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

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.

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?

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 ____.

Manometers can be used to measure gas pressure Gas Sample Patm = 100.5 kPa 75 mm Hg Compare gas pressure to atmospheric pressure.

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?

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?

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

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

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 0.0313 atm)

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 https://www.khanacademy.org/science/physics/thermodynamics/laws-of-thermodynamics/v/proof-u-3-2-pv-or-u-3-2-nrt

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?

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

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

What is the effect of temperature on velocity?

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.

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.

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?

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?

Gases in Atmosphere

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

Atmospheric Pollution Check out: http://www.epa.gov/air/urbanair/ 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.