1. Do Now: What is KMT, Kinetic Molecular Theory
What are some measurements we can take on a gas sample?

2. Kinetic Molecular Theory
Gas is composed of separate molecules that are very separated from one another. The molecules can be considered to be “points” with negligible volume.
Gas molecules are in constant, random motion and frequently collide with each other. Collisions among molecules are perfectly elastic.
Gas molecules exert neither
attractive nor repulsive forces
on one another.
The average kinetic energy
of the molecules is proportional
to the temperature in Kelvin.

3. Measuring Gases Amount – moles (n) Volume – dm3, Liters, mL, cm3 (V)
Temperature – Kelvin!!! (T)
Pressure – atm, mmHg, kPa, psi, others (P)
Use barometer for atmospheric pressure
Use manometer for gas pressure
What is STP? What is the significance?

4. Atmospheric Pressure can be measured with a barometer
Standard atmospheric pressure is 760 mmHg (at 0 degrees C at sea level)
It is dependent on elevation. At high elevation, air pressure is ____.

5. Manometers can be used to measure gas pressure
Gas Sample
Patm = kPa
75 mm Hg
Compare gas pressure to atmospheric pressure.

6. Gas Laws discovered by observation. Fill in table:
Variables
Equation
Name of Law
P V
V T
P T
V n
P V T
P V T n
What does the term IDEAL signify in the ideal gas law?

7. Can also use ideal gas law to find
Density of a gas. How? What measurements would need to be taken? What would you need to know about the gas - (not m and V)
Molar Mass of Gas. How? What measurements would need to be taken?

8. To find molar mass, most likely collect gas over water:
What will be impacted?
p.461 in your book
Gas Collection
Gas Generation

9. Dalton’s Law of Partial Pressures
For a mixture of gas in a container, the total pressure exerted in the sum of the pressures that each gas would exert if it were alone (partial pressures)
PT = P1 + P2 + ….Pn
Remember, volume of individual gas molecules insignificant

10. Gas Stoichiometry Gas laws pertain to gases!!!
A piece of sodium reacts with water. Write the reaction:
The hydrogen gas generated is collected over water at 25 degrees C. The volume of the gas is 246 mL measured at 1.00 atm. Calculate the number of grams of sodium used in the reaction. (Vapor pressure of water at 25 degrees C is atm)

11. How fast, on average, does a molecule move?
The average kinetic energy of the molecules is proportional to the temperature in Kelvin.
Any two gases at the same temperature will have the same average kinetic energy
KE = ½ mu2 and KE a T
KE = CT
KE = 3/2RT
NA (1/2 mu2) = 3/2RT
u2 = 3RT/M
Take square root, urms
-Mean square speed – Average of the square of the speeds of all molecules

12. If the rms speed of He atoms in the exosphere (highest region of the atmosphere) is 3.53x103 m/s, what is the temperature in Kelvin?

13. If I spray some perfume, it will be a while until you smell it. Why?
Mean free path – average distance particle travels between collisions

14. At STP, root mean square of oxygen is 500 m/s

15. What is the effect of temperature on velocity?

16. If two gases, A and B, are at the same temperature, how do their kinetic energies compare?
Graham’s Law
Can be used to describe diffusion and effusion of gases.

17. If it takes 10.6 hours for 1.00 L of nitrogen, N2, to effuse through the pores in a balloon, how long would it take for 1.00 L of helium, He, to effuse under the same conditions.

18. Compare an ideal gas vs. real gas
Ideal gas – no interparticle interaction and zero volume for gas particles
Real gas behaves ideally at ____ temperatures and ___pressures… why?

19. P = nRT V (Pobs + n2a) (V – nb) = nRT V2
P’ is corrected pressure by taking into account gas volume. Volume of real gas less than ideal because gas molecules take up space
P’ = nRT V –nb P’ (V –nb) = nRT
Pobs = P’- n2a V2
When gases are attracted, they will collide with less force, decreasing observed P. Correction depends on concentration, n/V. For interacting pairs, need to square that term. See p.209 for full description
Van der Waals equation
(Pobs + n2a) (V – nb) = nRT V2
Although a and b are found experimentally, what do they correlate to?

20. Gases in Atmosphere

21. O3 unstable
absorbs energy, breaks down to form O,O2
O2 and O -> O3

22. Atmospheric Pollution
Check out:
NOx ( from car and power plant emissions) produces ground level ozone and fine-particle pollution (smog)
SO2 (power plants and industry) reacts with O2 and H2O producing sulfuric acid – Acid rain
NO2 also produces acid rain. Acid rain destroys ecosystems and structures.