Chapter 18

Dalton’s Law of Partial Pressures

We all live in the ocean of air, called the atmosphere.

Barometers and Standard Atmospheric Pressure

Barometers and Standard Atmospheric Pressure

• Standard atmospheric pressure defined as the pressure sufficient to support a mercury column of 760mm high. (units of mmHg, or torr).

• Another unit was introduced to simplify things, the atmosphere (1 atm = 760 mmHg).

• 1 atm = 760 mmHg = 760 torr = 101.3 kPa.

STP standard temperature and pressure

Standard temperature 0°C or 273 K

Standard pressure 1 atm (or equivalent)

Dalton’s Law of Partial Pressure • The total pressure of a mixture of gases is the sum of the

partial pressures of all the gases in the container.• The contribution each gas makes to the total pressure of a

mixture of gases is known as the partial pressure of that gas.

• Ptotal = PA + PB + PC

• Ptotal = 100 kPa + 250 kPa + 200 kPa = 550 kPa

A550 kPa

Turn to the “Dalton’s Law of Partial Pressures” sheet in your notebook.

Air is composed primarily of four gases: nitrogen (593.4 torr), argon (7.098 torr), carbon dioxide (0.2508 torr), and oxygen. What is the

partial pressure of oxygen at standard atmospheric pressure?

• 593.4 torr + 7.098 torr + 0.2508 torr = 600.7488 torr

≈ 600.7 torr

• 760 torr – 600.7 torr = 159.3 torr ≈ 159 torr

Air is composed primarily of four gases: nitrogen (593.4 torr), argon (7.098 torr), carbon dioxide (0.2508

torr), and oxygen. What percent of air is nitrogen?

593.4 torr

760 torrx 100 = 78.1%

Air is composed primarily of four gases: nitrogen (593.4 torr), argon (7.098 torr), carbon dioxide (0.2508 torr), and oxygen. What is the partial pressure in kPa of argon gas at standard

atmospheric pressure?

7.098 torr

Air is composed primarily of four gases: nitrogen (593.4 torr), argon (7.098 torr), carbon dioxide (0.2508 torr), and oxygen. What is the partial pressure in kPa of argon gas at standard

atmospheric pressure?

7.098 torr

760 torr101.3 kPa = 0.946 kPa

What would be the partial pressure of oxygen on top of a high mountain where the air pressure is only 534 mm Hg?

159 torr

760 torr= X

534 torr

x = 112 torr

Remember from the first problem that the partial pressure of oxygen in air is 159 torr

What percent less oxygen is dissolved into the blood on top of the mountain as compared to sea level?

112 torr

159 torrx 100 = 70.4%

100 – 70.4 = 29.6% less

Mount Everest

Endurance Training

Homework

Dalton’s Law of Partial Pressures and Ideal Gases Worksheet