ThursdayFebruary 28, 2013

(Dalton’s Law of Partial Pressures and

Avogadro’s Law)

Bell RingerThursday, 2-28-13

What instrument is used to measure atmospheric pressure?A barometer

Show the equation that equates the eight units of standard atmospheric pressure.

760 mmHg= 760 torr= 1 atm= 1.013 25 x 105 Pa = 101.325 kPa= 29.92 in Hg = 1 013.25 millibars= 14.7 psi

Announcements

Happy National Chili Day!

??

AnnouncementsI will not be available

after school today.

Assignment Currently Open

Summative or

Formative?Date

Issued Date Due Date Into GradeSpeed Final Day

QUIZ 19 S4 2/15 2/15 TOMORROW

WS – The Nature of Gases F19 2/20 2/21 TOMORROW

QUIZ 20 S5 2/22 2/22 3/8

TELPAS Writing Sample F1 2/25 3/1 TOMORROW

WS – Gas Pressure and Force F2 2/26 2/28 TOMORROW

WS – Measuring Pressure and Units

of PressureF3 2/27 3/1 3/8

John Dalton, the English chemist who proposed the atomic theory, also studied

gas mixtures.

He found that in the absence of a

chemical reaction, the pressure of a gas mixture is the sum of

the individual pressures of each

gas alone.

Dalton’s Law of Partial Pressures

This picture shows a 1.0 L container filled with oxygen gas

at a pressure of 0.12 atm at 0°C.

In another 1.0 L container, an equal number of molecules of nitrogen gas exert a pressure

of 0.12 atm at 0°C.The gas samples are then

combined in a 1.0 L container. (At 0°C, oxygen gas and

nitrogen gas are unreactive.)The total pressure of the

mixture is found to be 0.24 atm at 0°C.

The pressure that each gas exerts in the mixture is

independent of that exerted by other gases present.

The pressure of each gas in a mixture is called the partial

pressure of that gas.

Dalton’s Law of Partial Pressures

Dalton’s law of partial pressures states that the total pressure of a

mixture of gases is equal to the sum of the partial pressures of the

component gases.The law is true regardless of the

number of different gases that are present.

Dalton’s law may be expressed as follows:

PT = P1 + P2 + P3 + . . .PT is the total pressure of the

mixture. P1, P2 , P3, . . . are the partial pressures of component gases

1, 2, 3, and so on.

Dalton’s Law of Partial Pressures

Sample ProblemThree of the primary components of air are carbon dioxide, nitrogen, and oxygen. In a sample containing a mixture of

only these three gases at exactly one atmosphere pressure, the partial pressures of carbon dioxide (PCO2) = 0.285 torr and nitrogen (PN2) = 593.525 torr. What is the partial pressure of

oxygen?

Dalton’s Law of Partial Pressures

PT = P1 + P2 + P3 + . . .

Pair = P CO2 + P N2 + P O2

Pair = 1 atm = 760.000 torr

760.000 torr = 0.285 torr + 593.525 torr + P O2

P O2 = 760.000 – 0.285 – 593.525 = 166.190 torr

Avogadro’s LawIn 1811, Amedeo Avogadro hypothesized that two given samples of an ideal gas, of the same volume and at the

same temperature and pressure, contain the same number of molecules.

Thus, the number of molecules or atoms in a specific volume of gas is independent of their size or the molar

mass of the gas.

As an example, equal volumes of molecular hydrogen and nitrogen contain the same number of molecules when they are at the same temperature and

pressure, and observe ideal gas behavior.

Avogadro’s LawConsider the reaction of hydrogen and chlorine to produce

hydrogen chloride.According to Avogadro’s law, equal volumes of hydrogen

and chlorine contain the same number of molecules.

H2 + Cl2 → 2HCl1 volume 1 volume 2 volumes

1 molecule 1 molecule 2 molecules

Avogadro’s LawAvogadro’s law also indicates that gas volume is directly proportional to the amount of gas,

at a given temperature and pressure.Note the equation for this relationship.

V = knHere, n is the amount of gas, in moles, and k is

a constant.

WorksheetDalton’s Law (Partial

Pressures)Avogadro’s Law

(Same V,T,&P – Same Number of Molecules)