chapter 7. 10 chem

kinetic molecular theory

In this theory, a gas is modeled as a collection of particles (either molecules or atoms, depending on the gas) in constant motion.

kinetic molecular theory explains what

s explains the gas laws and some properties of liquids and solids.

gas laws explain what

the gas laws state mathematical relationships describing the behavior of gases.

Random motion

n means that gas particles travel in straight lines in any direction until they hit something.

perfectly elastic collision

means the particles bounce off one another without any loss of energy.

Five Postulates of the Kinetic Molecular Theory

1. Gases are composed of small molecules that are in constant, random motion.


2. The volume that is taken up by the molecules themselves is insignificant compared with the overall volume occupied by the gas.


3. Forces between the molecules are negligible, except when the molecules collide with one another.
4. Molecular collisions are perfectly elastic; that is, no energy is lost when the molecules collide.
5. The average kinetic energy of the gas molecules is directly proportional to the absolute temperature of the gas.

inelastic collision

do not bounce off each other, crash into each other, think car wreck

explain how gas pressure works

Postulates 1 and 3 state that gas particles are in constant motion and are colliding with each other.

The particles must also be colliding with the walls of their containers. The force of those collisions is source of gas pressure.

explain boyle’s law,

When the volume of this gas sample decreases, the rate of collisions of those particles with the container walls must increase.

The higher rate of collisions means higher pressure, so as volume decreases, pressure must increase

**Pressure and volume have an inverse relationship**

explain charles’s law

a gas sample is at a fixed pressure and number of particles, but in an expandable container at a certain temperature.

According to postulate 5 of kinetic molecular theory, an increase in temperature causes gas particles to have more energy and move at higher speeds.

• As these faster moving particles strike the walls of the container, they cause the container to expand, maintaining a constant pressure.

**Gas expands when heated**

explain Avogardo’s Law

• a gas sample is at a fixed pressure and temperature, but in an expandable container that allows you to add more moles of gas.

When the number of moles of gas are increased, the rate of collisions of those particles with the walls of the container increases.

As this greater number of particles strike the walls of the container, they cause the container to expand, maintaining a constant pressure.

\
 **the volume of any gas is proportional to the number of molecules of gas**

kinetic molecular theory formula

PV=nRT

• The pressure on a wall of a container occupied by particles in constant motion is the

e total force on the wall (due to the collisions) divided by the area of the wall.

average kinetic energy of the gas molecules depends on

average mass and velocity

Average kinetic energy of the gas formula

KEavg = ½NAmv^2

NA= avogardo’s number

m= mass

v= volume

gases in the same container have the same _______________t__herefore they have the same___________________ _____________ ___________

temperature;

same average kinetic energy

• If they have different masses, the only way for them to have the same kinetic energy is to have

different average velocities.

* –Lighter particles will have a faster average velocity than more massive particles

ideal gas law formula

KEavg = (3/2)RT

R= gas constant in energy units, 8.314 J/mol•K

1 J = 1 kg ∙ m2/s2

some formula idk

temperature vs. Molecular speed