WRITING CHEMICAL EQUATIONS

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WRITING CHEMICAL EQUATIONS

• Reactants (starting materials) ? Products (ending
  materials)
• (g) gas (l) liquid (s) solid
• (aq) aqueous D heat ? yields
• (dissolved in water)
• X
• ? catalyst combines
• The number of molecules (moles) involved in
  the reaction are written in the front of the
  chemical formula.

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WRITING CHEMICAL EQUATIONS

• Reactants (starting materials) ? Products (ending
  materials)
• 2 Na(s) Cl2(g) ? 2 NaCl(s)
• should be read as
• 2 moles (or molecules) of sodium metal in its
  solid state combined with one mole (or molecule)
  of chlorine gas to produce two moles (or
  molecules) of sodium chloride in the solid state.

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CHEMICAL EQUATIONS

• CHEMICAL EQUATIONS represent chemical reactions
  which, in turn, are driven by changes like
• Change Observation
• formation of a precipitate solid is formed
• formation of water heat is formed
• formation of a gas bubbles formed
• other changes are
• Electrochemistry electrons are transferred
• Thermochemistry heat is transferred

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CHEMICAL EQUATIONS

• There are three basic types of chemical
  equations
• Molecular, Ionic, Net ionic.
• MOLECULAR EQUATIONS are written as if all
  substances were molecular, even though some
  substances may exist as ions.
• HCl (aq) NaOH (aq) ? NaCl (aq) H2O (l)

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CHEMICAL EQUATIONS

• IONIC EQUATIONS have the substances which exist
  as ions written in ionic form.
• H (aq) Cl- (aq) Na (aq) OH-(aq) ? Na
  (aq) Cl- (aq) H2O (l)
• Precipitation, Acid/base, and Redox reactions can
  all be written depicting the appropriate
  substances as ions.

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CHEMICAL EQUATIONS

• NET IONIC EQUATIONS are ionic equations with the
  Spectator ions removed.
• H (aq) OH-(aq) ? H2O (l)
• SPECTATOR IONS do not participate in a reaction
  (that is they do not react to form a new
  substance). Common Spectator ions are Group I,
  many Group II, and NO3- (nitrate) and C2H3O2-
  (acetate) ions.

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PRACTICE PROBLEMSCHEMICAL EQUATIONS

• Write the ionic and net ionic equation for the
  following unbalanced molecular equations.
• 1. Na2SO4(aq) BaCl2(aq) ? BaSO4(s) NaCl(aq)
• 2. Al(s) H2SO4(aq) ? Al2(SO4)3(aq) H2(g)
• 3. NO2(g) H2O(l) O2(g) ? HNO3(aq)
• 4. HCl(aq) Fe2(SO4)3(aq) ? FeCl3(aq)
  H2SO4(aq)
• Remember, (aq) stands for ions dissolved in water

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CHEMICAL EQUATIONSanswers

• 1. Na2SO4(aq) BaCl2(aq) ? BaSO4(s) NaCl(aq)
• Ionic
• Na SO42- Ba2 Cl- ? BaSO4(s) Na Cl-
• Net ionic
• SO42-(aq) Ba2(aq) ? BaSO4(s)
• Al(s) H2SO4(aq) ? Al2(SO4)3(aq) H2(g)
• Ionic
• Al(s) H SO42- ? Al3 SO42- H2(g)
• Net ionic
• Al(s) H(aq) ? Al3(aq) H2(g)

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CHEMICAL EQUATIONSanswers

• 3. NO2(g) H2O(l) O2(g) ? HNO3(aq)
• NO2(g) H2O(l) O2(g) ? H(aq) NO3-(aq)
• the ionic and net ionic equations are the same!
• 4. HCl(aq) Fe2(SO4)3(aq) ? FeCl3(aq)
  H2SO4(aq)
• H Cl- Fe3 SO42- ? Fe3 Cl- H SO42-
• N.R.
• No reaction occurs! All species are spectator
  ions.

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CHEMICAL EQUATIONS

• In a chemical reaction, atoms can be neither
  created nor destroyed therefore the total number
  of atoms on the reactant side must equal the
  total number of atoms on the product side of the
  equation.
• This is known as BALANCING AN EQUATION.
• Once the reactants products have been
  identified, remember the relative ratio of one
  atom to another in a formula can not be altered.
  
• H2O is the formula for water and it is safe to
  drink but if it is changed to H2O2 (hydrogen
  peroxide) it is no longer safe for drinking. It
  is a completely different substance!
• Equations must be balanced by changing the
  number in front of the formula and not by
  changing the chemical formula.

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BALANCING CHEMICAL EQUATIONS Mg O2 ? MgO

• First list all atoms in order of metals,
  nonmetals, then H O last. Leave the
  species that is split between more than one
  compound for last.
• Mg - 1 Mg - 1
• O - 2 O - 1
• Next, start with the top atom one Mg on the
  reactant side and one Mg atom on the product
  side. The Mg atom is balanced. Now do oxygen,
  two O atoms on the reactant side and one on the
  product side. The product side needs to change
  so place a 2 in front of MgO. Remember you can
  not change the formula.
• Mg O2 ? 2 MgO
• This now makes the list
• Mg - 1 Mg - 2
• O - 2 O - 2
• If a two is placed in front of the Mg on the
  reactant side
• 2 Mg O2 ? 2 MgO
• Mg - 2 Mg - 2
• O - 2 O - 2
• Now the equation is balanced.

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PRACTICE PROBLEMSBALANCING CHEMICAL EQUATIONS

• Balance the following chemical equations. The
  answers are found on the next slide.
• 1. __Na2SO4(aq) __BaCl2(aq) ? __BaSO4(s)
  __NaCl(aq)
• 2. __Al(s) __H2SO4(aq) ? __Al2(SO4)3(aq)
  __H2(g)
• 3. __NO2(g) __H2O(l) __O2(g) ? __HNO3(aq)
• 4. __Al(s) __HCl(aq)? __AlCl3(aq) __H2(g)
• 5. __C3H8(g) __O2(g) ? __CO2(g) __H2O(g)

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BALANCING CHEMICAL EQUATIONS

• Answers
• 1. __Na2SO4(aq) __BaCl2(aq) ? __BaSO4(s)
  _2_NaCl(aq)
• 2. _2_Al(s) _3_H2SO4(aq) ? __Al2(SO4)3(aq)
  _3_H2(g)
• 3. _4_NO2(g) _2_H2O(l) __O2(g) ? _4_HNO3(aq)
• 4. _2_Al(s) _6_HCl(aq)? _2_AlCl3(aq)
  _3_H2(g)
• 5. __C3H8(g) _5_O2(g) ? _3_CO2(g) _4_H2O(g)

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PRACTICE PROBLEMS 16

• Balance the following molecular equations then
  write both the ionic net ionic equations
• 1. __Na2CO3(aq) __HNO3(aq) ? __H2CO3(aq)
  __NaNO3 (aq)
• Note carbonic acid decomposes into carbon
  dioxide and water.
• 2. __KBr(aq) __I2(g) ? __ KI(aq) __Br2(l)
• 3. __AlCl3(aq) __K3PO4(aq) ? __AlPO4(s)
  __KCl(aq)

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Answers to PRACTICE PROBLEMS 16

• 1. Na2CO3(aq) 2 HNO3(aq) ? H2CO3(aq) 2
  NaNO3 (aq)
• Note carbonic acid decomposes into carbon
  dioxide and water.
• Ionic Na CO32- H NO3- ? H2O (l) CO2(g)
  Na NO3-
• Net ionic CO32- H ? H2O (l) CO2(g)
• 2. 2KBr(aq) I2(g) ? 2 KI(aq) Br2(l)
• Ionic K Br- I2(g) ? K I- Br2(l)
• Net ionic 2Br- I2(g) ? 2I- Br2(l)
• 3. AlCl3(aq) __K3PO4(aq) ? __AlPO4(s) 3
  KCl(aq)
• Ionic Al3 Cl- K PO43- ? AlPO4(s) K
  Cl-
• Net ionic Al3 PO43- ? AlPO4(s)

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GROUP STUDY PROBLEM 16

• Balance the following molecular equations then
  write both the ionic net ionic equations
• 1. __Na2SO4(aq) __AlCl3(aq) ? __Al2(SO4)3(aq)
  __NaCl(aq)
• 2. __NaBr(aq) __Cl2(g) ? __ NaCl(aq)
  __Br2(l)
• 3. __SbCl3(aq) __Na2S(aq) ? __Sb2S3(s)
  __NaCl(aq)
• 4. __Mg(OH)2(aq) __ H2SO4(aq)? __ H2O(l)
  __MgSO4(aq)
• 5. __C2H4(g) __O2(g) ? __CO2(g) __H2O(g)