CHAPTER 10 Study Guide 1. Basic Characteristics of Gases a. Variable shape and volume b. Particles move and zoom around more quickly than liquid and solid particles. c. Larger average distances between them than particles of liquids and solids. d. Constant collisions and experience comparatively little attraction to each other. 2. Pressure a. Conveys the idea of force, a push that tends to move something in a given direction. Pressure, P, is defined in science as the force, F, that acts on a given area, A. P = F/A b. Gases exert a pressure on any surface with which they are in contact. The gas in an inflated balloon, for example, exerts a pressure on the inside surface of the balloon. c. SI unit for pressure is a Pascal (Pa) i. Other common units include atm, mm Hg, torr, psi ii. 1 atm = 760 mm Hg and 760 torr = 14.7 psi d. On earth, all of us experience something called atmospheric pressure. This is called, essentially, the pressure exerted upon our bodies by all the gas molecules above us in the atmosphere. i. At higher altitudes, we experience lower atmospheric pressures because there are fewer molecules ‘on top’ of us. At lower altitudes, we experience higher atmospheric pressures. As we go underwater, we experience the combined pressures of all the water molecules above us, plus all the gas molecules in the atmosphere above them. e. STP: Standard Temperature and Pressure i. P = 1 atm ii. T = 0C or 273.15 K 3. Ideal Gas a. A hypothetical gas whose pressure, volume, and temperature relationships can all be predicted by the ideal gas law. Most gases are ideal gases at some range around STP. Gases begin to behave non-ideally under extreme temperatures, pressures, or volumes. b. One mole of any ideal gas (regardless of molecular weight) at STP has a volume of 22.41 L/mol 4. The Combined Gas Law a. P1V1/T1 = P2V2/T2 5. Ideal Gas Law PV = nRT a. Where P is the gas’ pressure, V is the gas’ volume, n is the number of moles of the gas, R is the ‘ideal gas constant’, and T is the gas’ temperature. b. What is R? Depend on units i. 0.08206 L atm/K mol ii. 8.314 J/K mol 6. Density and Molar Mass of Gases d = (n) (MW) / V = P (MW) / RT a. Where d is the gas density (mass/volume), n = number of moles of the gas, MW is the gas’ molecular weight (g/mol), V is the gas’ volume, P is the gas’ pressure, R is the ideal gas constant, and T is the gas’ temperature. 7. Dalton’s Law of Partial Pressure a. Total pressure of a mixture of gases equals the sum of the pressures that each gas would exert if it were present alone. b. P Total = P1 + P2 + P3 +…. c. Each gas behaves independently of the others hence, can calculate each gas’ individual pressure by using the ideal gas law equation like this… P1 = n1(RT/V); P2 = n2(RT/V) …… 8. Partial Pressures and Mole Fractions a. Partial pressures are directly proportional to mole fractions of gases in a mixture b. Therefore, if you have three gases (X, Y, and Z) then their individual pressures are proportional to their individual molar percentages. 9. Dalton’s Law of Partial Pressure a. Total pressure of a mixture of gases equals the sum of the pressures that each gas would exert if it were present alone. b. P Total = P1 + P2 + P3 +…. c. Each gas behaves independently of the others hence, can calculate each gas’ individual pressure by using the ideal gas law equation like this… P1 = n1(RT/V); P2 = n2(RT/V) ……

Basic Characteristics of Gases Study Guide

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