Balancing Equations and types of chemical reactions

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Balancing Equationsand types of chemical
reactions
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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

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How is this Accomplished?

• Chemical equations are balanced by adding
  coefficients in front of the substances in the
  equation.
• 1 MgF2 1 Li2CO3 ? 1 MgCO3 2 LiF
• Never change the subscript to balance equations

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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 Hs and Os.

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Some practice problems

• Here are some practice problems.
• 1. __NaCl __BeF2 --gt __NaF __BeCl2
• 2NaCl BeF2 ? 2NaF BeCl2
• 2. __FeCl3 __Be3(PO4)2 --gt __BeCl2 __FePO4
• 2FeCl3 Be3(PO4)2 --gt 3BeCl2 2FePO4

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• 3. __AgNO3 __LiOH --gt __AgOH __LiNO3
• AgNO3 LiOH --gt AgOH LiNO3
• 4. __CH4 __O2 --gt __CO2 __H2O
• CH4 2O2 --gt CO2 2H2O
• 5. __Mg __Mn2O3 --gt __MgO __Mn
• 3Mg Mn2O3 --gt 3MgO 2Mn

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

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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

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Synthesis A B ? AB

• Synthesis putting together
• H2(g) Cl2(g) ----gt 2HCl(g)
• C(s) O2(g) ----gt CO2(g)
• CaO(s) H2O(l) ----gt Ca(OH)2(s)

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Decomposition AB ? A B

• Decomposition breaking apart
• C12H22O11(s) ----gt12C(s) 11H2O(g)
• Pb(OH)2(s) ----gt PbO(s) H2O(g)
• 2Ag2O(s) ----gt 4Ag(s) O2(g)

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Single Replacement A BC ? B AC

• Single replacement reactions - When one element
  displaces another element in a compound
• Zn(s) H2SO4(aq) ----gt ZnSO4(aq) H2(g)
• 2Al(s) 3CuCl2(aq) ---gt 2AlCl3(aq) 3Cu(s)
• Cl2(g) KBr(aq) ----gt KCl(aq) Br2(l)

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Single Replacement Reactions follow the Activity
Series
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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 ?

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Double Replacement AB CD ? AD CB

• Double Replacement reaction chemical reaction
  where two reactant ionic compounds exchange ions
  to form two new product compounds with the same
  ions.
• AgNO3(aq) NaCl(aq) ----gt AgCl(s) NaNO3(aq)
• ZnBr2(aq) 2AgNO3(aq) ----gt Zn(NO3)2(aq)
  2AgBr(s)
• H2SO4(aq) 2NaOH(aq) ----gt Na2SO4(aq) 2H2O(l)

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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.

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Example

• HCl NaOH ? NaCl HOH
• H2SO4 Mg(OH)2 ? MgSO4 H2O
• H3PO4 Al(OH)3 ?

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Combustion Burning (add O2)

• CH4(g) 2O2(g) ----gt 2H2O(g) CO2(g)
• C2H6(g) O2(g) ----gt H20(g) CO2(g)
• C3H8(g) O2(g) ----gt H2O(g) CO2(g)
• H2(g) O2(g) ----gt H2O(g)
• Mg(g) O2(g) ----gt MgO(s)

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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

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• 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.

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Examples

• Fe2 ? Fe3 e-
• Cl2 2e- ? 2Cl-
• Fe3 e- ? Fe2
• Cu2 2e- ? Cu
• Zn ? Zn2 2e-