Chemical Equations and Chemical Reactions

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Chemical Equationsand Chemical Reactions
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Writing A Chemical Equation

• The general format for chemical equations is
• a b ? c d

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What Does It All Mean?

• a b ? c d
• The reactants go on the left side of the equation
  (a and b in this case).
• The sign means reacts with.
• The ? means produces or yields.
• The products go on the right side of the equation
  (c and d in this case).

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• Lets work with the statement
• Hydrogen gas reacts with oxygen gas to form
  liquid water
• Word Equation
• hydrogen oxygen ? water
• Skeleton Equation
• H2 O2 ? H2O

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• To balance equations numbers called
  coefficients are put before the formulas. This
  changes the number of molecules. You cannot add
  or change subscripts. You do not write
  coefficients of 1 (one).
• Balanced Equation
• ___H2 ___O2 ? ___H2O
• 2H2 O2 ? 2H2O

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• Why Must We Balance Equations?
• Remember the Law of Conservation of Mass states
  that the total mass of reactants is always equal
  to the total mass of the products.
• Daltons Atomic Theory states that atoms can not
  be created or destroyed. Compounds are formed
  when atoms of different elements combine in fixed
  proportions.

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• Sometimes you need to know the state of the
  chemicals that are involved in a chemical
  reaction.

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State Abbreviation
solid
liquid
gas
aqueous solution
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State Abbreviation
solid (s)
liquid
gas
aqueous solution
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State Abbreviation
solid (s)
liquid (l)
gas
aqueous solution
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State Abbreviation
solid (s)
liquid (l)
gas (g)
aqueous solution
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State Abbreviation
solid (s)
liquid (l)
gas (g)
aqueous solution (aq)
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• Final Balanced Chemical Equation
• 2H2(g) O2(g) ? 2H2O(l)

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Step 1

• Write in the symbols for all atoms and ions
  (skeleton equation)
• Balance each compound
• Remember diatomic ions H2, N2, O2, F2, Cl2,
  Br2, I2
• Remember to look for polyatomic ions on both
  sides of the equation
• iron water ? hydrogen gas iron (III)
  oxide
• Fe H2O ? H2 Fe2O3

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Step 2

• Write in the abbreviations for the state of each
  compound if known or given
• Solid (s) ex. Fe (s)
• Liquid (l) ex. H2O (l)
• Gas (g) ex. He (g)
• Aqueous solution (aq) ex. NaCl (aq)
• Fe (s) H2O (l) ? H2 (g) Fe2O3 (s)

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Step 3 Balance Equation

• Balance the equation by adding coefficients
• Pick single elements that appear on each side
  first to balance
• Remember leave O then H until the end
• Go back and re-check that all atoms are equal on
  both sides
• If you have any fraction coefficients clear them
  by multiplying.
• Also, make sure you have the smallest possible
  coefficients by reducing the ENTIRE EQUATION.
• 2Fe (s) 3H2O (l) ? 3H2 (g) Fe2O3 (s)

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• Example 1
• Word Equation
• sodium water ?
• sodium hydroxide hydrogen gas
• Skeletal Equation
• Na H2O ? NaOH H2
• Balanced Equation
• ___Na ___H2O ? ___NaOH ___H2
• 2Na 2H2O ? 2NaOH H2

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• Balanced Chemical Equation
• 2H2O__ 2Na__ ? 2NaOH__ H2___
• 2Na(s) 2H2O (l) ? 2NaOH(aq) H2(g)Verification

Reactants Products
2 Na atoms 2 Na atoms
4 H atoms 4 H atoms
2 O atoms 2 O atoms
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• Example 2
• Word Equation
• copper silver nitrate ? copper(II) nitrate
  silver
• Skeletal Equation
• ___ ______ ? ______ ___
• Cu AgNO3 ? Cu(NO3)2 Ag

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• Balanced Equation
• __Cu __ AgNO3 ? __Cu(NO3)2 __Ag
• Cu 2AgNO3 ? Cu(NO3)2 2Ag
• Balanced Chemical Equation
• Cu__ 2AgNO3__ ? Cu(NO3)2__ 2Ag__
• Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq) 2Ag(s)

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Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq)
2Ag(s) Verification
Reactants Products



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Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq)
2Ag(s) Verification
Reactants Products
1 Cu atom


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Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq)
2Ag(s) Verification
Reactants Products
1 Cu atom 1 Cu atom


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Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq)
2Ag(s) Verification
Reactants Products
1 Cu atom 1 Cu atom
2 Ag atoms

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Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq)
2Ag(s) Verification
Reactants Products
1 Cu atom 1 Cu atom
2 Ag atoms 2 Ag atoms

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Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq)
2Ag(s) Verification
Reactants Products
1 Cu atom 1 Cu atom
2 Ag atoms 2 Ag atoms
2 NO3- ions
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Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq)
2Ag(s) Verification
Reactants Products
1 Cu atom 1 Cu atom
2 Ag atoms 2 Ag atoms
2 NO3- ions 2 NO3- ions
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• Example 3
• Word Equation
• calcium nitrate sodium hydroxide ? calcium
  hydroxide sodium nitrate
• Skeletal Equation
• Ca(NO3)2 NaOH ? Ca(OH)2 NaNO3
• Balanced Equation
• __Ca(NO3)2 __NaOH ? __Ca(OH)2 __NaNO3
• Ca(NO3)2 2NaOH ? Ca(OH)2 2NaNO3

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• Balanced Chemical Equation
• Ca(NO3)2__ 2NaOH__ ? Ca(OH)2__ 2NaNO3____
• Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)

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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products




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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom



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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom



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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom
2 NO3- ions


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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom
2 NO3- ions 2 NO3- ions


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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom
2 NO3- ions 2 NO3- ions
2 Na atoms

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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom
2 NO3- ions 2 NO3- ions
2 Na atoms 2 Na atoms

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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom
2 NO3- ions 2 NO3- ions
2 Na atoms 2 Na atoms
2 OH- ions
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Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom
2 NO3- ions 2 NO3- ions
2 Na atoms 2 Na atoms
2 OH- ions 2 OH- ions
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