lesson7-1The KineticTheory of gases


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lesson7-1The KineticTheory of gases

  1. 1. Lesson 7-1 The Kinetic Theory of Gases The Kinetic Theory of Gases is one of the most interesting topics in Chemistry.If you come to truly understand the concepts in this chapter, it will change theway you look at the world around you. One of the great things about this topicis that it explains some of the phenomena that you encounter in your everydaylife. For example, have you ever inflated a pool float until it was firm, thrown itinto a cold pool, and then wondered why the float then seemed like it was notfully inflated? Do you know why a basketball seems flat after it has spent thenight in a cold garage? What determines the time it takes to smell the perfumeof a woman who walks past you? How do hot air balloons work? How can a
  2. 2. small barbeque tank hold enough propane to cook with all summer long? All of these questions can be answered by someone who has studied this chapter. Gases have special properties that liquids and solids dont have. The molecules that make up the gas are free to move about, and a gas will take up the size and shape of its container. Knowing the volume of a gas tells you very little about the quantity of matter, because any sample of gas will fill its container. If you have a ten-gallon tank on your barbeque, it is always technically full! In order to have an idea of the amount of matter that a sample of gas represents, you need to know the temperature and the pressure of the gas. Ideal Gases - Consider how different a gas is from a solid. In a gas, the size of the sample has very little to do with the size of the actual atoms that make up the gas itself. Even in relatively dense gas samples, the space in between the molecules will be much larger than the molecules themselves. When we do math problems involving gases, we treat the particles as point masses, or particle with mass but no volume. Ideal gases differ from real gases in another important way. In real gases, there will be an attraction between the particles involved. These attractions are often minor and we ignore them when we do math problems involving gases. It is important to remember the differences between real gases and ideal gases. It is also interesting to note that real gases will act most like ideal gases at low pressure and high temperature, when the gas sample is less dense. Pressure - You may recall that pressure is defined as a force over an area. InChemistry, pressure is often measured in kilopascals (kPa), millimeters of mercury(mm of Hg), or atmospheres (atm). For convenience sake, a standard atmosphericpressure has been set at 101.3 kPa, which is also equal to 760 mm of Hg and 1.0atm. As a student of Chemistry you should be aware of the following constants andconversions: Standard Atmospherice Pressure = 101.3 kPa = 760 mm of Hg = 1.0 atm 1 kPa = 7.50 mm of Hg Temperature - Many of the thermometers that are used in Chemistry laboratoriesare marked with the Celsius scale. However, when we do math problems involvingthe temperature, volume and pressure of gases, we must use the Kelvin scale. Thereason for this is the fact that it is possible to have negative numbers on the Celsiusscale, and that would cause problems when measuring the volume of a gas at lowtemperatures. In order to do any gas law calculations involving temperatures, youmust first convert the temperature to Kelvin. As a reminder, the conversionsbetween Kelvin and Celsius are shown below. Co + 273 = K
  3. 3. K - 273 = Co For convenience, standard temperature has been set at 273 Kelvin, which isequal to 0oC. Standard temperature and pressure is abbreviated as STP.Conditions will vary from laboratory to laboratory and from day to day. You willoften be called upon to adjust the volume of the gas that you collected in your ownlab to STP, meaning standard conditions for pressure and temperature. Rememberthe information below. STP = 101.3 kPa and 273 K (or any equivalent values, i.e. 1 atm and 0oC) Kinetic Theory of Gases Quizzes Kinetic Theory of Gases WorksheetsPlease forward all questions, comments and criticisms to Gregory L. Curran.� Copyright 2004 Fordham Preparatory School, All Rights Reserved.Last Modified February 07, 2008