kinetic theory
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Gases
Part 1: Kinetic Molecular Theory
Kinetic Molecular Theory
describes the behavior of gases in terms of particles in motion.
makes several assumptions about the sizemotion, and energy of gas particles.
Assumptions
Particle size Particle motion Particle energy
Particle Size
Gases consist of small particles that are separated from one another by empty space.
The volume of the particles is small compared with the volume of the empty space.
Gas has Mass
Particle motion
Gas particles are in constant, random motion.
Particles move in a straight line until they collide with other particles or with the walls of their container.
Elastic Collisions
Collisions between gas particles are elastic.
An elastic collision is one in which no kinetic energy is lost.
Particles move very fast
Particle energy
Kinetic energy is a function of the mass and speed of a particle.
In a sample of a single gas, all particles have the same mass but all particles do not have the same velocity.
Therefore, all particles do not have the same kinetic energy.
Kinetic Energy and Momentum
Properties of Gases
Low density Compressible Diffuses
Low density
Density – mass per unit of volume (g/cm3) Density of gasses is much lower than the
density of solids or liquids.
Compressible
Gasses can be compressed Compression – can be pushed
into a smaller volume Expansion – can be pulled into a
greater volume
Diffusion
the movement of one material through another.
particles diffuse from an area of high concentration to one of low concentration
Temperature and Pressure
Kinetic theory explains the temperature and pressure of gassesHow fast the molecules of a gas are goingHow heavy the molecules are
Temperature
Temperature is a measure of the average kinetic energy of the particles in a sample of matter.
In other words…
Temperature is related toHow fast the molecules of a gas are movingHow often the molecules hit the walls of the
container
Gas has temperature
Pressure
defined as force per unit area. Gas particles exert pressure when they
collide with the walls of their container.
In other words…
Pressure is related toHow fast the molecules of a gas are movingHow much the particles weighHow hard the molecules hit the walls of the
container
Gas has pressure
Measuring Pressure A barometer is an instrument
used to measure atmospheric pressure.
A manometer is an instrument used to measure gas pressure in a closed container.
Pressure Units SI unit of pressure is the pascal (Pa). It is
named for Blaise Pascal. One pascal is equal to a force of one
newton per square meter: 1 Pa= 1 N/m2.
Other Pressure Units engineers often report pressure as pounds
per square inch (psi). pressures measured by barometers and
manometers can be reported in millimeters of mercury (mm Hg).
Air pressure
At sea level, the average air pressure is 760 mm Hg when the temperature is 0°C.
Air pressure often is reported in a unit called an atmosphere (atm). One atmosphere is equal to 760 mm Hg or 760 torr or 101.3 kilopascals (kPa).
Temperature and Pressure
Temperature and pressure are directly proportional
As one goes up, the other goes up As one goes down, the other goes down
Temperature and Pressure
Temperature and volume
Volume and Pressure