1. AIM: What are the general properties of gases and what is PRESSURE
AIM: What are the general properties of gases and what is PRESSURE ? Atmospheric pressure Units Gas pressure

2. Gases
Gases fill completely the container they are in (INDEFINITE VOLUME).
Gases assume the shape of the container they are in (INDEFINITE SHAPE).
Gas particles are separated from each other and move fast.
Gases are fluids, have low densities and are highly compressible.

3. Air Pressure or Atmospheric pressure
Is the force that the atmosphere exerts over the surface of the Earth.
It depends on the weather.
It changes with altitude.
It is measured with a BAROMETER.

4. Atmospheric pressure is the weight of air per unit of area.

5. Barometer
Evangelista Torricelli made the first barometer in 1644

6. UNITS FOR PRESSURE ATMOSPHERE = atm Torricelli = torr
Millimiters of Mercury = mm of Hg
KiloPascal = kPa

7. Normal Atmospheric Pressure (the pressure at sea level)
1 atm = kPa = 760 mm of Hg

8. November 14
BOYLE’S LAW
Relationship between pressure and volume for a gas

9. STP - STANDARD TEMPERATURE AND PRESSURE
Table A
0 0 C or 273 K
1 atm=101.3 kPa=760 mm of Hg=760 torr

10. Gas pressure Gas particles are in continuous motion.
Gases exert pressure by colliding with the walls of the container they are in.
The force exerted over the area of the wall is the pressure of the gas.
The greater the number of gas particles in a container the greater the pressure.

11. Collision against the walls of the container exert pressure

12. Gases
Have indefinite shape and indefinite volume. Gases will assume the shape and volume of the container the are in.
The particles inside a gas are in constant motion.
Gas particles exert pressure against the walls of the container

14. Boyle’s Law (1644)
The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure.
WHEN PRESSURE INCREASES THE VOLUME DECREASES (AT CONSTANT TEMPERATURE)

15. As P and V are inversely proportional
A plot of V versus P results in a curve at constant T
PV = k

16. EQUATION FOR BOYLE’S LAW PROBLEMS
P1 X V1 = P2 X V AT CONSTANT T
INITIAL FINAL

17. Review of Boyle’s Law problems
Relationship between temperature and volume of a gas at constant pressure- Charles’ Law
TEST ON GASES THURSDAY

18. Jacques Charles -Charles’ Law - 1802

19. V = k T Charles’s Law A plot of V versus T will be a straight line.
The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature. V T
= k
A plot of V versus T will be a straight line.

20. EQUATION FOR CHARLES’ LAW PROBLEMS
T1 / V1 = T2 / V AT CONSTANT P
INITIAL FINAL
REMEMBER THAT TEMPERATURE MUST BE IN K

21. Problems with Charles’ Law
TEMPERATURE MUST BE IN K!
Pressure is constant

22. THIRD LAW- RELATIONSHIP BETWEEN P AND T AT CONSTANT V
The pressure of a gas at constant volume is directly proportional to its K temperature

23. Review gas laws
The combined gas law

24. COMBINED GAS LAW
When no variable is kept constant.

26. Kinetic Theory of Gases
Ideal vs Real gases
Deviation from ideal behavior

27. Kinetic theory of gases (under ideal circumstances)
Gas are composed of particles that are in constant, rapid, random, linear motion.
Collisions between gas particles are elastic so no energy is lost. As a result, the pressure of a gas at a constant temperature and volume remains constant
The volume of the particles of a gas is so small compared to the distance between them, it is considered zero. The gas is mostly space.
There is no attraction or repulsion between gas molecules
The average kinetic energy of the molecules of a gas is directly proportional to the Kelvin temperature of the gas

28. Random : without definite aim, direction, rule, or method
Deviation : noticeable or marked departure from accepted norms of behavior
Random : without definite aim, direction, rule, or method

29. Ideal Gas Motion - at random Collision – cause pressure
Volume – insignificant
Attraction – no attractions

30. Deviations from ideal behavior
Particles of gas do have volume
Gas particles do attract each other
Optimum conditions
High temperature
Low pressure
Low molecular mass ( H2 and He are the lightest gases )

31. Real Gases Motion - at random Collision – cause pressure
Volume – can become significant
Attraction –weak attraction- but do exist