PHYSICAL AND CHEMICAL CHANGES

PHYSICAL AND CHEMICAL CHANGES

SECTION 15-4

A. PHYSICAL CHANGES

•A change that alters the form of a substance (physical properties), but does not change it to another substance

•Different states (solid, liquid, or gas), of the same matter

•CAN get it back

• PHYSICAL CHANGES CAUSE A CHANGE IN PHYSICAL PROPERTIES SUCH AS:

Size, Color, Shape, Density, Texture, Smell, or State

B. CHEMICAL CHANGES•Changed into a new substance with new properties. A new kind of matter!

•Bonds between atoms break, and the atoms rearrange to form new and different substances

•Also called a chemical reaction

•CANNOT get it back

•CLUES THAT A CHEMICAL CHANGE OR REACTION HAS OCCURED:

TEMPERATURE, LIGHT, SOUND, ODOR, FIZZING,COLOR CHANGE

absorbs energy releases energy absorbs energy

• Matter changes whenever energy is added or taken away• Thermal Energy – movement of particles

• heat particles – gain thermal energy• cool particles – lose thermal energy

• Chemical Energy – energy in chemical bonds• Break bonds – release energy• Form bonds – absorb energy

C. ENERGY

•LAW OF CONSERVATION OF ENERGY(applies to both chemical & physical changes)

Total amount of energy stays the same

Energy can change from one form to another, but energy is never lost or created

CONTROL THE RATE OF A CHEMICAL REACTION BY ADDING ENERGY OR

TAKING ENERGY AWAY

Why is meat stored in the freezer?

What happens to milk left on the counter?

Why do we place cake batter in an oven?

D. CHANGES IN STATES of MATTER

LIQUID

SOLID

GAS

VAPORIZATION(evaporization & boiling)

MELTINGFREEZING

CONDENSATION

Sublimation

Changing between Liquids & Solids• MELTING

• Change from a solid state to a liquid state• Melting Point - Temperature at which a

solid changes into a liquid• Matter absorbs thermal energy and the

temperature rises• FREEZING

• Change from a liquid state to a solid state• Freezing Point - Temperature at which a

liquid changes into a solid • Matter releases thermal energy and

temperature drops

Melting point and freezing point are the same for a given type of matter

Changing between Liquids & Gasses• VAPORIZATION

• Change from a liquid state to a gas state• EVAPORIZATION – vaporization that

takes place at the surface of a liquidExample - Puddle drying up after a rain shower

• BOILING – vaporization that takes place throughout the liquid (BOILING POINT)

• CONDENSATION• Change from a gas state to a liquid state• Gas particles cool, slow down enough to be

attracted to each other, and droplets form• Matter releases thermal energy

State Change Pyramid

Solid

Gas

Liquid

Melting

Freezing

Vaporization

Condensation

Subli

mation

Absorbingthermal energy

Releasingthermal energy

Why does sweating cool the human body? (hint: liquid changes state and uses thermal energy)

Why do liquids boil at a lower temperature in the mountains?(hint: boiling also depends on air pressure)

What state of matter are clouds, fog, & steam?(hint: water vapor is invisible)

Why do orange farmers in Florida spray their crops with water to save the oranges when a night freeze is predicted?(hint: liquid to solid, releases energy)

Directly from a Solid to a Gas• SUBLIMATION

• Change from a solid state to a gas state, without ever becoming a liquid

• Particles on the surface of a solid gain enough energy to become a gas

• Examples: dry ice (solid CO2) creates fog, snow seems to disappear

Graphing Changes of State

THERMAL energy- temperature changeCHEMICAL energy – no temperature change

(ALL horizontal areas are phase changes)