The Nature of Gases – Part 2
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The Nature of Gases – Part 2 Gas Pressure
description
Gas Pressure. The Nature of Gases – Part 2. Objectives. When you complete this presentation, you will be able to: describe gas pressure in terms of the motion of gas particles. describe the invention of the barometer. describe the derivation of the units of pressure. - PowerPoint PPT Presentation
Transcript of The Nature of Gases – Part 2
The Nature of Gases – Part 2
Gas Pressure
Objectives
When you complete this presentation, you will be able to: describe gas pressure in terms of the
motion of gas particles. describe the invention of the barometer. describe the derivation of the units of
pressure. convert between the units of pressure.
Introduction
Gas pressure is the result of the force of gas molecules exerted on a surface.
The force of a single molecule of gas in insignificant, but the force of trillions of molecules becomes measurable.
A vacuum is a volume where there are no gas molecules bouncing off a surface.
Atmospheric pressure results from the collision of air molecules with objects.
Measuring Pressure
We measure the pressure of a gas by using an instrument called a barometer.
The barometer was invented in 1643 by the Italian physicist Evangelista Torricelli.
He made a barometer from a tube of glass (sealed at one end) and a trough of mercury.
Measuring Pressure
We measure the pressure of a gas by using an instrument called a barometer.
The barometer was invented in 1643 by the Italian physicist Evangelista Torricelli.
He made a barometer from a tube of glass (sealed at one end) and a trough of mercury.
Measuring Pressure
We measure the pressure of a gas by using an instrument called a barometer.
The barometer was invented in 1643 by the Italian physicist Evangelista Torricelli.
He made a barometer from a tube of glass (sealed at one end) and a trough of mercury.
The air pressure on the Hg held the column up.
Pressure Units
The air pressure in a barometer is measured by measuring the height of the mercury column.
Under standard conditions, a column of mercury will be 760 mm in height.
So, we say that 1 atmosphere of pressure (1 atm) is equal to 760 mm Hg.
Pressure Units
Another unit for pressure uses SI units for force (newtons, N) per area (m2) which is called a Pascal, (Pa).
Under standard conditions, 1 atm of pressure is equal to 101,300 Pa = 101.3 kPa.
Pressure Units
Our conversions are:
1.000 atm = 760.0 mm Hg = 101.3 kPa
Let’s do some examples
Example 1
A container of oxygen gas has a pressure of 0.450 atm. Find the pressure in mm Hg and kPa.
Conversions:1.000 atm = 760.0 mm Hg = 101.3 kPa
Solution:0.450 atm1 = =
760.0 mm Hg1.000 atm 342 mm
Hg
0.450 atm1 = =
101.3 kPa1.000 atm 45.6 kPa
Example 2
A container of nitrogen gas has a pressure of 855 mm Hg. Find the pressure in atm and kPa.
Conversions:1.000 atm = 760.0 mm Hg = 101.3 kPa
Solution:855 mm Hg1 = =
1.000 atm760.0 mm
Hg
1.13 atm
855 mm Hg1 = =
101.3 kPa760.0 mm
Hg
114 kPa
Example 3
A container of hydrogen gas has a pressure of 97.3 kPa. Find the pressure in atm and mm Hg.
Conversions:1.000 atm = 760.0 mm Hg = 101.3 kPa
Solution:97.3 kPa1 = =
1.000 atm101.3 kPa
0.961 atm
97.3 kPa1 = =
760.0 mm Hg101.3 kPa
730 mm Hg
Practice Problems
Fill in the blanks for each of the following pressures
Conversions:1.000 atm = 760.0 mm Hg = 101.3 kPa
atm mm Hg kPa
3.00
950
76.0
0.742
600
258
2,280 304
1.25 127
0.750 570
564 75.2
0.789 80.0
2.55 1,940
Summary
Gas pressure is the result of the force of gas molecules exerted on a surface.
Atmospheric pressure results from the collision of air molecules with objects.
We measure the pressure of a gas by using an instrument called a barometer invented in 1643 by the Italian physicist Evangelista Torricelli.
Our conversions are:1.000 atm = 760.0 mmHg = 101.3 kPa
