Notes – Changes in States of Matter

Chapter 6, Lesson 2

Temperature, Thermal Energy, & Heat

• Changes in energy can cause matter to change from one state to another.

• A state change happens because of the change in motion of particles in an object.

Matter Changing State

Temperature, Thermal Energy, & Heat

• Even when an object is not moving, the particles in the object are moving.

• The particles have kinetic energy, which is energy of moving things.

The gas particles inside the balloon have energy because they are moving.

Temperature, Thermal Energy, & Heat

Temperature, Thermal Energy, & Heat

• Temperature is a measure of the average kinetic energy of the particles in a material.

• Particles in matter move faster as the temperature increases.

lower temperature higher temperature

Temperature, Thermal Energy, & Heat

• A thermometer is used to measure temperature.

• Particles in the thermometer’s gauge increase their speed when heated and start moving farther apart, causing the liquid in the thermometer to rise.

Temperature, Thermal Energy, & Heat

• Particles in a substance have potential energy.– Potential energy decreases as particles move

closer together.– Potential energy increases as particles move

farther apart.

Temperature, Thermal Energy, & Heat

Temperature, Thermal Energy, & Heat

• The total energy of the particles of a substance is its thermal energy.– Includes kinetic energy and potential energy

of a substance’s particles– A substance’s liquid state has more thermal

energy than its solid state– A substance’s gas state has more thermal

energy than its liquid or solid state.

Temperature, Thermal Energy, & Heat

• Heating adds thermal energy.

• Cooling removes thermal energy.

Temperature, Thermal Energy, & Heat

• When kinetic energy increases, the temperature of a substance increases.

• When potential energy increases, the substance changes state.

Melting

• solid → liquid

• Thermal energy is absorbed.

• Potential energy increases.

• Melting point is the temperature at which a material changes from solid to liquid.

Melting

• Thermal energy is added to a solid, & the temperature increases until the melting point is reached.

• The substance will not increase temperature until it has completely melted.

Melting

• The average kinetic energy does not change, only the potential energy changes.

• The attractive forces become weaker as particles increase speed and move farther apart.

Melting

Freezing

• liquid → solid

• Thermal energy is released.

• Potential energy decreases.

• Freezing point is the temperature at which a liquid changes to a solid.

Freezing

Vaporization

• liquid → gas

• Thermal energy is absorbed.

• Particles become too spread out and the attractive forces are too weak to keep the particles close together.

• Vaporization can occur both at the surface and inside the liquid.

Vaporization: Boiling

• Vaporization that occurs inside the liquid.

• Boiling point refers to the temperature that boiling occurs in a substance.

Vaporization: Boiling

Vaporization: Boiling

• The boiling point depends on the pressure exerted on the liquid.

• Bubbles in the liquid must form for boiling to occur.

• As air pressure increases, it becomes harder for the bubbles to form.

• The boiling point increases as air pressure increases.

Vaporization: Evaporation

• Evaporation is vaporization that occurs at the surface of a liquid.

• Evaporation occurs both at the boiling point and temperatures below the boiling point.

Vaporization: Evaporation

• The liquid gains thermal energy, and molecules on the surface gradually escape into the atmosphere

• (i.e.) water cycle, a puddle after rain, sweating to cool you down

Condensation

• gas → liquid

• Thermal energy is released.

• The gas particles slow down and move closer together until the attractive forces hold them together and a liquid forms.

Condensation

Sublimation

• solid → gas

• Thermal energy is absorbed.

• Bypasses liquid state completely.

• Dry ice (solid carbon dioxide) changes from a solid to a gas.

Deposition

• gas → solid

• Thermal energy is released.

• Bypasses liquid state completely.

• Water vapor changes directly to ice as frost on leaves.

Adding Thermal Energy

• The temperature of ice increases until the melting point is reached.

• The temperature stays constant as the ice melts.

Adding Thermal Energy

• After the ice has melted, the temperature increases until the boiling point is reached.

• The temperature stops increasing until all the water has changed to water vapor.

Adding Thermal Energy

• Adding more thermal energy causes the temperature of the water vapor to increase.

Removing Thermal Energy

• Water vapor changes back into ice by removing thermal energy.

Changes in Energy Among States of Matter

1. The point at which a liquid changes to a gas is called ____.

A melting point

B freezing point

C condensation point

D boiling point

6.2 Changes in States of Matter

2. A liquid can change to a gas through ____.

A evaporation

B freezing

C melting

D sublimation

6.2 Changes in States of Matter

3. Thermal energy must be ____ when a liquid changes to a ____.

A lost; gas

B gained; solid

C lost; solid

D increased; solid

6.2 Changes in States of Matter

4. Sublimation occurs when a solid changes into a ____.

A liquid

B gas

C plasma

D steam

5. As air pressure ____, the ____ of a liquid increases.

A decreases; boiling point

B decreases; freezing point

C increases; freezing point

D increases; boiling point

6. Adding thermal energy can ____ or ____.

A lower temperature; change the state of matter

B increase temperature; lower temperature

C increase temperature; change the state of matter

D remove kinetic energy; change the state of matter

SCI 3.e

7. One glass of water has a temperature of 30°C and another glass of water a temperature of 40°C. Which is true?

A The glass of water at 30°C has lower average kinetic energy.

B The glass of water at 40°C has lower average kinetic energy.

C The two glasses have equal average kinetic energy.

D none of the above

SCI 3.e