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Chemical Properties

(Section 2.3)

Chemical Properties  Ability of a substance to combine

with or change into new substances

  As a candle burns, the compounds (carbon and hydrogen) combine with oxygen in the air to form water and carbon dioxide

  The ability to burn is a chemical property

H20

H20 C02

02

C02

02 …CH2CH2…

Observing Chemical Properties

 Chemical properties can be observed only when the substances in a sample of matter are changing into different substances

Flammability  Is a material’s ability to burn in the

presence of oxygen  Materials that burn can be used as fuel  Some materials or fabrics are Flame-

resistant which means difficult to ignite

Reactivity

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Reactivity   Because Nitrogen has a

low reactivity it has many uses

  To prevent rust from forming in submarine tanks, nitrogen gas is pumped in to displace the oxygen gas to stop the reaction between the salt water and iron.

Recognizing Chemical Changes

  A chemical change occurs when a substance reacts and forms one or more new substances

  Examples   When a banana peel changes color   When a cake bakes in the oven   When leaves on trees change color   When food is digested in your stomach

Change In Color   Clue that a chemical change

has produced at least one new substance

  Examples   When silver becomes

tarnished (darker color because of a reaction to air)

  As a match burns it shrivels and becomes black

  Copper becomes greenish

Production of a Gas

  When you mix vinegar with baking soda bubbles of carbon dioxide form immediately

  When you use baking powder in a cake recipe the bubbles of carbon dioxide that form cause the cake to rise

Formation of a Precipitate   Any solid that forms

from a liquid mixture is called a precipitate

  When an acid is added to milk, proteins in the milk undergo a chemical change that alters their structure, causing them to stick together in clumps

Is a Change Chemical or Physical?

  When water boils it forms bubbles of gas but it is still water vapor

  When you heat iron it turns red but it is still iron   Ask yourself this question

  Are different substances present after the change takes place?

  When matter undergoes a chemical change, the composition of the matter changes

  When matter undergoes a physical change, the composition of the matter remains the same