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Coefficients and Subscripts (Page 62)
Chemical Equations have two kinds of numbers: Subscripts and Coefficients
A subscript, like the 2 in H2O, tells how many of an atom there are in any one molecule of a
compound, so H2O has 2 Hydrogens and 1 Oxygen atom per water molecule.
A coefficient, on the other hand, tells you how many molecules of a compound you need to
perform a chemical reaction. So if a chemical reaction says 2HCl + 2Na -> 2NaCl + H2, that
means that there are 2 Hydrochloric Acid molecules in the reactants, with 1 Hydrogen
atom and 1 Chlorine atom each
3 H2O
The coefficient tells how many units
of the compound take part in the
reaction
The subscript tells how many atoms
are in each molecule of the
compound
In order to figure out how many total atoms are in an equation, you need to multiply the
coefficient by the Subscript. In the above example, 2HCl has 2 H Atoms (2*1) and 2 Cl Atoms
(2*1 again). If part of a chemical equation read 3H2O, those 3 water molecules, would have a
total of 6 Hydrogen atoms (2*3) and 3 (Oxygen atoms)
The Steps:
1) List the elements' symbols vertically.
2) For each element, multiply the coefficient by the subscript to get the total number
of atoms.
a. Remember that any unwritten number is 1.
Try and figure out the total atoms for the following chemical formulae (not full equations) with
coefficients
1. 2 H2O
2. 3 HNO3
3. 5 C3H8
4. 6 C6H12O6
5. 8 PbNO3