Notes – Changes in States of Matter Chapter 6, Lesson 2.
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Transcript of 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 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
• 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.
Freezing
• liquid → solid
• Thermal energy is released.
• Potential energy decreases.
• Freezing point is the temperature at which a liquid changes to a solid.
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
• 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.
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.
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
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