Dalton’s Law of Dalton’s Law of Partial PressuresPartial Pressures

A Tutorial Created By:A Tutorial Created By:

Beth Dinich & Anne KleinfeldtBeth Dinich & Anne Kleinfeldt

What is it?What is it?

Dalton’s Law states that the Dalton’s Law states that the pressure exerted by a mixture of pressure exerted by a mixture of gases equal the sum of the gases equal the sum of the partial pressures of the gases in partial pressures of the gases in the mixture.the mixture.

Check all of your units, Check all of your units, they must be the same. they must be the same.

Lets start with Lets start with checking and checking and converting our converting our pressures, if pressures, if necessary.necessary.

Standard Pressures Standard Pressures are as follows:are as follows:

1atm1atm

760mm or torrs760mm or torrs

101.325kpa101.325kpa

Lets Try ConvertingLets Try Converting

If we are given 92.1 kpa you must transfer it to atm If we are given 92.1 kpa you must transfer it to atm using factor label.using factor label.

Put your given pressure on the top and the standard Put your given pressure on the top and the standard pressure for the given units on the bottom.pressure for the given units on the bottom.

The pressure that you are converting to will go as a The pressure that you are converting to will go as a standard pressure on the top of the given’s standard.standard pressure on the top of the given’s standard.

Let’s try some moreLet’s try some more

You are given 360 torrs and you need to You are given 360 torrs and you need to change it to kpa.change it to kpa.

You are given 1.73 atm and you need to convert it to mm.You are given 1.73 atm and you need to convert it to mm.

Don’t forget your Don’t forget your volumes!volumes!

All of your volume units must also be the All of your volume units must also be the same.same.

1 liter is 1000 ml.1 liter is 1000 ml. 1 ml is equal to 1 cm1 ml is equal to 1 cm33..

Examples:Examples: 1.356 liters = 1356 ml = 1356 cm1.356 liters = 1356 ml = 1356 cm33

5780 cm5780 cm33 = 5780 ml = 5.78 liters = 5780 ml = 5.78 liters

The EquationThe Equation

PPTT = = ∑ P∑ PXX

The total pressure is equal to the The total pressure is equal to the summation of the partial pressures.summation of the partial pressures.

PPTT = P = PAA + P + PBB + P + PCC + … + …

Let’s Try One Let’s Try One

PPTT=P=PAA+P+PBB+P+PCC+P+PDD

All of our pressures are in the same unit so we don’t All of our pressures are in the same unit so we don’t about converting those. Our volume has one unit in about converting those. Our volume has one unit in liters and the rest in milliliters. We need to change it.liters and the rest in milliliters. We need to change it.

0.5 l = 500 ml OK, we are ready to start.0.5 l = 500 ml OK, we are ready to start.

Here we go!Here we go!

Now add all of your partial pressures together Now add all of your partial pressures together and you will have your total pressure.and you will have your total pressure.

Let’s try another!Let’s try another!

You are given:You are given:

Work it out ! ! !Work it out ! ! !

Don’t forget to convert all of your Don’t forget to convert all of your pressures and volumes to one unit of pressures and volumes to one unit of either pressure or volume, respectively.either pressure or volume, respectively.

Use your standard pressures and Use your standard pressures and volumes to do this.volumes to do this.

While working on this problem we While working on this problem we decided to use atm for our pressure and decided to use atm for our pressure and ml for our volume.ml for our volume.

Converting to the same Converting to the same unitsunits

Here we changed all Here we changed all of our pressures that of our pressures that were not in atm to were not in atm to atm.atm.

Don’t forget to have all of your volumes in the same units!

Let’s keep going …Let’s keep going …

Adding the partial pressures gives us the total Adding the partial pressures gives us the total pressure:pressure:

Here’s the quiz …Here’s the quiz …

Grab a piece of scratch paper and begin.Grab a piece of scratch paper and begin. Question number one.Question number one. What is Dalton’s Law of Partial What is Dalton’s Law of Partial

Pressures?Pressures?

Question number two.Question number two. What is the equation for Dalton’s Law of What is the equation for Dalton’s Law of

Partial Pressures?Partial Pressures?

Here’s the hard one …Here’s the hard one … Question number three.Question number three. What is the total pressure of the following?What is the total pressure of the following?

Here are the answers . . . Here are the answers . . .

Answer to question one.Answer to question one. Dalton’s law of partial pressures is the Dalton’s law of partial pressures is the

pressure exerted by a mixture of gasses pressure exerted by a mixture of gasses equal to the sum of the partial pressures equal to the sum of the partial pressures of the gases in the mixture.of the gases in the mixture.

Answer to question two.Answer to question two. PPTT = = ∑ P∑ PXX

Answer to Question Answer to Question Number Three . . .Number Three . . .

152.7 kpa152.7 kpa How in the world do you get that???How in the world do you get that??? The first thing you do is convert all of your The first thing you do is convert all of your

pressures to kpa and volume to milliliters.pressures to kpa and volume to milliliters.

Here comes the rest . . .Here comes the rest . . .

Congratulations ! ! Congratulations ! ! !! You Are DONE ! You Are DONE !