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EOG REVIEW 8 th grade SCIENCE

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EOG REVIEW 8 th grade SCIENCE. GOAL 4. Unit D Chapter 3 pages D66 – D100. “Chemical Reactions”. A physical change occurs when substances undergo a change that does not alter their chemical nature. A physical change involves a change in physical properties.

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Presentation Transcript
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EOG REVIEW

8th grade

SCIENCE

slide3

Unit D Chapter 3

pages D66 – D100

“Chemical Reactions”

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A physical change occurs when substances

undergo a change that does not alter

their chemical nature.

A physical change involves a change

in physical properties.

Physical properties can be observed without changing the type of matter.

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A chemical change occurs when substances

undergo a change that does alter

their chemical nature.

A chemical change involves a change

in chemical properties.

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chemical reaction

  • the process by which chemical changes occur and new substances are formed
  • atoms are rearranged
  • chemical bonds are broken and new bonds formed between different atoms
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reactant

a substance that is present

at the beginning

of a chemical reaction, takes part in the chemical reaction, and is changed into a new substance

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product

a new substance formed

by a chemical reaction;

made by the rearrangement

of atoms and bonds in reactants

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REACTANTS & PRODUCTS

  • can be elements or compounds
  • bonds between atoms
  • in the reactants are broken
  • and new bonds are formed
  • in the products
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Identify the reactants & the products-

1) Zn + 2HCl ZnCl2 + H2

REACTANTS

PRODUCTS

Zn

ZnCl2

2HCl

H2

2) CH4 + 2O2 CO2 + 2H2O

REACTANTS

PRODUCTS

CH4

CO2

2O2

2H2O

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EVIDENCE OF CHEMICAL REACTIONS

1) color change

2) formation of precipitate

3) formation of gas

4) temperature change

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precipitate

a solid substance that forms

as a result of a chemical reaction between chemicals

in a solution

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exothermic reaction

a chemical reaction that

releases energy and gives off heat

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endothermic reaction

a chemical reaction that

absorbs energy

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synthesis reaction

a reaction in which a

more complex substance

(a new compound)

is formed by the combination of

simpler reactants

(two or more elements or compounds)

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decomposition reaction

a reaction in which a compound (reactant) breaks down into simpler products, which could be elements or other compounds

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combustion reaction

a reaction in which one reactant

is always oxygen

and another reactant

often contains carbon and hydrogen

EXAMPLE: burning

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CLASSIFICTIONS OF CHEMICAL REACTIONS

1) synthesis reaction

N2 +3H2 2NH3

2) decomposition reaction

2H2 O2H2 + O2

3) combustion

CH4 + 2O2 CO2 + 2H2 O

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PG 79, 80,

Law of Conservation of Mass

  • a law stating that atoms are not created or destroyed in a chemical reaction
  • a law stating that the total mass of reactants is EQUAL to the total mass of products in a chemical reaction
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chemical formula

an expression that shows

the number and types of atoms joined in a compound

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subscript

a number written slightly below and to the right of

a chemical symbol that shows how many atoms of an element are in a compound

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coefficient

the number before a chemical formula that indicates how many molecules are involved in a chemical reaction

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Balancing Equations

Zn + 2HCl ---> ZnCl2 + H2

REACTANTS

PRODUCTS

ZnCl2

Zn

2HCl

H2

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BALANCED EQUATIONS:

Zn + 2HCl ---> ZnCl2 + H2

  • (subscript = 2)
  • (coefficient = 2)

1 Zn 2H 2Cl = 1Zn 2Cl 2H

WEBSITE: Balancing Act!

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PHYSICAL FACTORS CAN VARY

RATE of CHEMICAL REACTIONS

1) concentration- number of particles present in a certain volume

high concentration = faster reaction

2) surface area- breaking large piece

of material into smaller pieces increases

surface area

more surface area = faster reaction

3) temperature- adding heat energy

high temperature = faster reaction

TEXTBOOK- (pg D75) Particles and Reaction Rates

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CHEMICAL FACTORS CAN VARY

RATE of CHEMICAL REACTIONS

catalyst

a substance that

increases the rate

of a chemical reaction

but is not consumed in the reaction

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