Page 1 and 2 from Gas notes

The Nature of Gases

Goals for this section:

-          Describe the assumptions of the kinetic theory as it applies to gases

-          Interpret gas pressure in terms of kinetic theory

-          Define the relationship between Kelvin temperature and average kinetic energy

-          Terms to know: kinetic energy, kinetic theory, gas pressure, vacuum, atmospheric pressure, barometer, pascal (Pa), standard atmosphere (atm)

I.                   Kinetic Theory

a.       The word kinetic refers to motion

b.      The energy an object has because of its motion is called kinetic energy

c.       According to the kinetic theory, all matter consists of tiny particles that are in constant motion.

d.      3 Assumptions of kinetic theory:

                                                              i.      The particles in a gas are considered to be small, hard spheres with an insignificant volume
 - This means only the volume between particles matters
- particle size doesn’t matter

                                                            ii.      The motion of the particles in a gas is rapid, constant and random

                                                          iii.      All collisions between particles in a gas are perfectly elastic- this means there are no attraction

                                    - Particles are too far apart to be attracted to each other

II.                Gas pressure results from the force exerted by a gas per unit surface area of an object

a.       This means: gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.

b.      An empty space with no particles and no pressure is called vacuum                                     .

c.       Atmospheric pressure results from the         collisions of atoms and molecules in air with objects in air with objects.

d.      A                     barometer                                            is a device that is used to measure atmospheric pressure.

III.             The SI unit of pressure is the pascal (Pa).  However, kPa is usually used. 
1000 Pa = 1 kPa

a.      Standard pressure is    101.3 kPa or 1 atm                                                      . This is also the pressure at sea level.  

b.       

IV.             Average Kinetic Energy

a.       The particles in any collection of atoms or molecules at a given temperature have a wide range of kinetic energies. Most of the particles have kinetic energies  somewhere in the middle of this range.

b.      

c.       Absolute zero (0 K, or –273.15°C) is the temperature at which the motion of particles theoretically ceases.

                                                              i.      Particles would have no kinetic energy at absolute zero.

                                                            ii.      Absolute zero has never been produced in the laboratory.

d.      The Kelvin temperature of a substance is       directly proportional                                                               to the average kinetic energy of the particles of the substance.

                                                              i.      This means that :
As temperature increases, KE             increases          As temperature decreases, KE            decreases

Notes on your own - Properties of Gases (there are 8 questions)

Goals for this section:

-          Explain why gases are easier to compress than solids and liquids

-          Describe the 3 factors that affect air pressure

-          Explain how changes in these 3 factors result in changes in air pressure

-          Terms to know: Compressibility

1. Compressibility is a measurement of how much the volume of matter decreases under pressure. When a person collides with an inflated airbag, the compression of the gas absorbs the energy of the impact.
1. Why does a gas compress more than a solid or liquid?          Because the space between particles in the gas is much greater than the distance between particles in liquid and solid. Also, under pressure, the particle in gas are forced closer together
2. At room temperature, the distance between particles in an enclosed gas is about 10 times the diameter of a particle
2. There are three things that can impact gas pressure.  What are they?  (hint:  think about the warnings on aerosol cans, how your tires behave in the summer vs. the winter, how you change the pressure in your tires, and what happens to a balloon if you squeeze it)The amount of gas, volume and temperature. With raising the pressure exerted by a contained gas, it is reducing its volume. An increase in the temperature of an enclosed gas causes an increase in its pressure. If you inflate an air raft, for example, the pressure inside the raft will increase
3. Four variables are generally used to describe a gas. The units and the symbol used to indicate the 4 variables are listed below. List what the symbol stands for.
1.  Pressure                                              (P) in kilopascals
2.  volume                                               (V) in liters
3.  Temperature                                       (T) in kelvins
4. the number of moles                           (n).