Chemical Equations and Chemical Reactions

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Chemical Equations and Chemical Reactions
http//www.personal.kent.edu/cearley/ChemWrld/bal
ance/balance.htm
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Writing A Chemical Equation

• The general format for chemical equations is
• a b ? c d
• The substances on the left side of the equation
  (a and b in this case) are called the reactant(s).

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• The sign means reacts with.
• The ? means produces or yields.
• The substance(s) on the right side of the
  equation (c and d in this case) are called the
  product(s).

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• Lets work with the statement Hydrogen gas reacts
  with oxygen gas to form liquid water.

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• Word Equation
• hydrogen oxygen ? water
• Skeleton Equation
• H2(g) O2(g) ? H2O(l)
• Balanced Equation
• ___H2(g) ___O2(g) ? ___H2O(l)
• 2H2(g) O2(g) ? 2H2O(l)

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Why must we balance equations?

• The Law of Conservation of Mass states that the
  total mass of reactants is always equal to the
  total mass of the products. (Lavoisiers law)

Antoine-Laurent Lavoisier experimenting to
determine the composition of water, French
engraving, 19th century. http//www.britannica.co
m/eb/art-15464/Antoine-Laurent-Lavoisier-experimen
ting-to-determine-the-composition-of-water
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Why must we balance equations?

• Daltons atomic theory states that atoms can not
  be created or destroyed. Compounds are formed
  when atoms of different elements combine in fixed
  proportions.

John Dalton, F.R.S., engraved by Worthington
after an 1814 painting by William Allen,
published 25 June 1823 in Manchester and London.
Note the charts with Dalton's atomic symbols
lying on the table. Fisher Collection, Chemical
Heritage Foundation.
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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 (small numbers). You do not write
  coefficients of 1 (one).
• 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)
• Rules For Writing Balanced Chemical Equations
• This requires a lot of practice and patience.
  These rules will not apply in all equations.
• 1. Write the skeleton equation.

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1. Look for a polyatomic ion that appears once on
   each side of the equation. Balance these first.
2. Pick single elements that appears on each side.
   Choose coefficients to balance this element.
   The terms you balanced in the previous step have
   to remain balanced. Repeat for any other
   elements.

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• 4. Check for any term you have not yet looked at.
  Adjust the coefficient of the term so that the
  numbers of the elements appearing in that term
  are balanced across the whole equation. If you
  have any fraction coefficients clear them by
  multiplying. Also, make sure you have the
  smallest possible coefficients by reducing.
• 5. Check the equation!

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Example 1

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

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Example 2

• Balanced Chemical Equation
• 2H2O__ 2Na__ ? 2NaOH__ H2___
• 2H2O(l) 2 Na(s) ? 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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Example 2

• 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__ NaNO3__
• Ca(NO3)2(aq) 2NaOH(aq) ? Ca(OH)2(s) NaNO3(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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Homework?p. 174 1 to 6
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