According to Dalton’s Law, the **total pressure** inside a container is obtained by adding all the **partial pressures** of each non-reacting gas.

**Concept:** Understanding Dalton's Law

Welcome back guys. In this video, we're going to take a look at the partial pressure of gases. Now, what do I mean by partial pressure? What we said in the beginning, that pressure equals force over area. We saw a picture of the container with several different types of gas particles. We're going to say that the total pressure inside of that container comes from all the pressures that each of those particles added up.

Let's say we wanted to look at the pressure of one of those gas particles and ignore the others. The pressure of that one single gas particle would be that gas particles partial pressure. It just means the pressure of a gas when it surrounded by a bunch of different gases. We're not looking at the total pressure. We're looking at that gas particles individual pressure. That individual pressure is partial pressure.

We're going to say Dalton's law states that, 'In a container of unreacting gases,' that means that these gases are just bouncing off of each other. They're not connecting together to give me a new compound. 'The total pressure of the container is the sum of the partial pressure of the individual gases.' All these mean is let's say we have a container and its filled with three types of gases. It's filled with O2, argon and neon gas.

Let's say that the pressure of the oxygen gas is 0.3 atm and argon is 0.1 atm and neon is 0.3 atm. We'd say that each of them has those individual pressures—that's their partial pressures. Dalton's law says, while the total pressure inside of the container is just each of them added up together. According to Dalton's law, the total pressure equals 0.7 atm, and that 0.7 atm comes from us adding up each of those individual pressures together.

**Concept:** Understanding mole fraction and partial pressure

We're going to say that the total pressure due like we said to the total number of moles of each of these gas particles. So pressure and moles are connected together. We're going to say the partial pressure of each gas molecule is a total pressure multiplied by the mole fraction of each gas particle or gas molecule. What the heck does that mean?

What I'm saying here is, the pressure of a gas, of any individual gas is equal to its mole fraction, mole fraction is X. We're going to say, 'What the heck is mole fraction?' Mole fraction is the moles of that gas divided by the total moles of all the gases. If we're looking for example the mole fraction of neon gas, it'd be the moles of neon divided by the moles of oxygen, argon plus neon on the bottom. That would give us the mole fraction of neon.

Once we get the mole fraction of a gas, we would multiply times the total pressure. That would then give me just the pressure of that one gas. Here this is just partial pressure. I know these ideas are kind of abstract, so that's why we're going to move on to the next question, the example. This is going to show us how exactly does, how do we find the partial pressure of the gas and does that relate to the mole fraction of that gas.

The **partial pressure** of a gas is based on the moles of that gas. The relationship of the different moles of gases helps us determine the **mole fraction** of each gas.

**Example:** A container has 16.7 g O_{2}, 8.1 g H_{2} and 35.2 g N_{2} and contains a total pressure of 0.83 atm. Calculate the mole fraction of O_{2} and its partial pressure.

**Problem:** A gas mixture with a total pressure of 812 mmHg contains the following gases at with their partial pressures: Cl_{2 }= 210 mmHg, H_{2} = 180 mmHg, CO_{2} = 215 mmHg. If argon gas is also present calculate its mole fraction.

A 1.00 L flask is filled with 1.00 g of argon at 25 °C. A sample of ethane vapor is added to the same flask until the total pressure is 1.250 atm.

i) What is the partial pressure of argon, *P_{Ar}*, in the flask?

Express your answer to three significant figures and include the appropriate units.

ii) What is the partial pressure of ethane, *P_{ethane}*, in the flask?

Express your answer to three significant figures and include the appropriate units.

Watch Solution

Chloroform and methanol form an ideal solution. The solution boils at 22°C and 0.255 atm. At 22°C the vapor pressures of methanol and chloroform are 0.192 atm and 0.311 atm respectively. What is the mole fraction of chloroform in the solution?

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A vessel contains 0.1 mol H_{2} gas, 0.1 mol N_{2 }gas, and 0.3 mol NH_{3} gas. The total pressure is 1000 torr. What is the partial pressure of

the H_{2} gas?

1. 1000 torr

2. 500 torr

3. 100 torr

4. 800 torr

5. 200 torr

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A mixture of 10.0 g of Ne and 10.0 g Ar have a total pressure of 1.6 atm. What is the partial pressure of Ne?

A) 1.3 atm

B) 1.1 atm

C) 0.80 atm

D) 0.40 atm

E) 0.54 atm

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Determine the vapor pressure of a solution at 25°C that contains 76.6 g of glucose (C_{6}H_{12}O_{6}) in 250.0 mL of water. The vapor pressure of pure water at 25°C is 23.8 torr. (Density of water is 1.0 g/mL)

A) 70.8 torr

B) 72.9 torr

C) 23.1 torr

D) 22.9 torr

E) 7.29 torr

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A 100 L balloon is blown up with a mixture of gases. The mixture contains 2.1 moles of oxygen, 3.5 moles of nitrogen, and 1.8 moles of helium. Find the partial pressure for the oxygen if the balloon is at atmposheric pressure.

a. 0.28 atm

b. 0.47 atm

c. 0.24 atm

d. 0.22 atm

e. 0.78 atm

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A mixture of 0.50 moles of Ne and 0.25 moles of Ar has a total pressure of 1.6 atm. What is the partial pressure (in atm) of Ne?

A. 1.1 atm

B. 1.3 atm

C. 0.40 atm

D. 0.80 atm

E. 0.54 atm

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Calculate the vapor pressure at 25^{◦}C of a mixture of benzene and toluene in which the mole fraction of benzene is 0.650. The vapor pressure at 25^{◦}C of benzene is 94.6 torr and that of toluene is 29.1 torr.

a. 51.3 torr

b. 61.5 torr

c. 84.4 torr

d. 124 torr

e. 71.7 torr

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What is the vapor pressure of a solution with a benzene to octane molar ratio of 2:1?

(A) 120 mmHg

(B) 320 mmHg

(C) 400 mmHg

(D) 680 mmHg

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In a mixture of N _{2} and O_{2} gases, the mol fraction of N _{2 }is found to be 0.700. The total pressure of the mixture is 1.42 atm. What is the partial pressure of O_{2} in the mixture?

a) 0.211 atm

b) 0.426 atm

c) 0.493 atm

d) 0.994 atm

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A flask at equilibrium contained 1.00 mol of N _{2} gas, 2.00 mol of H_{2} gas, and 3.00 mol of He gas. The total pressure in the container was 1.00 atm. What was the partial pressure of the He gas in torr?

a) none of the given answers

b) 380

c) 2280

d) 760

e) 4560

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A mixture of hydrogen and helium is 25.0% hydrogen by mass. What is the partial pressure of hydrogen (in atm) in the mixture at STP?

a) 0.460

b) 0.399

c) 0.520

d) 0.250

e) 0.380

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0.40 g of H_{2}, 20.0 g CO_{2, }and 14.00 g of O_{2 }are placed into a 5.0 L container at 18°C. What is the partial pressure of CO_{2 }gas and what is the total pressure in the container?

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A mixture of He and O _{2} is placed in a 4 L flask at 300 K. The partial pressure of the He is 2.7 atm and the partial pressure of the O_{2} is 1.4 atm. What is the mole fraction of O _{2}?

a. 0.341

b. 0.481

c. 0.518

d. 0.659

e. 0.224

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A mixture of 30.0 g ammonia (MW 17 g/mol), 30.0 g oxygen (MW 32 g/mol) and 30.0 g propylene (MN 42 g/mol) occupies 10.0 L at 100.0°C. What is the partial pressure (atm) of the oxygen?

a. 2.18 atm

b. 8.56 atm

c. 5.88 atm

d. 2.87 atm

e. None of the above

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A gaseous mixture of O _{2} and N_{2} contains 39.8% nitrogen by mass. What is the partial pressure of oxygen in the mixture if the total pressure is 505 mmHg?

a. 171 mmHg

b. 60 mmHg

c. 870 mmHg

d. 288 mmHg

e. 700 mmHg

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The partial pressure of an ideal gas is equal to:

a. The pressure it would exert if it were at high pressure, same volume, and alone in a container

b. The pressure it would exert if it were at low pressure, same volume, and alone in a container.

c. The pressure it would exert if it occupied the same volume, alone in a container, at the same temperature.

d. The pressure it would exert if it were at low temperature, same volume, and alone in a container.

e. The pressure it would exert if it were at high temperature, same volume, and alone in a container.

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A mixture of 10.0 g of Ne and 10.0 g of Ar has a total pressure of 1.6 atm. What is the partial pressure of Ne?

a. 1.1 atm

b. 0.8 atm

c. 0.54 atm

d. 0.40 atm

e. 1.3 atm

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A 4.0 L flask containing N_{2} at 15 atm is connected to a 4.0 L flask containing H _{2} at 7.0 atm and the gases are allowed to mix. What is the mole fraction of N_{2}?

1. 0.75

2. Cannot be determined

3. 0.93

4. 0.26

5. 0.32

6. 0.68

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A mixture of CO, CO_{2} and O_{2} is contained within a 275 mL flask at 0°C. if the total pressure is 780 torr, the CO has a partial pressure of 330 torr and the CO_{2} has a partial pressure of 330 torr, what is the partial pressure of O_{2}?

1. 330 torr

2. 900 torr

3. 120 torr

4. 780 torr

5. 660 torr

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A mixture of oxygen and helium is 92.3% by mass oxygen. It is collected at atmospheric pressure (687 torr). What is the partial pressure of oxygen in this mixture?

1. 446 Torr

2. 414 Torr

3. 688 Torr

4. 299 Torr

5. 333 Torr

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A mixture of N _{2}, O_{2} and Ar have mole fractions of 0.25, 0.65, and 0.10, respectively. What is the pressure of N_{2} if the total pressure of the mixture is 3.9 atm?

A) 2.5 atm

B) 0.39 atm

C) 0.67 atm

D) 0.98 atm

E) 1.33 atm

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A gaseous mixture containing 1.5 mol Ar and 3.5 mol CO _{2} has a total pressure of 7.0 atm. What is the partial pressure of CO_{2}?

a) 1.8 atm

b) 2.1 atm

c) 3.5 atm

d) 4.9 atm

e) 2.4 atm

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A mixture of He and O_{2} is placed in a 4 L flask at 300 K. The partial pressure of the He is 2.7 atm and the partial pressure of the O_{2} is 1.4 atm. What is the mole fraction of O _{2}?

a. 0.341

b. 0.481

c. 0.518

d. 0.659

e. 0.224

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