TOPIC: Heat AIM: How do

substances change from one phase to another?

States (phases) of matter • 1. SOLID • Molecules packed closely together • Vibrate in place

•Definite volume & shape

• 2. LIQUID • Molecules farther apart & move around

• Definite volume • No definite shape

• 3. GAS • Molecules very far apart & move around very fast • A lot of empty space (smaller density)

• No definite shape or volume

• 4. PLASMA • High energy molecules • Sun, stars, lightening, fluorescent & neon lights

Can you find the different phases of matter in this picture?

2 types of changes • 1. Physical change • Phase change • Does not produce a new substance • (change in appearance)

• Examples: freezing, melting, evaporation, tearing, crushing

• 2.

Chemical Change • Produces a NEW substance • Examples: burning, rusting

Paper  ash, smoke, heat

Iron + oxygen  iron oxide (rust)

Raw egg  cooked egg Cake batter  Cake

Sodium + Chlorine NaCl = Sodium Chloride (salt)

Phase change •Physical change •Requires heat energy

Phase Changes

Freezing •Liquid  Solid •Heat removed

Melting •Solid  Liquid •Heat added

Evaporation • Liquid  Gas • Heat added • Vaporization

Condensation •Gas  Liquid •Heat removed

•Opposite of evaporation

Sublimation • Solid  Gas • Heat added • Example: Dry ice (solid CO 2  gas)

Solid Gas

Gas Crystals

Example: Iodine crystals temp)  gas (slightly above room

Add heat



PHASE CHANGES Energy absorbed by molecules SOLID Melting S



L LIQUID Evaporation L



G GAS Freezing L



S Condensation G



L Remove heat



Energy released by molecules

Freezing point • Temp at which a liquid freezes (L  S) • FP of water = 0 ° C

Melting point • Temp at which a substance melts (S  L) • MP of water = 0 ° C

•Freezing Pt = Melting Pt

Boiling point • Temp at which a substance evaporates (L  G) • BP of water = 100 ° C

Evaporation occurs at the surface of a liquid (left). When a liquid boils, gas bubbles form throughout the liquid and then rise out of the liquid (right).

Temp of a substance during phase change • Stays the same until all of the substance has changed • Why? • Bc the energy is needed to change the substance, not the temperature

When water reaches its boiling point, it stays at 100°C until it all changes to steam. Them temperature of the steam can then rise above 100°C.

100°C T E M P 0°C PHASE CHANGE GRAPH FOR WATER Condensation Evaporation Boiling pt = 100°C Freezing Melting Time Freezing/melting point = 0 ° C

= phase changes

What is a mixture?

• 2 or more substances put together • No new substances • (not chemically combined) • Ex: salt water, salad…

• Can be separated • (Boiling, magnets, Filtering…)

What is a solution?

• Type of mixture • 1 substance dissolved in another

• 2 parts: • 1. Solute = what gets dissolved • 2. Solvent = what does the dissolving

•Example: Hot chocolate •Solvent = Water •Solute = Chocolate

Soluble • Able to dissolve • Ex: sugar is soluble in water

What affects the rate of dissolving?

• 1. Heat • (more heat  • 3. Stirring  dissolves faster) • 2. Surface area • (more surface area/smaller pieces dissolves faster)

Solubility • Max amount of substance that will dissolve in a certain amount of liquid

At 20 ° C, 38 grams of salt will dissolve in 100 grams of water. If more salt is added, it will not dissolve. It will sink to the bottom.

Greatest solubility

How does temp affect solubility?

• Temperature increases solubility

Solubility curves, like the one shown here, tell us what mass of solute will dissolve in 100g of water.