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.
A
550 kPa
• Ptotal = PA + PB + PC
• Ptotal = 100 kPa + 250 kPa + 200 kPa = 550 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 torr
x 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
101.3 kPa
760 torr
= 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?
Remember from the first problem that the partial pressure of oxygen in air
is 159 torr
159 torr
760 torr
=
X
534 torr
x = 112 torr
What percent less oxygen is dissolved into the blood
on top of the mountain as compared to sea level?
112 torr
159 torr
x 100 = 70.4%
100 – 70.4 = 29.6% less
Mount Everest
Endurance Training
Homework
 Dalton’s Law of Partial Pressures and Ideal
Gases Worksheet