Mr. ShieldsMr. Shields Regents Chemistry Regents Chemistry U05 L09 U05 L09

John Dalton (1766 – 1844)John Dalton (1766 – 1844)

- Developed the Law of Partial Pressures (abt. 1801)Developed the Law of Partial Pressures (abt. 1801)

Partial PressuresPartial Pressures

The PRESSURE created by the collision of one gas The PRESSURE created by the collision of one gas in a in a mixture of gases is called the mixture of gases is called the Partial PressurePartial Pressure of of the gasthe gas

Dalton said that molecules of different gasesDalton said that molecules of different gasesin a mixture act independently of one another in in a mixture act independently of one another in exerting a force on the wall of the container.exerting a force on the wall of the container.

In other words, the frequency of collisions of In other words, the frequency of collisions of one gas is independent of the presence of one gas is independent of the presence of other gasesother gases

Dalton’s Law of Partial PressuresDalton’s Law of Partial Pressures

DALTON’S LAW OF PARTIAL PRESSURES DALTON’S LAW OF PARTIAL PRESSURES statesstates

the following:the following:

The sum of the partial pressures of all theThe sum of the partial pressures of all thecomponents in a gas mixture is equal to components in a gas mixture is equal to

the totalthe totalpressure of the gas mixturepressure of the gas mixture

In other words: PIn other words: Ptotaltotal = P = Pgas1gas1 + P + Pgas2gas2 + P + Pgas3gas3 + … + …

PPtottot = P = PHeHe + P + PNeNe + P + Parar

PPtottot = 1 atm + 2 atm + 3 atm = 6 atm = 1 atm + 2 atm + 3 atm = 6 atm

Partial Pressure ProblemPartial Pressure Problem

A diving tank contains a mixture of Oxygen andA diving tank contains a mixture of Oxygen andNitrogen. The pressure exerted by these gases Nitrogen. The pressure exerted by these gases Is 7.2 atm. The partial pressure of the NitrogenIs 7.2 atm. The partial pressure of the NitrogenIs 5.76 atm. What is the pressure exerted by Is 5.76 atm. What is the pressure exerted by The Oxygen in The Oxygen in atm.atm. & & KPaKPa??

PPtottot = P = PO2O2 + P + PN2N2

7.2 atm = P7.2 atm = P0202 + 5.76 atm + 5.76 atmPPO2O2 = 1.44 atm = 1.44 atmPPO2O2 = 1.44 x 101.3 = = 1.44 x 101.3 = 145.87 Kpa145.87 Kpa

Partial Pressure Problem 2Partial Pressure Problem 2The gases carbon dioxide, oxygen and ArgonThe gases carbon dioxide, oxygen and Argonare mixed in a tank. All gases have the sameare mixed in a tank. All gases have the samePartial pressure, and the total pressure of thePartial pressure, and the total pressure of theTank is 48,420 Pascals.Tank is 48,420 Pascals.What is the partial pressure of OWhat is the partial pressure of O22??

Sol’n:Sol’n: PPtottot = P = PCO2CO2 + P + PO2O2 + P + PArAr

48,420 = 3P (since they’re all equal)48,420 = 3P (since they’re all equal)

PPO2O2 = 48,420/3 = = 48,420/3 = 16,14016,140 Pascal Pascal

Diffusion and EffusionDiffusion and EffusionDiffusion: Diffusion:

Movement of one gas through another gas from a area ofMovement of one gas through another gas from a area ofHigh concentrationHigh concentration to an area of to an area of low concentrationlow concentration

When you smell the skunk in the backyard or the fish in When you smell the skunk in the backyard or the fish in The kitchen its The kitchen its diffusiondiffusion of gas molecules that bring the of gas molecules that bring theSmell to your noseSmell to your nose

Diffusion and EffusionDiffusion and EffusionEffusion:Effusion:

A process closely related to A process closely related to diffusiondiffusion..

It’s the movement of molecules or atoms through a tinyIt’s the movement of molecules or atoms through a tinyHole, one so small that only one molecule at a time can Hole, one so small that only one molecule at a time can Pass through Pass through

An example of effusion is the An example of effusion is the deflationdeflation of a of a helium filled balloon overnight.helium filled balloon overnight.

Graham’s law of effusionGraham’s law of effusion

In 1846 Thomas Graham studied the rates at which In 1846 Thomas Graham studied the rates at which Different gases move through a small opening into a Different gases move through a small opening into a Vacuum.Vacuum.

What he discovered was…. What he discovered was….

GRAHAM’S LAW ALSO APPLIES TO GRAHAM’S LAW ALSO APPLIES TO DIFFUSIONDIFFUSION ! !

Gases with smaller MW effuse (or diffuse) more rapidlyGases with smaller MW effuse (or diffuse) more rapidlyThan gases with larger MW’sThan gases with larger MW’s

SlowerSlower

fasterfaster

Graham’s law of effusionGraham’s law of effusionProblem: Arrange the following gases from Problem: Arrange the following gases from highest tohighest to

lowestlowest rate of diffusion rate of diffusion

He ClHe Cl22 Ne O Ne O22 H H22 N N22 Kr Kr

HH22 He Ne N He Ne N22 O O22 Cl Cl22 Kr Kr