Molecular Motion and Temperature

People often think of temperature as how hot or cold something is. But what exactly is temperature?Temperature is a measure of kinetic energy. Every

substance is made up of particles. The temperature of a

substance is related to the kinetic energies of these

particles. If a substance is hot, its particles tend to have

a large amount of kinetic energy.

The particles in a substance have kinetic energy

because they are moving. The particles are constantly

in motion, even if the substance does not appear to be moving.

Select all of the statements that are true about

the rubber ball shown above.

• If the ball is cold, its particles tend to have a small amount of kinetic energy.

• The temperature of the ball depends on the kinetic energies of the particles that make up the ball

• The particles that make up the ball are moving even when the ball is not

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The kinetic energy of a ball or any other object depends on its mass and speed. The same is true of the kinetic energy of a particle.

The ___________ mass a particle has and the ________ the particle's speed, the more kinetic energy the particle has.

• less/higher

• more/higher

• less/lower

• more/lower

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Temperature is a measure of the kinetic energies of the particles in a substance. However, because the particles in a substance move at different speeds, the particles can have different amounts of kinetic energy. So, what does temperature actually measure?

Temperature measures the average kinetic energy of the particles in a substance. When the particles in a substance have a higher average kinetic energy, the substance has a higher temperature.

Imagine a substance made up of 1,000 particles. Which of these describes the average kinetic energy of the particles?

• the kinetic energies of the fastest particles multiplied by 1,000

• the sum of the particles kinetic energies divided by 1,000

• the total kinetic energies of the particle plus 1,000

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A substance has a higher temperature when its particles have a higher average kinetic energy.

Imagine two different substances that are both pure, meaning they each contain only one type of matter. Each substance has a different temperature.

Which two properties determine which substance has the higher temperature?

• the mass of one particle in each substance

• the kinetic energy of the fastest particle in each substance

• the mass of each substance

• the average speed of the particles in each substance

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Like all substances, gases are made up of moving particles.

The diagrams below show two pure samples of gas in identical closed containers. The colored balls represent the particles in each sample.

The mass of each particle is the same. The particles in sample A have a higher average speed than the particles in sample B.

Which particles have the higher average kinetic energy?

• the particles in sample A

• the particles in sample B

• neither; the average kinetic energy is the same

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The particles in sample A have a higher average kinetic energy than the particles in sample B.

Which sample has the higher temperature?

• Sample A

• Sample B

• The Temperature is the same

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Each particle in sample A has less mass than each particle in sample B. All of the particles are moving at the same average speed.

Which sample has the higher temperature?

• sample A; its particles have the higher average kinetic energy

• sample B; its particles have the higher average kinetic energy

• neither; the particles have the same average kinetic energy

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Imagine two pure samples of gas in identical closed containers: sample A and sample B. Sample A has a higher temperature than sample B.

Each of the statements below is true about the samples. Which statements describe a property that contributes to the difference in temperature? Select all that apply.

• The particles in Sample A have a higher average speed than the particles in sample B

• Each particle in sample A has more mass than each particle in sample B

• The total mass of sample A is higher than the total mass of sample B

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Think about what you've learned about how particle motion is related to temperature.

Select all of the statements that are true.

• How hot or cold a substance is depends on how fast its particles are moving

• If the particles in two pure substances have the same average speed, the substances must have the same temperature

• All the particles in a substance are moving at the same speed, and that speed determines the substance's temperature

• The total kinetic energy of the particles in a substance determines the substance's temperature

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Why does water NOT change temperature during boiling?

• Because the molecules of water take in all the heat to their nucleus
• Because heat is not the same thing as temperature
• Because adding heat doesn't ever change the temperature of water
• Because all of the energy is used to overcome the attraction of molecules

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