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Chemical Reactions

Chemical Reactions. Introduction. Chemical Equations. chemical change = chemical reaction A chemical equation is a shorthand way of showing what happens when a chemical reaction occurs. Na + Cl  NaCl Symbols and formulas in the equation represent reactants and products.

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Chemical Reactions

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  1. Chemical Reactions Introduction

  2. Chemical Equations • chemical change = chemical reaction • A chemical equation is a shorthand way of showing what happens when a chemical reaction occurs. Na + Cl  NaCl • Symbols and formulas in the equation represent reactants and products.

  3. Reactants and Products • Reactants are the “starting substances”. They are written on the left side of the equation. • Products are the new substances formed as a result of the chemical change. They are written on the right side of the equation. Na + Cl  NaCl Reactants Products

  4. Wrap-Up 1 • Label the reactants and products in the equation below: • 2 H2 + O2 2 H2O Reactants Products

  5. Reactants  Products“Yield” An arrow pointing to the right () is written between the reactants and the products. Na + Cl  NaCl The arrow indicates when reactants on the left chemically react…. ….they “yield” the products on the right.

  6. Two Kinds of Numbers in Equations • Subscript - written to lower right of symbol. Multiplies only symbol it comes after. • H2O – two H atoms, one O atom • Coefficient - written before symbol or formula. Multiplies whole formula. • 2 NaCl – two Na atoms, two Cl atoms

  7. chemical equations must balance The number of atoms of each element is the same after a reaction as before the reaction

  8. Balanced Equations • In a balanced equation, • # of atoms of each element on the left equals • # of atoms of that element on the right

  9. 2Na + 2H2O  2NaOH + H2 • There are 2 Na atoms on the left and 2 Na atoms on the right. • There are 4 H atoms on the left and 4 H atoms on the right • There are 2 O atoms on the left and 2 O atoms on the right. • Is the equation balanced?

  10. Wrap-Up 2 • Are these equations balanced? YES NO

  11. SYNTHESIS A +B AB

  12. DECOMPOSITION AB A +B

  13. SINGLE REPLACEMENT A +BC AC+B

  14. DOUBLE REPLACEMENT AB+XYAY+XB

  15. COMBUSTION CxHy+O2 CO2+H2O+heat

  16. 2H2 + O22H2O AgNO3 +NaCl AgCl + NaNO3 Zn + H2SO4ZnSO4 + H2 2H2O 2H2 + O2 CH4 + 2O2 CO2 + 2H2O 2CO + O2 2CO2 2HgO 2Hg + O2 2KBr + Cl22KCl + Br2 CaO + H2O Ca(OH)2 2H2O22H2O + O2 Ca(OH)2 + H2SO4CaSO4 + 2H2O

  17. Exothermic Reaction Reactants Products Energy Temperature Energy released Time Time Gets Hotter Energy released by reactants

  18. Endothermic Reaction Reactants Products Energy Temperature Time Time Gets Cooler Energy absorbed by reactants

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