Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
120 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
tube is placed so that the level of the mercury is determined by air
pressure. The mercury rises when the air pressure increases and falls
when the air pressure decreases.
A manometer is an instrument used to measure gas pressure in a
closed container. A flask containing gas is attached to a sealed Ushaped tube that contains mercury. The mercury is level across the
two arms of the U. When a valve between the flask and the tube is
opened, gas particles diffuse into the tube and push down on the
mercury. The difference in the height of the mercury in the two arms
of the U is used to calculate the pressure of the gas in the flask.
The pascal (Pa) is the SI unit of pressure. One pascal is equal to
a force of one newton per square meter. Some scientists use other
units of pressure. For example, engineers use pounds per square
inch. Barometers and manometers measure pressure in millimeters
of mercury (mm Hg). A unit called the torr is equal to 1 mm Hg.
Air pressure is often reported in a unit called an atmosphere
(atm). One atmosphere is equal to 760 mm Hg, 760 torr, or
101.3 kilopascals (kPa). These are all defined units; therefore,
they have as many significant figures as needed when used in
calculations.
Dalton’s law of partial pressures Dalton found that each gas in
a mixture exerts pressure independently of the other gases. Dalton’s
law of partial pressures states that the total pressure of a mixture of
gases is equal to the sum of the pressures of all the gases in the mixture, as shown below.
P total ϭ P 1 ϩ P 2 ϩ P 3 ϩ … P n
The portion of the total pressure (P total ) exerted by one of the gases
is called its partial pressure (P n ). The partial pressure of a gas
depends on the number of moles of the gas, the size of the container,
and the temperature of the mixture. The partial pressure of one mole
of any gas is the same at a given temperature and pressure.
▲
120 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
tube is placed so that the level of the mercury is determined by air
pressure. The mercury rises when the air pressure increases and falls
when the air pressure decreases.
A manometer is an instrument used to measure gas pressure in a
closed container. A flask containing gas is attached to a sealed Ushaped tube that contains mercury. The mercury is level across the
two arms of the U. When a valve between the flask and the tube is
opened, gas particles diffuse into the tube and push down on the
mercury. The difference in the height of the mercury in the two arms
of the U is used to calculate the pressure of the gas in the flask.
The pascal (Pa) is the SI unit of pressure. One pascal is equal to
a force of one newton per square meter. Some scientists use other
units of pressure. For example, engineers use pounds per square
inch. Barometers and manometers measure pressure in millimeters
of mercury (mm Hg). A unit called the torr is equal to 1 mm Hg.
Air pressure is often reported in a unit called an atmosphere
(atm). One atmosphere is equal to 760 mm Hg, 760 torr, or
101.3 kilopascals (kPa). These are all defined units; therefore,
they have as many significant figures as needed when used in
calculations.
Dalton’s law of partial pressures Dalton found that each gas in
a mixture exerts pressure independently of the other gases. Dalton’s
law of partial pressures states that the total pressure of a mixture of
gases is equal to the sum of the pressures of all the gases in the mixture, as shown below.
P total ϭ P 1 ϩ P 2 ϩ P 3 ϩ … P n
The portion of the total pressure (P total ) exerted by one of the gases
is called its partial pressure (P n ). The partial pressure of a gas
depends on the number of moles of the gas, the size of the container,
and the temperature of the mixture. The partial pressure of one mole
of any gas is the same at a given temperature and pressure.
▲