Chemical Equations

1
Chemical Equations
2
Conservation of Mass

• Law of Conservation of Mass mass is never
  created or destroyed in a chemical reaction
• Mass of the reactants equals the mass of the
  products

3
Chemical Equations
Equations must be balanced to keep from violating
the Law of Conservation of Mass
- use coefficients to balance - can only be
put in front of formulas
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Steps to Balance Equations
1.) Write equation for reaction (may
already be done for you) 2.) Put the symbols of
each element in a column
under the yields sign (Polyatomic ions may be
grouped together if they remain intact on both
sides of the equation)
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3.) Count the number of each atom (or
polyatomic ions) on both sides of the
equation 4.) Change coefficients on either side
of the equation to balance out the number of each
atom 5.) Make sure coefficients are in lowest
whole number ratios
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Fe (s) Cl2 (g) ? FeCl3 (s)
3
2
2
1
1
2
2
Fe Cl
2
3
6
6
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Aqueous sodium hydroxide and aqueous calcium
bromide react to produce solid calcium hydroxide
and aqueous sodium bromide
NaOH-1
Ca2Br-1
NaBr-1
Ca2OH-1
NaOH(aq) CaBr2(aq) ? Ca(OH)2(s)
NaBr(aq)
2
2
1
1
2
2
Na
2
OH
1
2
Ca
1
1
Br
2
1
2