Physical vs. Chemical ChangesNotes

TEKS 6.5D identify the formation of a new substance by using the evidence of a possible chemical change such as production of a gas, change in temperature, production of a precipitate, or color change.

TEKS 8.5E investigate how evidence of chemical reactions indicate that new substances with different properties are formed.

Matter undergoes changes all of the time.

There are two types of changes:

chemicachemicall

physicalphysical &&

Physical changes:

Physical changes occur when the appearance of a substance changes…

…but chemicalchemical

lyly the substance is the same.

The The individual individual molecules molecules

do not do not changechange..

Examples of Examples of physical physical

changes are, changes are, melting, melting, freezing, freezing,

or changing or changing sizesize or or shapeshape..

A A physical physical change change

also also occurs occurs when when

substancsubstances are…es are…

mixedmixed and and something something dissolvesdissolves…like …like making salt water making salt water or Kool-aid.or Kool-aid.

The water, salt The water, salt and sugar still and sugar still keep their keep their original original propertiesproperties and and the the substances substances can be can be separated separated again.again.

Chemical Chemical ChangesChanges

A A chemical chemical changechange occurs occurs

when the when the atoms making atoms making

up matter up matter rearrangerearrange....

to form a new to form a new substance substance with with new new

propertiesproperties. .

This usually This usually occurs during occurs during

a a chemical chemical reactionreaction. .

Evidence of Evidence of a chemical a chemical

change:change:

ProductiProduction of a on of a gas.gas.

bubblesbubblesfizzingfizzing

foamingfoamingsmokesmokeodor odor

color changecolor change*not all color *not all color changes are changes are

chemical!chemical!

A A differentdifferent color appearscolor appears

*not all color *not all color changes are changes are

chemical!chemical!

FormatioFormation of a n of a

precipitatprecipitatee

cloudinescloudinesss

foggyfoggy

solidsolid at at bottom bottom of of containercontainer

Change in Change in heatheat or or

light light energyenergy

SparksSparksexplosionexplosionglowingglowing

temperatutemperature re

increases increases or or

decreasesdecreases

These These are are only only

cluesclues……

……a chemical a chemical change has not change has not actually taken actually taken place unless place unless matter has matter has

changed into a changed into a new substancenew substance..

Some Some common common

examples of examples of chemical chemical changeschanges

include…include…

RustingRusting……

Tarnishing…Tarnishing…

Burning…Burning…

Cooking…Cooking…

Digesting…Digesting…

If you have the If you have the chemical chemical

equationequation, you , you can tell if a can tell if a chemical chemical

change has change has taken place taken place

by…by…

Looking to Looking to see if the see if the

products in products in the equation the equation

are….are….

differentdifferent from from the the

reactantsreactants..