Kinetic Theory of Matter

Kinetic Theory of Matter

Middle School

​

Learning Objectives

• Define kinetic energy and the kinetic theory of matter.

• Describe the properties of solids, liquids, and gases.

• Explain how the kinetic energy of particles determines the state of matter.

• Compare the particle motion in solids, liquids, and gases.

Key Vocabulary

​

Kinetic Energy

Kinetic energy is the energy of moving matter. All particles that make up matter have it.

​

Kinetic Theory of Matter

This theory states that all matter is made of particles that are always in constant motion.

​

Solid

A state of matter that maintains a fixed shape and also has a fixed, unchanging volume.

​

Liquid

A state of matter that has a fixed volume but takes the shape of its container.

​

Gas

A state of matter that does not have a fixed shape or a fixed, constant volume.

What Are the States of Matter?

​

Solids

• ​Solids have a fixed shape and a fixed volume.

• ​​The particles in a solid are packed tightly together.

• ​They are held rigidly in place and can only vibrate.

​

Liquids

• ​Liquids have a fixed volume but can change their shape.

• ​​The particles in a liquid can slide past one another.

• ​They cannot pull apart from each other completely.

​

Gases

• ​Gases have neither a fixed shape nor a fixed volume.

• ​​The particles in a gas can pull far apart.

• ​They spread out to fill the entire container.

Multiple Choice

A substance has a fixed volume but changes shape when poured into a new container. What is its state of matter?

• Liquid

• It could be a solid or a liquid.

• Gas

• Solid

​

​

Energy and the Kinetic Theory

• Energy is the ability to cause changes in matter or to do work.

• Kinetic energy is the specific type of energy associated with moving matter.

• The tiny particles that make up all matter are in constant, random motion.

• The kinetic theory of matter explains the properties of solids, liquids, and gases.

​

Multiple Choice

What is the core idea of the kinetic theory of matter?

• Kinetic energy only exists in hot objects.

• All matter is made of stationary particles.

• All matter consists of particles that are in constant motion.

• Only gas particles are in motion.

Kinetic Energy vs. Forces of Attraction

​

Solids

• ​Particles have low kinetic energy and strong forces of attraction.

• ​​Energy cannot overcome the attractions holding particles rigidly in place.

• ​The particles are only able to vibrate in fixed positions.

​

Liquids

• ​Particles have enough kinetic energy to partially overcome attractions.

• ​​They are still close together but are not fixed.

• ​This allows the particles to slide freely past one another.

​

Gases

• ​Particles have high kinetic energy that overcomes forces of attraction.

• ​​There is a great deal of space between the particles.

• ​This allows them to pull far apart and spread out.

Multiple Choice

In which state of matter does the kinetic energy of particles largely overcome the forces of attraction between them, allowing them to spread out?

• Solid

• Gas

• Liquid

• Solid and Liquid

​

Common Misconceptions about States of Matter

Misconception	Correction
Particles in a solid are completely still.	Solid particles are always in motion, vibrating in fixed positions.
The state of matter depends only on temperature.	The state depends on kinetic energy and forces of attraction.
Gas particles have no attraction to each other.	They have weak attraction, but high kinetic energy overcomes it.

Multiple Choice

How does the kinetic theory of matter explain why a liquid takes the shape of its container but a solid does not?

• Liquid particles have no forces of attraction between them.

• Solids are always denser than liquids.

• Liquid particles have enough kinetic energy to slide past each other, while solid particles can only vibrate in place.

• Solid particles have more kinetic energy than liquid particles.

Multiple Choice

If you significantly decrease the kinetic energy of particles in a gas, what change of state is most likely to occur and why?

• The gas will expand because the particles are moving less.

• The gas will become a liquid because forces of attraction will pull the slower-moving particles together.

• The state will not change, only the pressure will decrease.

• The gas will become a solid because the particles stop moving completely.

Multiple Choice

A puddle of water disappears from the sidewalk on a sunny day. Using the kinetic theory, predict what happened to the water particles.

• The particles were absorbed by the concrete and became a solid.

• The particles simply moved to another location on the sidewalk as a liquid.

• The sun's energy increased the particles' kinetic energy until they overcame attractive forces and escaped as a gas.

• The sun's energy decreased the particles' kinetic energy, causing them to freeze.

Multiple Choice

The fizz in cola is dissolved carbon dioxide (CO₂), a gas. Analyze what happens in terms of kinetic energy and forces when you shake a can and open it.

• Shaking turns the liquid cola into a gas, which pushes the CO₂ out.

• Shaking increases the CO₂ particles' kinetic energy, allowing them to overcome attractions, form a gas, and expand rapidly.

• Opening the can reduces the forces of attraction between all particles.

• Shaking decreases the kinetic energy of the CO₂, forcing it out of the liquid.

​

Summary

• All matter is made of tiny particles that are always in constant motion.

• The state of matter depends on the particle's energy and the forces between them.

• In solids, particles have low energy and vibrate. In liquids, they have more and slide.

• In gases, particles have the most energy, moving far apart to fill their container.

Poll

On a scale of 1-4, how confident are you about the Kinetic Theory of Matter?

• 1

• 2

• 3

• 4