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Chemical Changes

Chemical Changes. Chapter 21.1 & 21.2. SC Standards Covered. Standard PS-4.7 Summarize characteristics of balanced chemical equations (including conservation of mass and changes in energy in the form of heat—that is, exothermic or endothermic reactions). Standard PS-4.8

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Chemical Changes

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  1. Chemical Changes Chapter 21.1 & 21.2

  2. SC Standards Covered • Standard PS-4.7 • Summarize characteristics of balanced chemical equations (including conservation of mass and changes in energy in the form of heat—that is, exothermic or endothermic reactions). • Standard PS-4.8 • Summarize evidence (including the evolution of gas; the formation of a precipitate; and/or changes in temperature, color, and/or odor) that a chemical reaction has occurred.

  3. Standard PS-4.9 • Apply a procedure to balance equations for a simple synthesis or decomposition reaction. • Standard PS-4.11 • Recognize simple chemical equations (including single replacement and double replacement) as being balanced or not balanced.

  4. Evidence of Chemical Reactions Chemical reaction - process by which the atoms of one or more substances are rearranged to form different substances - temperature change, color change, odor change, gas given off, sudden appearance of solid

  5. Representing Chemical Reactions Reactants - starting substances Products - substances that are formed Chemical Equations “” read as yields or produces Reactants  Products

  6. Commonly used symbols in chemical equations + - used to separate one or more reactants or products (s) - solid (l) - liquid (g) - gas (aq) - aqueous - dissolved in water

  7. Conservation of Mass • Law of Conservation of Mass – mass is never created or destroyed in a chemical reaction • Mass of the reactants equals the mass of the products • Example: 50g of reactants MUST yield 50g of product!!

  8. Chemical Equations Equations must be balanced to keep from violating the Law of Conservation of Mass - use coefficients to balance - can only be put in front of formulas!!!

  9. Steps to Balance Equations 1.) Write equation for reaction (may already be done for you) 2.) Put the symbols of each element in a column under the reactants and products 3.) Count the number of each atom on both sides of the equation

  10. 4.) Change coefficientsONLY on either side of the equation to balance out the number of each atom 5.) Make sure coefficients are in lowest whole number ratios

  11. 2 Fe (s) + Cl2 (g)  FeCl3 (s) 3 2 2 1 1 2 Fe Cl 6 2 3 6

  12. Aqueous sodium hydroxide and aqueous calcium bromide react to produce solid calcium hydroxide and aqueous sodium bromide Ca+2Br-1 Ca+2OH-1 Na+Br-1 Na+OH-1 2 NaOH(aq) + CaBr2(aq)  Ca(OH)2(s) +NaBr(aq) 2 2 1 1 2 Na 2 1 OH 2 1 Ca 1 2 Br 1 2

  13. YOUR TURN!!

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