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Chapter 8

Chapter 8. Chemical Reactions. Reactants Products. + - separates reactants and products - “yields” - reversible reaction (s) - solid (l) - liquid (g) - gas. (aq) – aqueous solution, dissolves in H 2 O - heat Pt - catalyst.

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Chapter 8

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  1. Chapter 8 Chemical Reactions

  2. Reactants Products • + - separates reactants and products • - “yields” • - reversible reaction • (s) - solid • (l) - liquid • (g) - gas

  3. (aq) – aqueous solution, dissolves in H2O • - heat • Pt - catalyst

  4. Examples • Fe (s) + O2 (g) Fe2O3 (s) 4Fe (s) + 3O2 (g) 2Fe2O3 (s)

  5. Balancing Chemical Equations • Balanced equations obey the law of conservation of matter. • Balanced Equation – must have the same number of atoms of each element in both sides of the equation.

  6. Examples • C(s) + O2(g) CO2(g) 1 C + 2O 1C + 2O

  7. More Examples • 2C(s) + O2(g) 2CO 2C 2O 2C 2O

  8. Rules for Balancing Equations • 1) Determine the correct formulas for reactants and products • 2) Write the reaction • 3) Count the number of atoms of each element in the reactants and products (a poly-atomic ion appearing unchanged on both sides of the equation is counted as a single unit)

  9. Rules Cont’d • 4) Balance elements 1 at a time using coefficients • Coefficient: small whole # that appears in front of a formula in an equation • Balance O & H last • You cannot change subscripts

  10. Rules Cont’d • 5) Check to see if each atom is balanced • 6) Make sure Coefficients are lowest possible numbers

  11. Example • H2 + O2 H2O 2 1 2 4H2 + 2O2 4H2O

  12. Combination Reactions • Two or more substances react to form a single substance

  13. Formation of Binary Salts • M + X MX • Example • 2Na + Cl2 2NaCl

  14. Formation of Binary Oxides • M + O2 MO • Example • 2Zn + O 2 2ZnO

  15. Formation of Binary Acids • Examples • H2 + X HX • H2 + Cl2 2HCl

  16. Formation of Ternary Acids • Examples • H2O + nonmetallic oxide oxyacid • P2O5 + 3H2O 2H3PO4

  17. Formation of Bases • Examples • MO + H2O MOH • CaO + H2O Ca(OH)2

  18. Formation of Ternary Salts • Examples • MO + XOn MXOn+1 • CaO + CO2 CaCO3

  19. Decomposition Reactions • A single compound is broken down into 2 or more simpler products. • A B + C • CaCO3 CaO + CO2 • They can be a combination of elements and compounds

  20. Binary Compounds break down into constituent elements • Decomposition reactions require energy - (heat, light or electricity) • Example • 2H2O(l)electricity 2H2(g) + O2(g)

  21. Single Replacement Reactions • Atoms of an element replace the atoms of a second element in a compound • Gen Rxn: A + BC AC + B • Example • Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)

  22. How do you know this will happen? • Whether one metal will replace another is determined by the relative activity of the 2 metals.

  23. Activity Series • Lists metals in order of decreasing reactivity • A positive metal will replace any metal found below it in the activity series • Metals from Li to Na replace H from acids and H20; Mg to Pb replace H from acids only.

  24. Double Replacement Rxns • Involve an exchange of positive ions between two compounds. • Generally take place in aqueous solutions

  25. For a double displacement rxn to occur one of the following must be true: • A precipitate forms • A gas forms and bubbles out of mixture • A molecular compound forms (ie H2O)

  26. Examples • AB + CD AD + CB AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

  27. Combustion Rxns • Oxygen reacts with another substance, producing energy in the form of heat or light. • Example • CxHy + O 2 CO2 + H2O

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