Gasses
Kinetic molecular theory
Pressure
Introduction
• Earth’s atmosphere is a gaseous solution
composed of mostly nitrogen and oxygen
• The atmosphere is important for life on earth
– Provides a medium for many chemical reactions
with waste products
– Shields the Earth from harmful radiation
– Retains heat on earth’s surface
• The behavior of gas particles contributes to
their important properties
States of Matter
• Atoms/Molecules in all states of matter have
attractive forces
– Strongest in solids, weakest in gasses
– Affected by changes in temperature
• Kinetic energy (KE) = energy of motion
• Temperature = a measurement of kinetic energy
Solids
Definite shape
X
Definite volume
X
X
Gases
X
X
Takes the shape of its container
Cannot be compressed
Liquids
X
X
Kinetic Molecular Theory
• Gasses consist of tiny particles
• The particles are so small (compared between
the distances between them) that the individual
particles have nearly no volume
• The particles are in constant random motion,
colliding with the walls of the container. These
collisions cause the pressure exerted by the gas.
• The particles are assumed not to attract or repel
each other.
• The average kinetic energy of the gas particles is
proportional to the Kelvin temperature of the
gas.
Pressure
• Gas fills any container uniformly
– It is evenly spread out
• Gasses exert pressure on their surroundings
– Example: when you blow up a balloon, the gasses
inside push against the sides and keep it firm.
• A Barometer measures atmospheric pressure
– Invented by Evengelista Torricelli in 1643
• Atmospheric pressure results from the air
being pulled by gravity
– Varies with altitude
– Changes with weather conditions
Units of Pressure
• The units for pressure are based on the height of
the mercury column (in millimeters) that the gas
pressure can support
– mm Hg (millimeters of mercury) is also called torr
• Standard atmospheres (abbreviated atm) are also
used.
1 standard atm = 1.000 atm = 760.0 mm Hg = 760.0 torr
• The SI unit for pressure is the pascal (Pa)
1 atm = 101,325 Pa
• Engineers use pounds per square inch (psi)
1.000 atm = 14.69 psi
Pressure Unit Conversions
Convert the following to atmospheres:
1.
2.
3.
109.2 kPa (1 kPa = 1000 Pa)
781 torr
15.2 mm Hg
Convert the following into units of mm Hg:
4.
5.
6.
9.75 psi
121.4 kPa
1.14 atm
Convert the following into kilopascals (kPa)
7.
8.
9.
10.
105,390 Pa
764 mm Hg
1.29 atm
697 torr