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BELLWORK Element, compound, or mixture? Classify the following materials as an element compound or mixture. Give reasons for your answers . a.Table salt (NaCl) b.Salt water c.Apple juice
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Lecture 2.4- Chemical Changes

Nov 18, 2014

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Mary Beth Smith

Section 2.4 lecture for Honors & Prep Chemistry
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Page 1: Lecture 2.4- Chemical Changes

BELLWORKElement, compound, or mixture?

Classify the following materials as an element compound or mixture.

Give reasons for your answers.

a. Table salt (NaCl)

b. Salt water

c. Apple juice

d. Water (H2O)

e. Helium gas (He)

Page 2: Lecture 2.4- Chemical Changes

Lecture 2.4- Chemical changes

Page 3: Lecture 2.4- Chemical Changes

A magnet separates iron from sulfur.

During a physical change, the composition of matter never changes.

Physical Changes

Page 4: Lecture 2.4- Chemical Changes

Chemical Changes

A mixture of iron and sulfur is heated.

The iron and sulfur react and form iron sulfide.

During a chemical change, the composition of matter ALWAYS changes.

Page 5: Lecture 2.4- Chemical Changes

Recognizing Chemical Changes

It is usually a chemical change if there is :

Page 6: Lecture 2.4- Chemical Changes

Recognizing Chemical Changes

It is usually a chemical change if there is :•a transfer of energy (ex. heat or light)

Page 7: Lecture 2.4- Chemical Changes

Recognizing Chemical Changes

It is usually a chemical change if there is :•a transfer of energy (ex. heat or light)

•a change in color

Page 8: Lecture 2.4- Chemical Changes

Recognizing Chemical Changes

It is usually a chemical change if there is :•a transfer of energy (ex. heat or light)

•a change in color

•production of a gas

Page 9: Lecture 2.4- Chemical Changes

Recognizing Chemical Changes

It is usually a chemical change if there is :•a transfer of energy (ex. heat or light)

•a change in color

•production of a gas

• formation of a precipitate.

Page 10: Lecture 2.4- Chemical Changes

A precipitate is a solid that forms and settles out of a liquid mixture.

Page 11: Lecture 2.4- Chemical Changes

A chemical change is also called a chemical reaction.

Page 12: Lecture 2.4- Chemical Changes

A chemical change is also called a chemical reaction.

»A substance present at the start of the reaction is a reactant.

Page 13: Lecture 2.4- Chemical Changes

A chemical change is also called a chemical reaction.

»A substance present at the start of the reaction is a reactant.

»A new substance created by the reaction is a product.

Page 14: Lecture 2.4- Chemical Changes

A chemical change is also called a chemical reaction.

»A substance present at the start of the reaction is a reactant.

»A new substance created by the reaction is a product.

Fe + S FeSiron sulfur iron sulfide

Page 15: Lecture 2.4- Chemical Changes

A chemical change is also called a chemical reaction.

»A substance present at the start of the reaction is a reactant.

»A new substance created by the reaction is a product.

Fe + S FeSiron sulfur iron sulfide Reactants Product

Page 16: Lecture 2.4- Chemical Changes

Chemical Changes

The ability of a substance to undergo a specific chemical change is called a chemical property.

Page 17: Lecture 2.4- Chemical Changes

Chemical vs. Physical PropertiesQuickTime™ and a

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Page 18: Lecture 2.4- Chemical Changes

Conservation of Mass

LAW of Conservation of Mass–

During any chemical reaction, the mass of the products is always equal to the mass of the reactants.

Page 19: Lecture 2.4- Chemical Changes

The conservation of mass is easily observed when a change occurs in a closed container.

Page 20: Lecture 2.4- Chemical Changes

Conservation of Mass

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are needed to see this picture.