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EOG REVIEW 8 th grade SCIENCE

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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EOG REVIEW 8 th grade SCIENCE

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  1. EOG REVIEW 8th grade SCIENCE

  2. GOAL 4

  3. Unit D Chapter 3 pages D66 – D100 “Chemical Reactions”

  4. 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.

  5. A chemical change occurs when substances undergo a change that does alter their chemical nature. A chemical change involves a change in chemical properties.

  6. 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

  7. 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

  8. product a new substance formed by a chemical reaction; made by the rearrangement of atoms and bonds in reactants

  9. REACTANTS & PRODUCTS • can be elements or compounds • bonds between atoms • in the reactants are broken • and new bonds are formed • in the products

  10. 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

  11. EVIDENCE OF CHEMICAL REACTIONS 1) color change 2) formation of precipitate 3) formation of gas 4) temperature change

  12. precipitate a solid substance that forms as a result of a chemical reaction between chemicals in a solution

  13. exothermic reaction a chemical reaction that releases energy and gives off heat

  14. endothermic reaction a chemical reaction that absorbs energy

  15. 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)

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

  17. combustion reaction a reaction in which one reactant is always oxygen and another reactant often contains carbon and hydrogen EXAMPLE: burning

  18. CLASSIFICTIONS OF CHEMICAL REACTIONS 1) synthesis reaction N2 +3H2 2NH3 2) decomposition reaction 2H2 O2H2 + O2 3) combustion CH4 + 2O2 CO2 + 2H2 O

  19. 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

  20. chemical formula an expression that shows the number and types of atoms joined in a compound

  21. 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

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

  23. Balancing Equations Zn + 2HCl ---> ZnCl2 + H2 REACTANTS PRODUCTS ZnCl2 Zn 2HCl H2

  24. BALANCED EQUATIONS: Zn + 2HCl ---> ZnCl2 + H2 • (subscript = 2) • (coefficient = 2) 1 Zn 2H 2Cl = 1Zn 2Cl 2H WEBSITE: Balancing Act!

  25. 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

  26. 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

  27. THE END

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