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Balancing Equations

Balancing Equations. The Abbreviated Version. What is a Chemical Equation?. An equation is a short-hand way of writing a chemical reaction. Reactants are on the left, products are on the right. Mg + 2HCl  MgCl 2 + H 2 reactants products. How is this Accomplished?.

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Balancing Equations

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  1. Balancing Equations The Abbreviated Version

  2. What is a Chemical Equation? • An equation is a short-hand way of writing a chemical reaction. • Reactants are on the left, products are on the right. • Mg + 2HCl  MgCl2 + H2 • reactants products

  3. How is this Accomplished? • This is accomplished by adding coefficients in front of the substances in the equation.

  4. Tips for Balancing Equations • 1. Balance metals first. • 2. Balance nonmetals except H and O. • 3. If polyatomic ions are conserved in the reaction, then try balancing them as a unit. • 4. Balance any remaining H’s and O’s.

  5. Some practice problems: • Here are some practice problems. • 1. __NaCl + __BeF2 --> __NaF + __BeCl2 • 2. __FeCl3 + __Be3(PO4)2 --> __BeCl2 + __FePO4

  6. 3. __AgNO3 + __LiOH --> __AgOH + __LiNO3 • 4. __CH4 + __O2 --> __CO2 + __H2O • 5. __Mg + __Mn2O3 --> __MgO + __Mn

  7. 7. Na + H2O  NaOH + H2 • 8. H2SO4 + Ca(OH)2 CaSO4 + H2O

  8. Types of Chemical Reactions • There are 5 overall types of chemical reactions: • 1. Synthesis or Combination • 2. Decomposition • 3. Single Replacement • 4. Double Replacement • 5. Combustion

  9. Synthesis: A + B  AB • Examples: • H2(g) + Cl2(g) ----> 2HCl(g) • C(s) + O2(g) ----> CO2(g) • CaO(s) + H2O(l) ----> Ca(OH)2(s)

  10. Decomposition: AB  A + B • C12H22O11(s) ---->12C(s) + 11H2O(g) • Pb(OH)2(s) ----> PbO(s) + H2O(g) • 2Ag2O(s) ----> 4Ag(s) + O2(g)

  11. Single Replacement: A+ BC  B + AC • Zn(s) + H2SO4(aq) ----> ZnSO4(aq) + H2(g) • 2Al(s) + 3CuCl2(aq) ---> 2AlCl3(aq) + 3Cu(s) • Cl2(g) + KBr(aq) ----> KCl(aq) + Br2(l)

  12. Single Replacement Reactions follow the Activity Series

  13. The element by itself has to be more reactive than the one it is trying to replace. Examples: • Mg + Zn(NO3)2 • Mg + AgNO3  • Mg + LiNO3  • Zn + H2SO4  • Na + H2O  • Sn + NaNO3  • Cl2 + NaBr 

  14. Double Replacement: AB + CD  AD + CB • AgNO3(aq) + NaCl(aq) ----> AgCl(s) + NaNO3(aq) • ZnBr2(aq) + 2AgNO3(aq) ----> Zn(NO3)2(aq) + 2AgBr(s) • H2SO4(aq) + 2NaOH(aq) ----> Na2SO4(aq) + 2H2O(l)

  15. Special Type of Double Replacement: Neutralization • A neutralization reaction occurs between an acid and a base. • A base is a metallic hydroxide, such as NaOH, KOH, Ca(OH)2, Al(OH)3, etc. • An acid and a base always react to form a salt and water.

  16. Example: • HCl + NaOH  NaCl + HOH • H2SO4 + Mg(OH)2  MgSO4 + H2O • H3PO4 + Al(OH)3 

  17. Combustion: Burning (add O2) • CH4(g) + 2O2(g) ----> 2H2O(g) + CO2(g) • C2H6(g) + O2(g) ----> H20(g) + CO2(g) • C3H8(g) + O2(g) ----> H2O(g) + CO2(g) • H2(g) + O2(g) ----> H2O(g) • Mg(g) + O2(g) ----> MgO(s)

  18. Another type of reaction: oxidation-reduction or redox • In these, the charges on some of the atoms involve change because of an electron transfer. • Oxidation Is Loss of electrons. • Reduction Is Gain of electrons. • Remember “OIL RIG”

  19. When oxidation occurs, the charge on the atom or ion is increased. • When reduction occurs, the charge on the atom or ion is decreased. • One thing to remember: The charge on an element by itself is 0.

  20. Examples: • Fe+2 Fe+3 + e- • Cl2 + 2e-  2Cl- • Fe+3 + e-  Fe+2 • Cu+2 + 2e-  Cu • Zn  Zn+2 + 2e-

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