10.1 Kinetic-Molecular Theory of Matter

How does the kinetic-molecular theory of matter explain the properties of matter?

SC.912.P.8.1 Differentiate among the four states of matter.

SC.912.P.10.5 Relate temperature to average molecular

kinetic energy. SC.912.P.12.10

Interpret the behavior of ideal gasses in terms of kinetic molecular theory.

Temperature - the measure of average kinetic energy (KE) of a gas, liquid, or solid.

Kinetic energy is the energy of motion. Temperature is directly related to the

number of particle collisions. The amount of KE of matter determines

the state of matter it takes.

The Kinetic-Molecular Theory of Matter States that particles of matter are always in

motion. Can be used to explain the properties of

solids, liquids, and gasses in terms of energy of particles and the forces that act between them.

Kinetic-Molecular Theory and Temperature

Gasses: Ideal gas: a hypothetical gas that perfectly

fits the assumptions of the kinetic molecular theory

5 assumptions of kinetic-molecular theory of gasses:

1. Gasses consist of large numbers of tiny particles that are far apart in relation to their size.

The volume of a gas is about 1000 x greater than the volume of a liquid or a solid with just as many particles.

2. Collisions between gas particles and container walls are elastic collisions.

Elastic collisions are ones where there is no net loss of energy.

Kinetic energy is transferred between two particles during collisions and no energy is lost.

3. Gas particles are in continuous, rapid, random motion.

This motion is a form of kinetic energy.

The energy helps the particles overcome the attractive forces between particles.

4. There are no force attractions between gas particles.

When gas particles collide, they do not stick together. They immediately bounce apart.

5. Temperature of a gas depends on the average amount of kinetic energy of the particles of gas.

Which of the following is not true about the volume of a gas?

A. Most of the volume is empty space.B. The volume is occupied by particles in

continuous, rapid, random motion.C. The volume is about 10 times greater

than that occupied by an equal number of particles in the liquid or solid state.

D. Generally, the volume can be easily changed

Which of the following is an assumption of the kinetic-molecular theory of gases?

A. Gases consist of closely spaced particles.B. Collisions between gas particles are

inelastic.C. Gas particles move around in an orderly

manner.D. The temperature of a gas depends on

the average kinetic energy of the gas particles.

KE = ½ MV2

M = mass of the particleV = it’s velocity (speed)

Average speeds and kinetic energy of the particles increases and decreases with temperature.

Because all gasses at the same temperature have the same KE, it means that lighter gasses move faster than heavier gasses at the same temperature.

If a gas has the same temperature throughout, which gas molecule has the highest average velocity?

A. O2

B. H2O

C. H2

D. Xe

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Kinetic-molecular theory applies ONLY to ideal gasses.

Ideal gasses do not exist. However, some gasses exhibit near ideal

gas behavior under certain conditions. Therefor, K-M Theory can account for

many observed properties of gasses.

Properties of Gasses:1. Expansion:

Gasses have no definite shape, no definite volume

Gasses completely fill a container and take it’s shape

A gas transferred from a 1 L vessel to a 2 L vessel will expand to take up all the space.

2. Fluidity: Because the attractive forces between particles

are insignificant, the particles easily glide past one another, like the particles of a liquid.

This is why gasses and liquids are referred to as fluids.

3. Low Density: Density of gasses at normal atmospheric

pressure are about 1/1000 the density of it’s liquid or solid counterparts because the particles are much farther apart.

4. Compressibility: The volume of a gas can be greatly decreased by

putting it under pressure. Under compression, the particles of a gas are

much closer together. This increases the number of particle collisions

and therefor the temperature.

5. Diffusion and Effusion: Gasses spread out and mix with one another. Air freshener sprayed in the front of the room will

diffuse throughout the entire room within minutes. Diffusion- spontaneous mixing of particles of a

gas caused by the random motion of the particles.

Effusion is the process by which gas particles pass through a small opening. Effusion rates are directly proportional the speed of

the particles. Therefor, small molecules effuse more readily than

larger particles.

Diffusion and Effusion

Properties of Gasses

Because particles of gasses occupy space and exert attractive forces on each other, ideal gasses do not exist.

A real gas is a gas that does not behave completely according to the assumptions of K-M theory.

Real gasses behave most like ideal gasses under low pressure and high temperature (which gives them space and energy to move).

Nobel gasses show idealistic gas behavior due to the small attractive forces between particles (full octet).

Diatomic molecules (O2, N2, H2, I2, etc.) show the most ideal behavior. This is because they are nonpolar molecules (the electronegativity difference between atoms is 0).

The more polar a gas molecule is, the less ideal behavior it will exhibit due to polar attractive forces between molecules.

Comparing Real and Ideal Gasses

Rates of effusion of different gases are proportional to their

A. particle velocities.B. polarity.C. particle charge.D. compressibility.

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A hypothetical gas that perfectly fits all the assumptions of the kineticmolecular theory is known

as

A. A real gasB. An ideal gasC. An imaginary gasD. A perfect gas

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Which gas deviates the most from ideal behavior?

A. Cl2B. COC. NeD. He

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