Kinetic Molecular Theory

Diffusion and Effusion

Gas Laws

3 Laws

Boyle's

Charles's

Avagadros's

Properties of a gas

Pressure (P)

Volume (V)

Temperature (T)

Moles (n)

Applying the Ideal Gas Law

Standard Conditions (STP)

1.0 atm, 273K

Standard Molar Volume

22.4 L (1 mol of gas at STP)

Gas doesn't matter

Gas Pressure

Created by gas molecules as they strike the surfaces around them.

Number of gas particles in a given volume (Concentration)

Volume of the container

Average speed of the gas particles (Temp)

**Gases**

Ideal Gas Law

By combing the gas laws we can write a general equation

Allows calculation of any variable if other 3 known

Density of a Gas

Density is ratio mass/volume

Density of a gas is generally given in g/L

Atmospheric Pressure

Differences in air pressure result in weather and wind patterns

The higher in the atmosphere you climb, the lower the atmospheric pressure.

at the surface the atmospheric pressure is 14.7 psi (1 atm), but at 10,000 ft it is only 10.0 psi

Barometer

ear popping

Wind

Breathing

Straws

Density

Collisions

Boyle's Law

Pressure

is inversely related to

Volume

Graph of P vs. 1/V is linear

P x V = constant

Charles's Law

Volume

is directly related to

Temperature

Graph of V vs. T is linear

V/T = constant (if T measured in Kelvin)

Avogadro's Law

Volume

directly proportional to the number of gas molecules (

Moles

)

V/n = constant

Equal volumes of gases contain equal numbers of molecules.

The gas doesn't matter

.

R

is called the

gas constant

Density at Standard Conditions

Density at Other Conditions

Density is directly proportional to molar mass

Easy to compare

Molar Mass of a Gas

One of the methods chemists use to determine the molar mass of an unknown substance is to heat a

weighed

sample until it becomes a gas; measure the temperature, pressure, and volume; and use the ideal gas law to calculate

moles of gas

.

What is different??

Combined Gas Law

Dynamic problems??

Practice Problem....

Procedure

1. Cancel out constant variables

2. Solve for unknown value

Dalton's Law of Partial Pressures

Each pressure value can be calculated using the ideal gas law

Mole Fractions can also be used

78%

21%

0.9%

Practice Problem???

The particles of the gas (either atoms or molecules) are constantly moving.

The attraction between particles is negligible.

When the moving gas particles hit another gas particle or the container, they do not stick;

elastic collision

.

There is a lot of empty space between the gas particles compared to the size of the particles.

The average kinetic energy of the particles is directly proportional to the Kelvin temperature

When gases are mixed together, their molecules behave independent of each other

All the gases have the same volume

fill the container

All gases at the same temperature

Same average kinetic energy

Can often be thought of as one gas

The pressure of a single gas in a mixture of gases is called its

partial pressure

The sum of the partial pressures equals the total pressure

For gases in reactions we use the ideal gas law...

to find moles of a component from P, V, and T.

to find Volume from moles of a component.

Stoichiometry of Gases

Simplest model for behavior of gases

Molecular Velocities

Since all the gas molecules in a sample can travel at different speeds we talk about the “average velocity” of the particles

however, the distribution of speeds follows a pattern called a Boltzman distribution

the method of choice for our average velocity is called the

root-mean-square

(u)

In a gas mixture at a given temperature lighter particles travel faster, on average, than heavier ones

KE directly proportional to Kelvin Temperature

The process of a collection of molecules spreading out from high concentration to low concentration is called

diffusion

.

The process by which a collection of molecules escapes through a small hole into a vacuum is called

effusion

.

Both rates are related to the average rms velocity

lighter gases both diffuse and effuse faster

Graham's law of Effusion