The Nature of Gases

1
The Nature of Gases
2
Kinetic Theory and a Model for Gases

• The word kinetic refers to motion.
• The energy an object has because of its motion is
  called kinetic energy.
• The kinetic theory states that the tiny particles
  in all forms of matter are in constant motion.

3
Kinetic Theory and a Model for Gases

• A gas is composed of particles, usually molecules
  or atoms.
• They have insignificant volume and are relatively
  far apart from one another.

4
Kinetic Theory and a Model for Gases

• The particles in a gas move rapidly in constant
  random motion. They travel in straight paths and
  move independently of each other.
• As a result, gases fill their
• containers regardless of
• the shape and volume of
• the containers.

5
Kinetic Theory and a Model for Gases

• All collisions between gas molecules are
  perfectly elastic.
• During an elastic collision, kinetic energy is
  transferred without loss from one particles to
  another, and the total kinetic energy remains
  constant.

6
Gas Pressure

• Gas pressure is defined as the force exerted by a
  gas per unit surface area of an object.
• Gas pressure is the result of simultaneous
  collisions of billions of rapidly moving gas
  particles with an object.

7
Gas Pressure

• If there are no gas particles present, there
  cannot be collisions, and there is no pressure.
  Such an empty space is called a vacuum.

8
Atmospheric Pressure

• Atmospheric pressure results from the collisions
  of air molecules with objects.
• Air exerts pressure on Earth because gravity
  holds air molecules in Earths atmosphere.
• Atmospheric pressure decreases as you climb a
  montain because the density of the Earths
  atmosphere decreases as elevation increases.

9
Atmospheric Pressure
10
Barometers

• Barometers are devices used to measure
  atmospheric pressure.
• This pressure is dependent on weather.

11
Pressure Units

• The SI unit of pressure is the pascal (Pa).
• Normal atmospheric pressure is about 100,000 Pa,
  that is 100 kilopascals (kPa).
• Two older unit of pressure are millimeters of
  mercury (mmHg) and atmospheres (atm).

12
Pressure Units

• One standard atmosphere (atm) is the pressure
  required to support 760 mm of mercury at 25 C.
• 1 atm 760 mm Hg 101.3 kPa

13
Converting Units of Pressure

• A tire pressure gauge records a pressure of 450
  kPa. What is this pressure measurement expressed
  in atmospheres and millimeters of mercury?

14
Converting Units of Pressure

• 1. what pressure, in kilopascals and in
  atmospheres, does a gas exert at 385 mm Hg?
• 2. the pressure at the top of Mount Everest is
  33.7 kPa. Is that pressure greater or less than
  0.25 atm?

15
Kinetic Energy and Temperature

• As a substance is heated, its particles absorb
  energy, some of which is stored within the
  particles.
• This stored energy, or potential energy, does not
  raise the temperature of the substance.
• The remaining absorbed energy speeds up the
  particles (increases their kinetic energy), which
  results in an increase in temperature.

16
Kinetic Energy and Temperature

• At any given temperature the particles of all
  substances, regardless of physical state, have
  the same average kinetic energy.

17
Kinetic Energy and Temperature

• Absolute zero (0K or -273.15C) is the temperature
  at which the motion of particles stops (no KE).
• The Kelvin temperature of a substance is directly
  proportional to the average kinetic energy of the
  particles of the substance.