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Chapter 5: What we have learned so far

Chapter 5: What we have learned so far. Know that 1m 3 = 1000L (metric volume conversions in general) n = mass/molar mass Kelvin = o C + 273.15 (All calculations must be in Kelvins for this chapter) All the pressure conversions …

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Chapter 5: What we have learned so far

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  1. Chapter 5: What we have learned so far

  2. Know that 1m3 = 1000L (metric volume conversions in general) n = mass/molar mass Kelvin = oC + 273.15 (All calculations must be in Kelvins for this chapter) All the pressure conversions … 1.013 bar = 1 atm = 760 mm Hg = 14.7 PSI = 100 kPa = 760 torr HW #51 Section 5.1- Measurements on Gases

  3. PV = nRT(Ideal Gas Law) Ideal gas law can be reduced down to 4 other equations … Boyle’s Law – P1V1=P2V2 (when n and T are constant) Pressure and Volume inversely proportional Charles Law – V1/T1 = V2/T2 (when n and P are constant) Volume and Temperature are directly proportional Gay-Lussac’s Law – P1/T1 = P2/T2 (when n and V are constant) Pressure and Temperature are directly proportional Combined Gas Law - P1V1/T1=P2V2/T2 (when n is constant) Section 5.2 – Ideal gas law

  4. Standard PV=nRT problems • Initial and Final State Problems (Can set ideal gas law equal to itself and cancel terms or use the four gas law equations) • Problems where you determine the molar mass or density of a gas (remembering n=m/MM and m/V) • HW#52 Section 5.3 – Gas Law Calculations

  5. STP conditions (0oC and 1 atm) • At STP conditions: a mole of any gas equals 22.4L • Gay-Lussac in 1808 … “The volume ratio of any two gases in a reaction at constant temperature and pressure is the same as the reacting mole ratio” • 1CH4(g) + 2O2(g) 1CO2(g) + 2H2O(g) • This means 1 molecule of methane gives 2 molecules of water • This means 1 mole of methane gives 2 moles of water • And now, 1 liter of methane gives 2 liters of water (as long as they are gases) • HW#53 Section 5.4 – Gas Law and Stoich Problems

  6. Chapter 5: What is Left to Learn

  7. Dalton’s Law of Partial Pressures (Ptot = PA + PB + PC …) • A problem related to this is the wet gases problem, collecting gases by water displacement. You usually need to subtract vapor pressure of water to get pressure of collected gas. • Mole Fraction • PA = XAPtotderived from relationship = XA • Therefore the partial pressure of a gas in a mixture is equal to its mole fraction multiplied by the total pressure • HW#54 Section 5.5 – Gas Mixtures

  8. Assumptions of Kinetic Theory • Physics expression for pressure … P • N = number of molecules • m = mass • u = average speed of molecule • V = volume • - Leads to other equations …. • HW#54 Section 5.6 – Kinetic Theory of Gases

  9. - Average Kinetic Energy of Translational Motion • Etwriting in terms of ideal gas law Et • NA = Avogadro’s number 6.02 x 1023 • m = mass • u = average speed of molecule • Average Speed of Molecule • u = 1/2 = 1/2 • HW#54 Section 5.6 – Kinetic Theory of Gases

  10. Graham’s Law: Effusion of Gases • Graham’s Law States …. • “At a given temperature and pressure, the rate of effusion of a gas, in moles per unit time, is inversely proportional to the square root of its molar mass.” • = ½ (constant P and T) • -Don’t worry about “Distribution of Molecular Speeds” • HW#54 Section 5.6 – Kinetic Theory of Gases

  11. Know at what conditions real gases deviate from ideal gas behavior. High Pressure Low Temperature Gas molecule has Polarity (internal charge) All of these conditions tend to move a gas towards a liquid state, so the closer a gas is to liquid, the more it will deviate from ideal behavior (i.e. ideal gas law no longer applies) HW#54 Section 5.7 – Real Gases

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