MOLECULAR COMPOSITION OF GASES

Chapter 11

I. Molecular Composition of GasesA. Volume-Mass Relationship of Gases

1. Avogadro’s Lawa. Equal volumes of gas at same temp

and pressure have equal numbers of molecules

b. 1mol = 6.02 x 1023 moleculesc. 1 mol of H2 and 1mol of Cl2 have the same amount of particles

2. Molar volume of gasesa. STP = standard temperature and pressureb. 1 mol of gas at STP = 22.4 L

Examples:1. A chemical reaction produces

0.0680 mol of oxygen gas. What volume in liters is occupied by this gas sample at STP?

2. 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. What was the mass (in grams) of the gas produced?

Moles and liters assignment

B. Ideal Gas Law1. Ideal Gas Law

a. Relationship between pressure, volume, temperature, and # of moles of a gas

b. PV = nRT1) T = temp in kelvin2) R = constant

a) Unit mm Hg = 62.4b) Unit atm = 0.0821c) Unit Pa = 8.314d) Unit kPa = 8.314

3) n = moles2. 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 20.0 C and 0.974 atm pressure?

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 assignmentPractice problems pg 343, 344, 345

3. Finding Molar mass and density from Ideal gas lawa. M = mRT = DRT

PV Pb. D = MP

RTc. Need to be in Kelvind. D = density, M = molar mass

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 Diffusion1. Graham’s Law of Effusion

a. 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