Molecular Composition of Gases Chapter 11

I. Molecular Composition of Gases Volume-Mass Relationship of Gases Avogadro’s Law Equal volumes of gas at same temp and pressure have equal numbers of molecules

b. 1mol = 6.02 x 1023 molecules c. 1 mol of H2 and 1mol of Cl2 have the same amount of particles 2. Molar volume of gases a. STP = standard temperature and pressure b. 1 mol of gas at STP = 22.4 L

Examples: A chemical reaction produces 0.0680 mol of oxygen gas. What volume in liters is occupied by this gas sample at STP? At STP, what is the volume of 7.08 mol of Nitrogen gas?

3. A chemical reaction produced 9 L of sulfur dioxide gas, SO2, at STP 3. A chemical reaction produced 9 L of sulfur dioxide gas, SO2, at STP. What was the mass (in grams) of the gas produced? Moles and liters assignment

B. Ideal Gas Law Ideal Gas Law Relationship between pressure, volume, temperature, and # of moles of a gas PV = nRT T = temp in kelvin R = constant Unit mm Hg = 62.4 Unit atm = 0.0821 Unit Pa = 8.314 Unit kPa = 8.314

3) n = moles 2. Examples a. What is the pressure in atmospheres exerted by a 0.500 mol sample of nitrogen gas in a 10.0L container at 298K? (pg 343)

b. What is the volume in liters of 0. 250 mol of oxygen gas at 20 b. What is the volume in liters of 0.250 mol of oxygen gas at 20.0 C and 0.974 atm pressure?

c. What mass of chlorine gas, Cl2, in grams, is contained in a 10 c. What mass of chlorine gas, Cl2, in grams, is contained in a 10.0 L tank at 27 degrees Celsius and 3.50 atm of pressure? (pg 344) Ideal gas law assignment Practice problems pg 343, 344, 345

3. Finding Molar mass and density from Ideal gas law a 3. Finding Molar mass and density from Ideal gas law a. M = mRT = DRT PV P b. D = MP RT c. Need to be in Kelvin d. D = density, M = molar mass

Example: At 28 C and 0. 974 atm, 1. 00L of gas has a mass of 5. 16g Example: At 28 C and 0.974 atm, 1.00L of gas has a mass of 5.16g. What is the molar mass of this gas? Assignment pg 346

C. Effusion and Diffusion Graham’s Law of Effusion Lighter gases move faster b. c. Diffusion – mixing gas by random motion d. Effusion – confined gas passes through a tiny opening

Pg 354 fig 11-8 Quick lab pg 353 Figure 11-8 demo???

Compare the rates of effusion of hydrogen and oxygen at the same temperature and pressure H2 and O2 Take square root of 32g/mol divided by 2.02g/mol =3.98; H2 diffuses 3.98x faster than O2 Assignment pg 355