Regents Chemistry

11/9/2008Mrs. Nephew

Kinetic Molecular Theory

Describes why gases behave the way they do.

Major ideas of K.M.T.

1. Gases contain particles (usually molecules or atoms) that are in constant, random, straight-line motion.

Major ideas of K.M.T.

2. Gas particles collide with each other and with the walls of the container. Collisions may result in transfer of energy among particles, but there is no net loss of energy. Collisions are said to be perfectly elastic.

Elastic Collision

Collison in which the KE of both objects is conserved.

Major ideas of K.M.T.

3. Gas particles are separated by relatively great distances. (So the volume occupied is negligible andΩ need not be accounted for).

Major ideas of K.M.T.

4. Gas particles do not attract each other.

Relationships of the K.M.T.

Pressure and Numbers of Gas Particles

Gases exert pressure because their molecules collide with each other and with the walls of their container.

The greater the number of air particles, the greater the pressure. (Directly proportional).

(Think bike tire and inflation….).

Relationships of the K.M.T.

Pressure and Volume of a Gas

Volume and pressure are inversely related. Increase pressure and volume decreases and vice versa. (i.e. If you push the lid on a container down, the particles hit the wall of the container more often-pressure increased and volume is now less). END-11/10/08

Relationships of the K.M.T.

Relationship of temperature and pressure of a gas

Temp rises, KE increases. Increase in velocity of particles. Causes the particles to hit the walls of the container more often and with greater force.

SO an increase in temperature causes the pressure to increase.

Relationships of the K.M.T.

Relationship of temperature and volume of a gas

As temperature increases, molecules push harder on the container. Increases pressure, so volume increases.

Relationships of the K.M.T.

Relationship of temperature and velocity

Temperature increases, the kinetic energy increases. This is caused by the greater average velocity of the particles.

Combined Gas Law Equation

Illustrates the relationship between all the variables we’ve just discussed.

If a variable remains constant, you can just cross it out and use the remaining two.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

STP???

Standard temperature and pressure is defined as one atmosphere of pressure and a temperature of 0 C (273K).

Pressure is defined as force per unit area. Often expressd in units of torr, mm Hg, atm

and kPa. Normal atmospheric pressure is 760 torr, 760

mm Hg, 1 atm and 101.3 kPa.

Ideal Gas-a collection of particles that:-have mass but negligible volume-Move randomly in straight lines-Are not subject to any attractive or

repulsive forces (except during collisions with each other or walls of their container)

-Collide in a perfectly elastic fashion, no energy is lost during collision.

KMT model enables us to draw 3 conclusionsVolume occupied by an ideal gas is

essentially the volume of its container.Pressure exerted by an ideal gas is

related to number of collisions that particles make with the walls of the container in a given amount of time.

Absolute (K) temperature of an ideal gas is directly proportional to the avg. KE of the gas particles.

Studying Gases

We assume they behave ideally.

Ideal Versus Real Gases

Ideal gas model does not exactly match behavior of real gases.

Two Assumptions of K.M.T. that aren’t exactly correct: Gas particles do not attract one another.

(usually attractive forces are so small it they can be disregarded, but under extreme conditions those small forces become important).

Gas particles do not occupy volume. (As pressure increases, can’t deny particle volume, collisons are more likely and particles have greater chance of combining).

Gas is ideal if:

It behaves exactly as predicted.Gases are most ideal at low pressures

and high temperatures.Hydrogen and Helium are nearly “ideal”

in behavior, but no gases are truly ideal.

Inc. mass and inc. polarity cause gases to vary from ideal behavior.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Separation of Mixtures

Filtration-can be used to separate a solid from a liquid.-substance that passes through the filter is called the filtrate. The substance remaining on the filter is called the residue.-can separate solids and gases.(cars, trucks, air conditioners)

Two liquids that are not soluble in each other are called immiscible.(oil and water).Can use separatory funnel for those types.

DistillationA technique that can be used to physically separate most homogeneous mixtures based on the differences in the boiling points of the substances involved.

Es. Gasoline is obtained from crude oil by the process of distillation.

ChromatographyA technique that is used to separate the

components of a mixture based on the tendency of each component to travel or be drawn across the surface of another material.

http://www.youtube.com/watch?v=kz_egMtdnL4