperature Changes When V is constant, but P and T (in Kelvins) are changed. Corwin Chapter 11 page 3 of 5

4 Guidelines for solving gas law problems: 1. List all of the measurements given, and label each as P 1, V 1, T 1, etc. " 2. Starting with the Combined Gas Law P 1V 1 = P % 2V 2 $ # T 1 T ', cancel variables that 2 & remain constant. 3. Isolate the unknown variable. 4. Convert all temperatures to Kelvins, convert all pressures to the same units, convert all volumes to the same units. 5. Solve for the unknown, making sure your final answer has the correct units and the correct number of sig figs. 6. Check if your final answer makes sense. Exercises: If a value (P, V, or T) is not given, that value remains constant. 1. A mL sample of CO gas at 1.20 atm is compressed to ml. Calculate the new pressure. 2. If 25.0 ml of hydrogen gas are heated from 225K to 675K, calculate the new volume. Corwin Chapter 11 page 4 of 5

5 3. A sample of CO 2 gas at 2.50 atm is cooled from 75 C to 25 C. Calculate the new pressure. 4. A 5.00 L sample of neon gas at 25 C and atm is heated to 325K. If the new volume of the gas is 10.0 L, calculate the new pressure for the gas. 5. A sample of krypton gas at -85 C and 955 torr occupies 50.5 ml. What is the volume at standard temperature and pressure, STP. At STP, the temperature = and the pressure =. Know standard temperature and pressure, STP (1.00 atm and 0 C)! Corwin Chapter 11 page 5 of 5