1. The Nature of Gases Regardless of their chemical identity,
all gases display similar physical behavior

2. Examples of gases A particle of gas can be: A single atom
He Ne Ar
A diatomic molecule
H I2 O2
A polyatomic molecule
CO2 CH4

3. Scientists use a model to explain the behavior of gases
Kinetic Molecular Theory
Describes the behavior of the sub-microscopic particles that make up a gas
Gases are composed of tiny particles, either atoms or molecules, each of which has a mass.
Gas particles are separated by large distances relative to their size. The particles are so small and the distances between them so great that the volume of the particles themselves is negligible.

4. The gas particles are in constant, rapid, random motion.
Gases exert pressure because their particles frequently collide with the walls of the container and with each other. Between collisions the particles travel in straight lines.

5. Physical properties of gases
Gases have mass
A basketball filled with air weighs more than an empty basketball.
It is easy to compress a gas
Squeeze a balloon.
Gases fill their containers completely.
A balloon fills evenly…all the gas does not concentrate on one side.

6. Physical properties of gases
Different gases move through each other quite rapidly in a process called diffusion.
The smell of cooking spreads.
Gases exert pressure.
Ears pop going up or down hills.
The pressure of a gas depends on its temperature.
Check tire pressure on hot or cold days!

7. Physical properties of gases
Because gas particles keep colliding without slowing down, the collisions are elastic (no energy or motion is lost)
The average kinetic energy of gases depends only on the temperature of the gases.
KE = ½ mv2
The higher the temperature, the higher the kinetic energy. Mass is constant, so particles speed up as the temperature increases.
Gas particles exert no force on each other.

8. How do we measure gases? Four variables Amount of gas n
Volume of gas V
Temperature of gas T
Pressure of gas P

9. Amount of gas The amount of a gas is measured in moles
The variable used to represent this is
n= number of moles
If a problem expresses the amount in grams, convert to moles using the molar mass.
n = mole = mass (g) / molar mass (g/mol)

10. Volume of gas V = volume = liters = L
The volume of a gas is often measured in liters
The variable used to represent this is
V = volume = liters = L
If a problem expresses the amount in other units you may convert to liters, but you don’t always need to.

11. T = temperature = 0C = K Temperature of a gas
The temperature of a gas is expressed in degrees centigrade (or Celsius) and converted to Kelvin
The variable used to represent temperature is
T = temperature = 0C = K
The Kelvin scale uses the same size degrees, but it starts at absolute zero, C.
To convert 0C to K, add 273.2
T (K) = 0C

12. Pressure of a gas P = pressure = different units are used
The variable used to express pressure is
P = pressure = different units are used
Pressure exerted by air in the atmosphere is atmospheric pressure. The mass of air is attracted by the gravity of the earth.
The force exerted on one square unit of area, say one meter, equals atmospheric pressure.

13. Pressure of a gas SI unit of force is the newton
Pressure is calculated in units of force per unit area.
P=F/A
SI unit of force is the newton
One newton of force exerted on one square meter of area = pascal = Pa
P = force (newton)/ area (square meter)
One pascal is small, so we often use kilopascals, kPa

14. STP Standard Temperature and Pressure STP stands for
Standard Temperature = K
Standard Pressure = 1 atm
You will often see this in gas law problems. It expresses the conditions of temperature and pressure described above.

15. Measure Pressure
Barometers measure pressure by noting the change in the level of mercury in a tube caused by the force of the atmosphere
Manometers are used to measure the pressure of a gas in a closed containers

16. Common Units of Pressure
1 pascal (Pa) = 1 newton of force / 1 square meter of area
1 kiloPascal (kPA)= 1000 pascal
1 atmosphere (atm) = 101,325 pascal (Pa)
1 atm = 760 mm Hg = 760 torr
1 atm = lb/sq in (psi)
1 bar = 100,000 Pa = atm