MS-PS1-4: Thermal Energy and Phase Changes

MS-PS1-4
Thermal Energy and Phase Changes

Middle School

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Learning Objectives

• Predict how thermal energy changes a substance's particle motion, temperature, and state.

• Describe properties of solids, liquids, and gases based on their particle arrangement.

• Explain the difference between thermal energy, temperature, and heat.

• Explain how thermal energy transfer causes phase changes and thermal equilibrium.

• Describe the relationship between gas pressure, particle collisions, and phase changes.

Key Vocabulary

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Kinetic Energy

Kinetic energy is the energy of motion. Particles that are moving faster have more kinetic energy.

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Thermal Energy

Thermal energy is the total internal energy of a system, including both kinetic and potential energy.

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Heat

Heat is the transfer of thermal energy that occurs because of a difference in temperature.

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Pressure

Pressure is the force created by gas particles as they collide with the walls of their container.

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Equilibrium

Equilibrium is a state where energy transfer is balanced, resulting in a constant and stable temperature.

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Phase Change

A phase change is the process where matter transitions from one state to another, like solid to liquid.

Key Vocabulary

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Conduction

Conduction is the process of heat transferring between objects through direct contact of their particles.

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Melting

Melting is the phase change that occurs when a substance turns from a solid to a liquid.

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Freezing

Freezing is the phase change that occurs when a substance turns from a liquid to a solid.

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Evaporation

Evaporation is the phase change that happens when a substance turns from a liquid to a gas.

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Condensation

Condensation is the phase change that happens when a substance turns from a gas to a liquid.

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Sublimation

Sublimation is the unique phase change that occurs when a solid turns directly into a gas.

The Three Phases of Matter

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Solid

• A solid has a definite shape and a definite volume.

• Its atoms are very closely spaced together in a fixed pattern.

• The atoms vibrate in place but do not move around.

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Liquid

• A liquid has a definite volume but takes the container's shape.

• Its molecules are close but can move and slide past each other.

• This arrangement allows the liquid to flow easily from place to place.

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Gas

• A gas has no definite shape and no definite volume.

• Its molecules are widely spaced and move around freely and randomly.

• Gases can be compressed due to the large spaces between molecules.

Multiple Choice

Which statement correctly describes a solid?

• It has a definite shape and a definite volume.

• It takes the shape of its container but has a definite volume.

• It has no definite shape and no definite volume.

• Its atoms are widely spaced and move randomly.

Multiple Choice

What is the primary reason that liquids can flow and take the shape of their container?

• Their molecules can move and slide past one another.

• Their atoms are locked in a fixed, vibrating pattern.

• Their molecules are very far apart and move randomly.

• They have no definite volume and can expand infinitely.

Multiple Choice

A scientist has a sealed container of a substance. They are able to push the lid down, reducing the volume inside the container. Based on this action, what is the most likely state of the substance and why?

• Gas, because its molecules are widely spaced.

• Liquid, because its molecules can slide past each other.

• Solid, because its atoms vibrate in a fixed pattern.

• Gas, because it has a definite volume.

Temperature, Heat, and Thermal Energy

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Temperature

• ​Temperature is the average kinetic energy of particles in a substance.

• ​​It tells us how fast the particles are moving on average.

• ​It does not measure the total energy in the entire substance.

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Thermal Energy

• ​Thermal energy is the total energy of all particles in a substance.

• ​​This includes the kinetic energy from the movement of the particles.

• ​It also includes the potential energy stored within the particle bonds.

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Heat

• ​Heat is the transfer of thermal energy from one object to another.

• ​​This energy transfer occurs from a warmer substance to a cooler one.

• ​A difference in temperature causes this energy transfer to occur.

Multiple Choice

What does the temperature of a substance measure?

• The average kinetic energy of its particles.

• The total energy of all its particles.

• The transfer of energy between substances.

• The potential energy stored in its particle bonds.

Multiple Choice

What is the main difference between the thermal energy of a substance and its temperature?

• Thermal energy is the total energy of all particles, while temperature is the average kinetic energy of the particles.

• Temperature measures energy transfer, while thermal energy is the total energy of all particles.

• Thermal energy depends only on particle speed, while temperature depends on particle bonds.

• There is no difference; they are two words for the same concept.

Multiple Choice

If a cool metal spoon is placed into a cup of hot coffee, what process occurs?

• Thermal energy will be transferred from the hot coffee to the spoon.

• Thermal energy will be transferred from the spoon to the hot coffee.

• The temperature of the coffee will increase.

• The spoon's temperature will not change.

Kinetic Energy and Particle Motion

• Particles are always in motion and have kinetic energy.

• Heating increases kinetic energy, causing particles to expand.

• Cooling decreases kinetic energy, causing particles to contract.

Multiple Choice

What form of energy do particles have because they are always in motion?

• Kinetic energy

• Potential energy

• Chemical energy

• Nuclear energy

Multiple Choice

What is the relationship between heating a substance and the motion of its particles?

• Their kinetic energy increases, and they move farther apart.

• Their kinetic energy decreases, and they move closer together.

• Their kinetic energy stays the same, but they stop moving.

• Their size increases, but their kinetic energy is unchanged.

Multiple Choice

If a sealed, inflated balloon is placed in a freezer, it will shrink. Which statement best explains why this happens?

• The air particles inside the balloon lose kinetic energy and move closer together.

• The rubber of the balloon gets weaker and allows air to escape.

• The air particles inside the balloon gain kinetic energy and push less on the balloon.

• The cold air outside the balloon pushes harder on the balloon's surface.

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What Is Gas Pressure?

• Gas particles are always moving around randomly at high speeds.

• Pressure is the force from particles hitting the container walls.

• Adding heat makes particles move faster, increasing the pressure.

• Removing heat makes particles move slower, decreasing the pressure.

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Multiple Choice

What is gas pressure?

• The force from gas particles hitting the walls of a container.

• The total weight of all the gas particles in a container.

• The space that is occupied by gas particles.

• The random movement of gas particles at high speeds.

Multiple Choice

What is the relationship between adding heat to a gas and the pressure it exerts?

• It causes the particles to move faster, which increases the pressure.

• It causes the particles to move slower, which decreases the pressure.

• It causes the particles to stop moving, which eliminates the pressure.

• It does not change the speed of the particles or the pressure.

Multiple Choice

If a sealed container of gas is moved from a warm room into a cold freezer, what is the most likely outcome?

• The particles will move slower, causing the pressure to decrease.

• The particles will move faster, causing the pressure to increase.

• The particles will move slower, causing the pressure to increase.

• The particles will move faster, causing the pressure to decrease.

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Energy Transfer and Equilibrium

• Energy transfer through direct contact between particles is called conduction.

• Energy always transfers from hotter particles to colder ones.

• This continues until thermal equilibrium is reached and the temperature is stable.

• A thermometer shows temperature by reaching thermal equilibrium with the substance.

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Multiple Choice

What is conduction?

• Through direct contact between particles

• By creating light and sound waves

• By moving particles from one object to another

• Through empty space without touching

Multiple Choice

What happens when a hot object is in direct contact with a cold object?

• Energy flows from the hot object to the cold object until both are the same temperature.

• Energy flows from the cold object to the hot object, making the hot object hotter.

• The two objects exchange energy back and forth indefinitely.

• The temperature of both objects drops immediately.

Multiple Choice

When you place a thermometer in a cup of hot water, the reading rises and then stops. Which statement best explains why the reading stops changing?

• The thermometer has reached thermal equilibrium with the water.

• The thermometer has absorbed all the heat from the water.

• The water has cooled down to room temperature.

• The thermometer is broken and can no longer measure temperature.

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Understanding Phase Changes

Energy Added

• ​A phase change is a substance's transition from one state of matter to another.

• ​​Energy is added for melting (solid to liquid) and evaporation (liquid to gas).

• ​Sublimation also requires added energy for a solid to change directly into a gas.

Energy Removed

• ​A substance's temperature stays the same during any phase change until it is complete.

• ​​Energy is removed for freezing (liquid to solid) and condensation (gas to liquid).

• ​Deposition also requires removed energy for a gas to change directly into a solid.

Multiple Choice

What is a phase change?

• The transition of a substance from one state of matter to another.

• The process of changing a substance's color or shape.

• The time it takes for a substance to heat up.

• The creation of a new substance with different properties.

Multiple Choice

What is required for sublimation, the process of a solid changing directly into a gas, to occur?

• Energy is added to the substance.

• Energy is removed from the substance.

• The substance's temperature increases.

• The substance's temperature decreases.

Multiple Choice

If you place a cup of water in a freezer and watch it freeze, what would you observe about the water's temperature during the phase change?

• The temperature of the water will continue to drop as it freezes.

• The temperature of the water will stay the same until all of it has turned to ice.

• The temperature of the water will increase before it freezes.

• The temperature of the water will fluctuate up and down during freezing.

Pressure and Phase Changes

• Pressure can change the temperature at which substances change their state.

• Higher pressure makes it harder for a liquid to boil, increasing its boiling point.

• Lower pressure makes it easier for a liquid to boil, decreasing its boiling point.

Multiple Choice

What is the primary effect of pressure on a substance's phase change?

• It can alter the temperature at which a substance changes its state.

• It changes the chemical composition of the substance.

• It only affects the color of the substance.

• It increases the mass of the substance.

Multiple Choice

What is the relationship between increasing pressure and the boiling point of a liquid?

• The boiling point of the liquid will increase.

• The boiling point of the liquid will decrease.

• The boiling point of the liquid will stay the same.

• The liquid will turn into a solid immediately.

Multiple Choice

If you were trying to boil water at the top of a very high mountain, where air pressure is lower, what would you predict would happen?

• The water will boil at a lower temperature.

• The water will boil at a higher temperature.

• The water will take longer to freeze.

• The temperature for boiling will not change.

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Common Misconceptions

Misconception	Correction
Heating a substance makes its particles bigger.	Heating increases the space between particles, but the particle size remains the same.
Temperature and heat are the same thing.	Temperature measures particle energy; heat is the transfer of that energy.
During melting, temperature rises steadily.	Temperature stays constant during melting because energy is used to break bonds.

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Summary

• Particle arrangement and motion determine if matter is a solid, liquid, or gas.

• Temperature is the average kinetic energy of particles; heat is thermal energy transfer.

• Adding thermal energy causes expansion; removing it causes contraction.

• Gas pressure increases with temperature. Heat transfers until thermal equilibrium is reached.

• Temperature stays constant during a phase change, but pressure can alter this point.

Poll

On a scale of 1-4, how confident are you about predicting changes in particle motion, temperature, and state of matter?

• 1

• 2

• 3

• 4