Changes of State Lesson 14

Activator Why does ice cream melt? Thermal energy allows flow of heat from a warmer substance to a cooler substance Your ice cream absorbs thermal energy from the air and your hand Added energy changes the ice cream from a solid to a liquid

Changes between a Solid and Liquid How does the physical state of a substance relate to its thermal energy? Substance Liquid  more thermal energy Solid  less thermal energy Gas  most thermal energy Change from a solid to a liquid  increase in thermal energy Change from a liquid to solid  decrease in thermal energy

Melting Solid to liquid  melting In most pure substances, melting occurs at a certain temperature  melting point Melting point is a characteristic property

Melting How does an ice cube melt? Energy to melt ice cube comes from air Added thermal energy makes molecules vibrate  rises temp At the melting point, the particles are vibrating so fast that they break free from their fixed positions Ice cube melt

Imagine you are a particle of water in an ice cube Imagine you are a particle of water in an ice cube. Suddenly someone plonks you into a beaker and puts it over a Bunsen burner flame!! What would you experience next?? You are here Write a story, diary or design a cartoon strip to describe what is happening to you! Include as many of the words as you can from the box below!! Solid, liquid, gas, particles, heat energy, kinetic (movement) energy, bonds, melting, boiling

Freezing Changing from liquid to solid Freezing temperature  particles of a liquid are moving so slowly that they begin to form regular patterns Cold makes the particles lose thermal energy which causes them to move more and more slowly

Changes between Liquid and Gas Liquid to gas  vaporization Vaporization occurs when liquid particles gain enough energy to form a gas Two main types Evaporation Boiling

Liquid to Gas Evaporation: takes place only on the surface of a liquid Ex. Shrinking puddle Gains energy from the sun, air, ground Added energy allows surface particles to escape into the air

Liquid to Gas Boiling: liquids change to gas below and on surface Boiling causes bubbles Boiling point: temp at which a liquid boils Boiling point is used to help identify substances Depends on pressure of air above it Lower pressure  less energy required for liquid particles to escape

Condensation Opposite of vaporization Condensation: particles in a gas lose thermal energy to form a liquid Ex. Water vapor from a hot shower contacts the cool surface of the mirror and condenses into a liquid

Changes between Solid and Gas Sublimation: surface particles of solid gain enough energy to form a gas Particles do not pass through the liquid state Ex. Dry ice Solid carbon dioxide Cannot exist as a liquid, so instead of melting, it turns directly into gas