Ch. 5 Gases!!!!!

Pressure conversionsO Pressure – force per unit areaO Can be measured in atm, mmHg, torr,

kPa, psiO 1atm =760mmHg = 760torr =

101.3kPa= 14.7psiO Measured with a barometer

(atmospheric pressure) or a manometer (pressure within a container)

Main variables with gases

O Pressure (P)O Volume (V)O Temperature (T)O Moles (n)O Ideal gas constant (R) = 0.08206

Boyles, Charles, Gay Lussac, Combined, Avogadros

O Boyles: P1V1 = P2V2

O Charles: V1/ T1 = V2 / T2

O Gay Lussac: P1 / T1 = P2 / T2

O Combined: P1V1 = P2V2

T1 T2

O Avogadro: V1/n1 = V2/n2

Sample Questions1. A balloon is filled to a volume of

7.00 x 102mL at a temperature of 20.0°C. The balloon is then cooled at constant pressure to a temperature of 1.00 x 102K. What is the final volume of the balloon?

Sample Questions

2. An 11.2-L sample of gas is determined to contain 0.50 mol N2. At the same temperature and pressure, how many moles of gas would there be in a 20.0L sample?

Sample Questions

3. Suppose two 200.0L tanks are to be filled separately with the gases helium and hydrogen. What mass of each gas is needed to produce a pressure of 135 atm in its respective tank at 24°C?

Ideal Gas LawO PV = nRTO What units do each of the variables

have to be in for this law?O Sample Question: A 5.0L flask

contains 0.60g of O2 at a temperature of 22°C. What is the pressure (in atm) inside the flask?

Gas StoichiometryO 1 mole of ANY gas at STP = 22.4LO 22.4L is the “molar volume” of an

ideal gasO Use this conversion to skip using the

ideal gas law O Sample problem: A sample of

nitrogen gas has a volume of 1.75L at STP. How many moles are present?

Molar Mass of a Gas

O Molar mass = dRT P

O d = density (g/L)O R = ideal gas constantO T = temperatureO P = pressureO Sample: The density of a gas was measure at

1.50atm and 27°C and found to be 1.95g/L. Calculate the molar mass of the gas.

Dalton’s Law of Partial PressuresO Ptotal = P1 + P2 + P3

…

O P1, P2 and P3 are called partial pressures

O Ptotal can also be calculated if you know the total number of moles (ntotal)

O Ptotal = ntotal(RT/V)

O Mole fraction is also important to thisO Mole fraction (χ1) = n1/ntotal

O Mole fraction is directly related to partial pressure: χ1 = n1/ntotal = P1/Ptotal

Dalton’s Law Sample Question

1. The partial pressure of oxygen was observed to be 156 torr in air with a total atmospheric pressure of 743 torr. Calculate the mole fraction of O2 present.

Another Sample Question

1. Mixtures of He and O2 can be used in scuba diving tanks to help prevent the “bends.” For a particular dive, 46L He at 25°C and 1.0atm and 12L O2 at 25°C and 1.0atm were pumped into a tank with a volume of 5.0L. Calculate the partial pressure of each gas and the total pressure in the tank at 25°C.