Gases

A fine presentation by:Mr. Anderson + Mr. Smith

Symbols and Constants

• P = Pressure (Atmospheres)• V = Volume • T = Temperature (Kelvin)• n = Moles• R = 0.0821• STP – Standard temperature and

Pressure, 1 atm and 273 Kelvin

Gas Laws

• Boyle’s Law – P1V1 = P2V2

• Charles’ Law – V1/T1 = V2/T2

• Gay-Lussac’s Law – P1/T2 = P2T2

• Avagadro’s Law – V1/n1 = V2/n2

• Combined Gas Law – P1V1/T1 = P2V2/T2

• The Ideal Gas Law – PV = nRT

Sample Problem

• The pressure of the gas in a 12 liter container is 3.0 atm. If the volume is expanded to a 20 liter container, what is the pressure?

• A. 1.0 atm• B. 1.8 atm• C. 2.0 atm• D 2.2 atm

Another Sample Problem

• 2.5 grams of Mg(s) (Molar Mass = 24.3g) is added to an excess of HCl(aq) and H2(g) is produced. What volume of gas is produced at STP?

• A. 1.5 liters• B. 2.0 liters• C. 2.3 liters• D. 2.5 liters

Effusion

• Effusion – The movement of gas into a vacuum through a small hole

• Graham’s Law – Rate1Rate2 = the square root of MM2/MM1

• We use Graham’s law to calculate how quickly a gas diffuses.

A Sample Problem

• The effusion rate of an unknown gas is measured and found to be 31.50 mL/min. Under identical experimental conditions, the effusion rate of O2 is found to be 30.50 mL/min. What is the identity of the mystery gas?

• A. CH4

• B. CO• C. CO2

• D. NO• E. NO2

Do The AP problem!