Unit 3 Kinetic Molecular Theory

Multiple Choice

Which among the following is NOT true regarding the Kinetic Molecular Theory of gases?

• Gases particles move in straight lines.

• Gas particles are closely packed and their motion is orderly.

• Gas particles are in constant motion.

• Gas particles do not attract or repel each other.

Multiple Choice

Which type of motion in the figure best represents the movement of gas particles?

• Motion 1

• Motion 2

• Motion 3

• Motion 4

Multiple Choice

Which of the following is true regarding the kinetic molecular theory of gases?

• Gas particles are attracted to one another.

• Gases consist of closely spaced particles.

• Gas particles move around in an orderly manner.

• The temperature of a gas depends on the average kinetic energy of the gas particles.

Multiple Choice

The pressure of each flask is given in atmospheres (atm). Flask 1 has the lowest pressure, and Flask 4 has the highest. Knowing what causes gas pressure, which of the following statements is true?

• Flask 1 contain the most molecules

• Flask 2 contain the most molecules

• Flask 3 contain the most molecules

• Flask 4 contain the most molecules

Multiple Choice

At what temperature do nitrogen molecules move fastest?

• 350 K
• 300 K
• 250 K
• 200 K

Multiple Choice

If you place a balloon in a freezer what happens to the size of the balloon?

• Doubles
• increases
• decreases
• stays still

Multiple Choice

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

• Collisions between gas particles are inelastic.

• Gases consist of closely spaced particles.

• Gas particles move around in an orderly manner.

• The temperature of a gas depends on the average kinetic energy of the gas particles.

Multiple Choice

Increasing the volume of a given amount of gas at constant temperature causes the pressure to decrease because __________________.

• the molecules are moving more slowly

• the molecules are moving more quickly

• the molecules are striking the container more frequently

• the molecules are striking the container less frequently

Multiple Choice

Why does the pressure inside a container of gas increase if more gas is added to the container at constant temperature?

• because there is a corresponding increase in the temperature

• because there is a corresponding decrease in volume

• because there is a corresponding increase in the force of the collisions between

  particles and the walls of the container

• because there is a corresponding increase in the number of particles striking an

  area of the wall of the container per unit time

Phase Changes

Phase changes are changes in the state of matter. For example: when a solid melts and becomes a liquid, that is a phase change.

What causes a phase change?

The single most important factor involving a phase change is heat.

Adding Heat

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Adding Heat

When heat is added to a substance, heat energy is absorbed by that substance.

That heat energy excites the particles.

Excited particles move faster, and the bonds between them break. This leads to a phase change.

Multiple Select

What phase change occurs with the addition of heat to a substance.

• Freezing

• Evaporation

• Melting

• Condensation

Adding Heat to a Solid - Melting

When heat is added to a solid, the particles are more excited, and the bonds between them are less rigid.

The particles can now move freely past one another.

The solid is now a liquid.

Adding Heat to a liquid - Evaporating

When heat is added to a liquid, the particles are more excited, and they move even further apart.

The particles now have a great amount of energy, can move at great speeds, and are farther apart.

Boiling vs. Evaporation.

Boiling occurs when all the molecules in a liquid have enough energy to vaporize.

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Evaporation occurs slowly, and only the molecules at the surface of the liquid contain enough energy to vaporize.

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Both boiling and evaporation are types of vaporization.

Multiple Choice

Can you skip the liquid state when adding heat?

Adding Heat to a solid - Sublimation

When enough heat is added to a solid substance, it can have enough energy to skip the liquid phase (melting), and vaporize directly into a gas.

A common example of this is dry ice, or solid Carbon Dioxide.

Melting and Evaporation are Endothermic.

Endo = into

Thermic = thermal or "heat"

Endothermic means putting heat into, or adding heat.

Removing Heat

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Removing Heat

When heat is removed from a substance, heat energy is take away from that substance.

When there is less energy in a substance, the particles slow down.

When particles slow down, they move closer together.

Removing Heat from a Gas - Condensation

When heat is removed from a gas, energy is taken away.

Less energy in gas = particles slow down.

When particles slow down, they move closer together, or condense.

This leads to the formation of water droplets.

Removing Heat from a Liquid - Freezing

When heat is removed from a liquid, energy is taken away.

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Less energy in liquid = particles slow down.

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When particles slow down, they move closer together, or freeze.

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This leads to the strong attraction of water molecules in ice, forming a rigid solid structure.

Removing Heat from a Liquid - Freezing

When heat is removed from a liquid, energy is taken away.

Less energy in liquid = particles slow down.

When particles slow down, they move closer together, or freeze.

This leads to the strong attraction of water molecules in ice, forming a rigid solid structure.

Multiple Choice

Can you skip the liquid state when adding heat?

Removing Heat from a gas - Deposition

When enough heat is removed from a solid substance, it can lose enough energy to skip the liquid phase (melting), and freeze directly into a solid.

A common example of this is when water vapor transforms directly into ice without becoming a liquid, a process that often occurs on windows during the winter months.

Key Points

Energy is required to change the phase of a substance, like the energy to break the bonds between molecules in a block of ice so it may melt.

During a phase change energy my be added or subtracted from a substance.

Particles change their position based on the amount of energy that is added, or removed. The change in position results in a phase change.

Your Assignment

Copy down and fill out the graph in the next slide using this Quizizz lesson. When finished, take a picture, and upload it to Google Classroom under this assignment. Turn it in.