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Chapter 11: Molecular Composition of Gases. Sect. 11-1: Volume-Mass Relationships of Gases. Gay-Lussac’s Law of combining volumes of gases – at constant temperature and pressure, the volume of gaseous reactants and products can be expressed as ratios of small whole numbers.
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Sect. 11-1: Volume-Mass Relationships of Gases • Gay-Lussac’s Law of combining volumes of gases – at constant temperature and pressure, the volume of gaseous reactants and products can be expressed as ratios of small whole numbers
Avogadro’s law – equal volumes of gases at the same temperature and pressure contain equal number of molecules • Coefficients in a balanced equation show relative # of molecules, moles, and volumes
Standard molar volume of a gas – the volume occupied by one mole of a gas at STP • Numerically 22.4 L = 1 mol
Ex: A chemical reaction produces 0.0680 mol of oxygen gas. What volume in liters is occupied by this gas sample at STP?
Ex.: A chemical reaction produced 98.0 mL of sulfur dioxide gas at STP. What was the mass (in grams) of the gas produced?
Sect. 11-2: The Ideal Gas Law • Ideal gas law – mathematical relationship between pressure, volume, temperature, and number of moles of gas • Relationships are the same as in other gas laws
PV = nRT • Ideal gas constant – the constant, R, in the ideal gas law • Pg. 342 in textbook • Value depends upon pressure units
Ex: What is the volume, in liters, of 0.250 mol of oxygen gas at 20.0°C and .974 atm pressure?
What mass of chlorine gas, Cl2, in grams, is contained in a 10.0 L tank at 27°C and 3.50 atm of pressure?
Ideal gas law can be rearranged to accommodate mass or density • M = mRT/PV, where M is molar mass and m is mass of sample • D = MP/RT, where M is molar mass and D is density
At 28°C and 0.974 atm, 1.00 L of gas has a mass of 5.16 g. What is the molar mass of this gas?
Sect. 11-4: Effusion and Diffusion • Diffusion – gradual, random mixing of gas particles • Effusion – gas particles escaping from a tiny opening in their container
Graham’s Law of Effusion – the rates of effusion of gases at the same temperature and pressure are inversely proportional to the square roots of their molar masses Rate of A = √Molar Mass B Rate of B √Molar Mass A
Ex: A sample of hydrogen gas effuses about 9 times faster than an unknown gas. What is the molar mass of the unknown gas?