Law of Conservation of Mass – The amount of matter that exists in the universe cannot change. This means that the
atoms that exist today are the same ones (or parts of the same ones) that existed billions of years ago. You have some
carbon atoms in you that spent time in Einstein’s body. Think about it, you are part Einstein. What this means to
chemical reactions is that there must always, always, always be the same number of product atoms as there are reactant
atoms.
Terms to Know:
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Reactants: ______________________________________________________________________
Products: ______________________________________________________________________
Yields Arrow: ____________________________________________________________________
Coefficient: _____________________________________________________________________
Subscript: ______________________________________________________________________
Practice: for each of the compounds, write the # of atoms for each element. Example: CO 2 – C=1, O=2
LiOH - ____________________________
3Ba(OH)2 - __________________________
2NaNO3 - __________________________
Al2(SO4)3 - ___________________________
CH3OH - ___________________________
4As2O5 -
___________________________
Balancing Equations:
Remember:
 A balanced equation MUST have the SAME number of EACH type of atom on BOTH sides of the yields arrow.
 An equation is balanced by changing the coefficients.
2 Things you CANNOT do when balancing an equation:
1) You cannot change a subscript.
2) You cannot place a coefficient in the middle of a chemical formula.
Balance the following equations:
Does the equation as written
obey the Law of
Conservation of Mass (Y/N)
Is the underlined
compound a Covalent or
Ionic Bond?
1) ___NaBr + _2__H3PO4  ___Na3PO4 + ___HBr
___________________
_______________
2) __C2H4 + _3_O2  _2_CO2 + _2_H2O
___________________
_______________
3) _4_PbSO4  _4_PbSO3 + _2_O2
___________________
_______________
Does the equation as written
obey the Law of
Conservation of Mass (Y/N)
Is the underlined
compound a Covalent or
Ionic Bond?
4) _2_NH3 + _3_I2  ___N2I6 + _3_H2
___________________
_______________
5) _3_H2O + _3_SO3  _3_H2SO4
___________________
_______________
_____________
_______________
7) _2__Mg + ___Fe2O3  ___Fe + ___MgO
___________________
_______________
8) ___SF4 + _2__H2O  ___SO2 + _4__HF
___________________
_______________
9) ___NaClO3  _3__NaCl + ___O2
___________________
_______________
6) ____Ca(OH)2 + ___Al2(SO4)3  ___CaSO4 + ___Al(OH)3