Chapter 13: States of Matter Kinetic-Molecular Theory: Explains the motions and behavior of a gas. The theory has three components: 1. Particle Size: Gas.

Chapter 13: States of Matter

Kinetic-Molecular Theory: Explains the motions and behavior of a gas. The theory has three components:

1. Particle Size: Gas particles are small relative to the space around the particles. This means that there is no significant attraction or repulsion between gas particles. NO transfer of energy or elastic.

Kinetic Theory

2. Particle Motion: Gas particles are in constant and random motion.

a. Mean Straight Path: Gas particles move in a straight path until a collision.

b. Elastic collisions: collision between gas particles does NOT transfer energy. The total amount of kinetic energy of the two particles does not change.

Kinetic Theory

3. Particle Energy: defined by the mass and velocity of the gas particle.

a. Equation: KE = ½ mv2

KE = Kinetic energym = massv = velocity (both speed and direction)

• For a sample of the same gas, the masses will be the same but the velocity will differ.

• NOT all gas particles will have the same kinetic energy.

Kinetics Theory

b. Temperature: the average kinetic energy of a given sample of matter. OR ALL GASES HAVE THE SAME AVERAGE KINETIC ENERGY AT THE SAME TEMPERATURE.

Behavior of Gases:

Using the kinetic-molecular theory:

1. Low Density: D = m/v, a large volume like in a gas yields a small density

for equal mass. Compare a solid with a gas, the solid has more particles in

a given volume and therefore a greater density.

Behavior of Gases

2. Compression and Expansion. Gases fill the volume of the container, therefore the volume of the container defines the density of the gas. Distance between particles are large, therefore gases are very compressible.

Behavior of Gases

3. Diffusion: The flow of a gas into a space (already containing a gas).

• Rate of diffusion: depends on the mass of the gas. Lighter particles diffuse at a faster rate.

• At the same temperature, heavy and lighter gases must have the same average kinetic energy therefore lighter gases MUST be moving at a greater velocity.

Behavior of Gases

4. Effusion: the escape of gas through a tiny opening.

5. Diffusion: rate at which a molecules spreads out• Graham’s Law of Effusion: the rate of

effusion for a gas is inversely proportional to the square root of the molar mass.

• Equation

Example of Graham’s Law

The molar mass of helium is 4.0 g/mol. The molar mass of air is 29 g/mol. What is the ratio of diffusion rate? Which gas diffuses faster?

Samplers

1. Calculate the ratio of diffusion rates for neon and helium. Which gas diffuses faster? How much faster?

2. Calculate the ratio of diffusion for ammonia (NH3) and carbon dioxide (CO2). Which gas diffuses faster?

3. What is the ratio of diffusion rates for argon and radon? Which gas diffuses faster?

Gas Pressure

Pressure the force exerted per unit area.

1. atmospheric pressure: 1Kg/ cm2

**pressure decreases with an increase in altitude.

2. measured with a barometer (measures atmospheric pressure) or a

manometer (measures gas pressure in a closed container).

Gas Pressure

3. SI unit is pascal = 1 N/m2

4. conversions:

760 mm Hg = 760 torrs = 101.3 kPa = 1 atm at sea level.

Dalton’s Law of Partial Pressure

The total pressure exerted by gases within a container is the sum of pressure of all the gases in the container.

Ptotal = P1 + P2 + P3 ….

Example of Dalton’s Law

Air is made up of N2, O2, Ar, and CO2. Air pressure at sea level is 760 mm Hg. What is the pressure exerted by oxygen at sea level if N2 594 mm Hg, Ar 7.10 mm Hg and CO2 0.27 mm Hg?

Samplers

1. What is the partial pressure of oxygen gas in a mixture of nitrogen gas and oxygen gas if the total pressure is 0.48 atm and the particle pressure of nitrogen is 0.24 atm?

2. Find the total pressure of a mixture of gases with the following particle pressures: 6.6 kPa, 24 mm Hg and 1.2 kPa?

3. What is the total pressure of a mixture of gases with the following particle pressures: 58.6 torrs, 13.2 kPa, 2.43 kPa, 12.5 kPa, and 2500 Pa?

NOTE

Phase Changes

Solid, liquid and gas are the states or phases of matter.

1. The phase depends on the temperature (kinetic energy) and/or the pressure.

2. Note: figure 12-29, page 429.

3. Energy required to bring about phase change.

Energy Relationship in Phase Change

1. freezing point: temperature at which matter changes to a solid phase. Energy out.

a. normal freezing point: at STP (standard temperature and pressure, 1 atm @0oC).

2. melting point: temperature at which matter changes to a liquid.

Energy in.

Energy Related to Phase Change

1. vapor pressure: pressure at the surface of a liquid caused by the vaporization of the liquid. Energy in.

2. sublimation: solid changes to a gas with no liquid phase. Dry ice. Energy in.

3. deposition: gas changes to a solid with no liquid phase. Energy out.

4. vaporization: liquid changes to a gas or vapor usually with the in-put of energy. Boiling water. Energy in

Energy Related to Phase Change

evaporation: liquid changes to a gas only at the surface where the energy is high among to allow for the molecules to escape. The Sun heating and evaporating the surface of a lake. Energy in.

Phase Diagrams

Chart that shows the relationship between pressure and temperature as it pertains to changes in phase.

Be able to read and interrupt. Page 429.

Note: triple point: a temperature/pressure relationship in which matter exist in three phases.