Changes of State

At its melting point, the particles of a solid substance are vibrating so fast that they break free from their fixed positions.

-At 0°C, the temperature of the ice stops increasing.The added energy (thermal energy) continues to change the arrangement of the water molecules from ice crystals into liquid water.The ice melts.

Melting Point

1) In most pure substances, meltibg occurs at a specific temperature. 2) Melting point is a characteristic property of a substance, chemists often compare melting points when trying to identify an unknown material. 3) The melting point of pure water is 0°C. 4) As a solid absorbs thermal energy, its molecules vibrate faster raising their temperature.

Sublimation

1) Occcurs when the surface particles of a solid gain enough energy to form a gas. 2)During sublimation, solids form a gas without passing through the liquid state. Example:Dry Ice (solid CO₂)

Condensation

1) The opposite of vaporization. 2) Condensation occurs when particles in a gas lose enough thermal energy to form a liquid. Example:1) Breath on mirror 2) Clouds 3) A "sweating" glass Clouds usually form when water vapor in the atmosphere condenses into liquid droplets.When the droplets get heavy enough, they fall to the ground as rain. Water vapor is a colorless gas that is impossible to see.The steam you see above a kettle of boiling water is not water vapor,and neither are clouds or fog.What you see in those cases are tiny droplets of liquid water suspended in air.

Boiling Point

1) The temperature at which a liquid boils. 2) Chemists use boiling point to help identify an unknown substance. (Chemists also use melting points for unknown substances.) The difference between boiling and evaporation is that during boiling, water vaporizes both at the surface and within the liquid.Whereas during evaporation , water vaporizes only at the surface.

Boiling

1) When vaporization occurs when a liquid changes to a gas below its surface as well as at the surface.Vaporization takes place throughout a liquid. 2) You see the results of this process when the boiling liquid bubbles.

1) The boiling point of a liquid also depends on the pressure of air above a liquid. 2) Lower air pressure, decreases (↓) the boiling point of a liquid.

3) Higher air pressure, increases (↑) the boiling point of a liquid. 4) The boiling point of water is 100°C.

Evaporation

A process when vaporizationtakes place only on the surface of a liquid. Example:A puddle of water on a sunny day.

During sublimation,particles of a solid do not pass through the liquid state as they form a gas.

Dry ice is solid CO₂ that changes directly into a gas.As it changes state, the CO₂ absorbs thermal energy.This is why dry ice is used to keep materials cold.

A substance changes state when its thermal energy increases or decreases sufficiently.

Examples:1) A liquid to gas-increase in thermal energy. 2) A solid to liquid-in crease on thermal energy. 3) A liquid to solid-decrease in thermal energy.

Solids that melt at temperatures that are higher room temperature (About 68°F=20°C) are plastic, candle wax, chocolate, butter (just to name a few).These materials becomea solid when they cool from a liquid state. Becoming a solid is the same as freezing, even when it occurs at room temperature.

How do particles in a solid substance change when energy is added? They vibrate faster. At what point do the particles of a solid break free from their fixed positions? At their melting point. Why do different substances have different melting points? They have different arrangements of particles that respond differently to added thermal energy.

The physical state of a substance is related to its thermal energy. Particles of a substance at a warner temperature have more thermal energy than particles of the same substances at a cooler temperature.

Particles of a liquid have more thermal energy than particles of the same substance in solid form. As a gas, the particles have even more thermal energy.

Vaporization

The change from a liquid to a gas.

Vaporization takes place when the particles in a liquid gain enough energy (thermal energy) to form a gas.

Two Types of Vaporization: 1)Evaporation 2) Boiling

Melting

the change in state from a solid to a liquid.

Freezing

the change of state from a liquid to a solid; the reverse of melting At its freezing temperature, the particles of a liquid are moving so slowly that they begin to form regular patterns.The liquid becomes a solid.