1. NOTES: 13.1 & 14.1 Gases and Kinetic Molecular Theory

2. Gases doing all of these things!
BEHAVIOR OF GASES
● Gases have weight
● Gases take up space
● Gases exert pressure
Gases doing all of these things!

3. All gases have the following PHYSICAL characteristics:
Gases assume the volume and shape of their containers.
Gases are the most compressible of the states of matter.

4. All gases have the following PHYSICAL characteristics:
Gases will mix evenly and completely when confined to the same container.
Gases have much lower densities than liquids and solids.

5. States of Matter: Property Solid (s) Liquid (l) Gas (g) Shape Definite
Indefinite
Volume
Expansion Upon Heating
Very slight
Slight
Great
Distance Between Molecules
Very Close
Close
Compressibility
Poor

6. Kinetic Molecular Theory:
The behavior of matter in its different states can be explained using Kinetic Molecular Theory.
Kinetic Molecular Theory – a theory explaining the states of matter based on the concept that the particles in all forms of matter are in constant motion
KINETIC ENERGY = energy an object has due to its motion

8. Kinetic Theory of Gases:
In gases, Kinetic Molecular Theory depends on the
following assumptions: (gas is behaving “ideally”)
● Gaseous matter is composed of small, hard spheres that have insignificant volume and are far apart from each other.
● There is so much empty space between particles, they are assumed neither to attract nor to repel each other.

9. Kinetic Theory of Gases:
● Particles move rapidly and in constant random motion. (straight paths independent of other molecules)
● All collisions are perfectly “elastic.” (kinetic energy is conserved)
**Real gases do not conform to these assumptions!

11. Kinetic Energy and Kelvin Temperature:
● As particles are heated they absorb energy, thus increasing their average kinetic energy and their temperature
● Molecules at a specific temperature have a wide range of kinetic energies

12. Kinetic Energy and Kelvin Temperature:
● Theoretically, molecular motion stops at absolute zero (0 Kelvin)
● Kelvin temperature scale reflects the relationship between temperature and average kinetic energy
● Kelvin temperature scale is directly proportional to the average kinetic energy

13. Ideal Gases:
● We define an ideal gas as a “hypothetical” gas that conforms to the assumptions of the kinetic gas theory.
● “Real” gases typically exhibit behavior that is closest to “ideal” behavior at low pressure and high temperature.
● typically, we assume conditions are “standard”
● STP = standard temperature and pressure
= 0ºC (273 K) and 1 atm

14. Measurements of Gases:
● To describe a gas, its volume, amount, temperature, and pressure are measured.
 VOLUME (V):
measured in L, mL, cm3 (1 mL = 1 cm3)

15. Measurements of Gases:
 AMOUNT: measured in moles (n),
or grams (which can be converted to moles using molar mass)

16. Measurements of Gases:
 TEMPERATURE: measured in KELVIN (K)
K = ºC + 273

17. Measurements of Gases:
 PRESSURE:
measured in mm Hg, torr, atm, Pa, kPa

18. Gas Pressure: ● PRESSURE = force exerted per unit area (force/area)
● In a gas, pressure is a result of molecular collisions
● Can be measured using a barometer or manometer

19. P = F /A Moderate Force (about 100 lbs) Small Area (0.0625 in2)
Enormous Pressure (1600 psi)

20. Bed of Nails Small Pressure P = F / A Moderate Force
Large Surface Area
(lots of nails)

21. Units of Pressure: ● Units of Pressure: 1 atm = 760 mm Hg
1 atm = 760 torr
1 atm = x 105 Pa
1 atm = kPa
1 atm = bar

22. Factors Affecting Gas Pressure:
**using kinetic theory, we can predict and explain how gases will respond to a change of conditions
**the factors affecting gas pressure are:
-amount of gas
-volume
-temperature

23. Amount of Gas: ● when you add gas to a container:
-the # of particles increases
-the # of collisions between particles increases
-the pressure increases

24. Amount of Gas: ● when you remove or release gas from a container:
-the # of particles decreases
-the # of collisions between particles decreases
-the pressure decreases

25. Amount of Gas: **the relationship is direct:
-if you double the amount of gas: pressure doubles;
-if you triple the amount of gas: pressure triples;
-etc.

26. Amount of Gas:
● when a sealed container of gas under pressure is opened:
-gas moves from an area of
high pressure to an area
of low pressure
-example: a can of spray paint

27. VOLUME: ● when you decrease the volume of a container of gas:
-the gas becomes compressed;
-the pressure increases.
**if you reduce the volume
by ½ , you double the
pressure

29. VOLUME: ● when you increase the volume of a container of gas:
-the gas becomes more “spread out”;
-the pressure decreases.
**if you increase the volume by 2, the pressure decreases by ½ .

30. TEMPERATURE: ● when the temperature of a container of gas increases:
-the speed and K.E. of the gas particles increases;
-the # of collisions between gas particles increases;
-the pressure increases
**if you double the temperature (in KELVIN), the average KINETIC ENERGY of the particles doubles, and the pressure doubles.

31. TEMPERATURE: ● when the temperature of a container of gas decreases:
-the speed and K.E. of the gas particles decreases;
-the # of collisions between gas particles decreases;
-the pressure decreases
**if the Kelvin temp. is reduced by ½, the pressure is reduced by ½.

32. Okie Dokie
Lets play with gases.