Chemistry IIUnit 1 Gases

Ideal GasesObjectives1. Compute the value of an unknown using the

ideal gas law.2. Compare and contrast real and ideal gases.

Avogadro’s Principle and Molar VolumeAvogadro’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.

Avogadro’s Law

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

2. How many grams of carbon dioxide, CO2, will occupy a volume of 500.0 mL at STP?

V= 500.0mL =0.5 LMolar mass CO2= 44g/molAt STP, molar volume is : 22.4L/1 mol

Classwork: p 132 # 1 (a,b), 2(b,c), 3 (b,c)

The ideal gas lawConsiders 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 KR= 0.0821 L atm (when pressure is

measured in atm)mol K

Ideal gas law: PV= nRT (T must be in Kelvin)

Using the ideal gas law1. 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?

Using the ideal gas law2. How many moles of oxygen will occupy a

volume of 2.5 L at 1.2 atm and 25C? (0.123 moles)

Classwork: p 133 # 7,8 and p141 # 3,4

Ideal gas variationsFor calculating molar mass

M= mRT M: molar mass (g/mol) PV m: mass (g)

For calculating densityD= MP D: density (g/L) RT

Sample problem1. What is the molar mass of sulfur dioxide,

SO2, if 300 mL of the gas has a mass of 0.855 g at STP?

2. At what temperature will 5.00g of Cl2 exert a pressure of 115 kPa at a volume of 750 mL?

3. If the density of a gas is 1.2 g/L at 0.920 atm and 20C, what is its molar mass?

Classwork: p 133 #5,6, 9 and p141 #2,5