Physical vs. Chemical ChangesNotes

We have discussed physical properties

that can be observed by using

our senses…

…and they can also be measured in

various ways.

shapeshape

Physical properties include…

colorcolorvolumevolume

massmassdensitydensitystatestate

temperaturetemperature

Changes in matter happen all the time. They can happen very quickly or slowlyover time.

Changes can be classified into two

types:

chemicalchemical

physicalphysical &&

A physical change occurs when the appearance of a substance changes…

…but chemicallychemically

the substance is still the

same.

The individual The individual molecules do molecules do not not changechange..

During some physical During some physical changes, matter changes, matter simply changes from simply changes from one one statestate to to anotheranother..

Evaporating, Evaporating, melting, freezing, melting, freezing, and condensing are and condensing are

examples of examples of physicalphysical changes.changes.

During some physical During some physical changes, an objects changes, an objects sizesize or or shapeshape may be may be alteredaltered……

For For example example folding or folding or tearing tearing paperpaper……

……or turning wood or turning wood into saw dust.into saw dust.

A physical change A physical change also occurs when also occurs when substances are substances are mixedmixed and and something something dissolvesdissolves……

In a physical In a physical change substances, change substances, like the water, keep like the water, keep their their original original propertiesproperties..

A chemical change A chemical change occurs when occurs when

chemical reactionschemical reactionstake place.take place.

Not only are the Not only are the mattermatter’’s s physicalphysical

properties changed, but properties changed, but it actually changes into it actually changes into

something new.something new.

EnergyEnergy is is involved in involved in

all all chemical chemical reactions.reactions.

The substances The substances produced during produced during a chemical a chemical reaction are reaction are differentdifferent from from the original the original substances with substances with new new propertiesproperties..

Signs that a Signs that a chemical chemical

reaction took reaction took place...place...

A solid A solid precipitate precipitate forms at forms at

the bottom the bottom of a test of a test

tube.tube.

Heat,Heat,smoke,smoke,

sound,sound, odor,odor,or or lightlight is is produced.produced.

A gas is A gas is produced produced causing causing

bubbling, bubbling, fizzing or fizzing or foaming.foaming.

A change in A change in temperature temperature

occurs.occurs.

A color change A color change occurs.occurs.

These These are only are only cluesclues……

……a chemical change a chemical change has not actually has not actually

taken place unless taken place unless mattermatter has changed has changed

into a into a new new substancesubstance..

Some common Some common examples of examples of

chemical chemical changeschangesincludeinclude……

RustingRusting……

TarnishingTarnishing……

BurningBurning……

CookingCooking……

DigestingDigesting……