Do Now:Do Now:1.1.What is KMT, What is KMT,

Kinetic Molecular Kinetic Molecular TheoryTheory

2.2.What are some What are some measurements we measurements we can take on a gas can take on a gas sample?sample?

Kinetic Molecular TheoryKinetic 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 neitherattractive nor repulsive forces on one another.• The average kinetic energy of the molecules is proportional to the temperature in Kelvin.

Measuring GasesMeasuring Gases• Amount – moles (n)

• Volume – dm3, Liters, mL, cm3 (V)•Temperature – Kelvin!!! (T)•Pressure – atm, mmHg, kPa, psi, others (P)Use barometer for atmospheric pressureUse manometer for gas pressure

What is STP? What is the significance?

• Standard atmospheric pressure is 760 mmHg (at 0 degrees C at sea level)

• It is dependent on elevation. At high elevation, air pressure is ____.

Atmospheric Pressure can be Atmospheric Pressure can be measured with a measured with a barometerbarometer

Manometers can be used to Manometers can be used to measure gas pressuremeasure gas pressure

Compare gas pressure to atmospheric pressure.

Gas Sample

Patm = 100.5 kPa

75 mm

Hg

Variables Equation Name of Law

P V

V T

P T

V n

P V T

P V T n

Gas Laws discovered by observation.Fill in table:

What does the term IDEAL signify in the ideal gas law?

Can also use ideal gas law Can also use ideal gas law to findto 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 To find molar mass, most likely collect gas over water:collect gas over water:

Gas Generation

Gas Collection

What will be impacted?

p.461 in your book

Dalton’s Law of Partial PressuresDalton’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 StoichiometryGas 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?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 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

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If the rms speed of He atoms in If the rms speed of He atoms in the exosphere (highest region the exosphere (highest region of the atmosphere) is 3.53x10of the atmosphere) is 3.53x1033 m/s, what is the temperature in m/s, what is the temperature in

Kelvin?Kelvin?

If I spray some perfume, it will If I spray some perfume, it will be a while until you smell it. be a while until you smell it.

Why?Why?

Mean free path – average distance particle travels between collisions

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

What is the effect of What is the effect of temperature on velocity?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. Compare an ideal gas vs. real gasreal gas

• Ideal gas – no interparticle interaction and zero volume for gas particles

• Real gas behaves ideally at ____ temperatures and ___pressures… why?

P = P = nRTnRT V V

P’ = nRT V –nbP’ (V –nb) = nRT

(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

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

Pobs = P’- n2a V2

Van der Waals equation

Although a and b are found experimentally, what do they correlate to?

Gases in AtmosphereGases in Atmosphere

• O3 unstable• absorbs energy, breaks

down to form O,O2

• O2 and O -> O3

Atmospheric PollutionAtmospheric Pollution

• 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.

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