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Chemistry II

Chemistry II . Unit 1 Gases. Ideal Gases. Objectives Compute the value of an unknown using the ideal gas law. Compare and contrast real and ideal gases. Avogadro’s Principle and Molar Volume

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Chemistry II

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  1. Chemistry II Unit 1 Gases

  2. Ideal Gases • Objectives • Compute the value of an unknown using the ideal gas law. • Compare and contrast real and ideal gases.

  3. Avogadro’s Principle and Molar Volume • Avogadro’s principle states that equal volume of all gases, measured under the same conditions of pressure and temperature, contain the same number of particles. • At STP, the volume of one mole of gas is 22.4 L(this is called the molar volume) • 1dm3 = 1 L; 1L= 1000mL ; 1mL= 1cm3 • From last year, to convert between grams and moles of a substance we used its molar mass.

  4. Avogadro’s Law

  5. Converting between moles and grams: How many moles are 98.32g CO2? Calculate molar mass CO2 (use periodic table) Molar mass= 12 + (2 x 16) =44.0 g/1 mol To convert grams to moles: 98.32g x 1 mol = 2.23 mol CO2 44g

  6. 2. How many grams of carbon dioxide, CO2, will occupy a volume of 500.0 mL at STP? V= 500.0mL =0.5 L Molar mass CO2= 44g/mol At STP, molar volume is : 22.4L/1 mol Classwork: p 132 # 1 (a,b), 2(b,c), 3 (b,c)

  7. The ideal gas law • Considers that amount of gas varies. • New variable • n: number of moles of gas (mol) • Ideal gas constant (R) • R= 8.314 L kPa (when pressure is measured in kPa) mol K • R= 0.0821 L atm (when pressure is measured in atm) mol K • Ideal gas law: PV= nRT(T must be in Kelvin)

  8. Using the ideal gas law • A deep underground cavern contains 2.24x106 L of methane gas (CH4) at a pressure of 1500 kPa and a temperature of 315K. How many moles of CH4 does the cavern contain?

  9. Using the ideal gas law 2. How many moles of oxygen will occupy a volume of 2.5 L at 1.2 atm and 25C? (0.123 moles) Classwork: p 133 # 7,8 and p141 # 3,4

  10. Ideal gas variations • For calculating molar mass • M= mRT M: molar mass (g/mol) PV m: mass (g) • For calculating density • D= MP D: density (g/L) RT

  11. Sample problem • What is the molar mass of sulfur dioxide, SO2, if 300 mL of the gas has a mass of 0.855 g at STP?

  12. At what temperature will 5.00g of Cl2 exert a pressure of 115 kPa at a volume of 750 mL? • If the density of a gas is 1.2 g/L at 0.920 atm and 20C, what is its molar mass? Classwork: p 133 #5,6, 9 and p141 #2,5

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