Download Unit 5: The Mole and Stoichiometry

Unit 5: The Mole and
Stoichiometry
What Can A Coefficient Equal?
• A coefficient represents the number of
elements or molecules in a chemical equation. It
is different from a subscript which measures
the number of atoms or polyatomic ions within a
molecule.
•
2 CO + O 2  2 CO 2
C oefficients
• Come
in front of an element
or molecule
• Big numbers
• Means that every element
or molecule in a compound
get multiplied by it.
S ubscripts
• Come
after an element
or polyatomic ion
• Small numbers
• Only tell how many of
an element there are
within a compound
A Coefficient can represent two
different things:
1. Number of molecules of a reactant or
product in an equation.
2. Number of moles of a reactant or
product in an equation.
• In either case, the coefficients give the ratio
between the numbers in a chemical reaction
(this is why balancing is important)!
• 2CO(g) + 1O2(g)  2CO2
• The reactant ratio is 2:1
Using the Mole
• Coefficients in balanced chemical
equations represent MOLES or Molecules
• Zn + 2 HCl  ZnCl2 + H2
1 mole (or atom) of Zn reacts with 2 moles
(or molecules) of hydrochloric acid to
produce 1 mole(or molecule) of zinc
chloride and 1 mole(or molecule) of
hydrogen gas.
Back to the reaction
• Zn + 2 HCl  ZnCl2 + H2
• To carry out this reaction, how much zinc
and HCl will be needed to make the
reaction go to completion?
• 1 mole of Zn and 2 moles of HCl
• How many moles of HCl will be needed if I
have 2 moles of zinc?
4 moles of HCl
• How many moles of Copper (I) Sulfide
could be produced from 6 moles of Copper
(I) Chloride reacting with an excess of H2S
gas?
1. Write a balanced equation. Determine what
you start with and what you want to know.
H2S + 2 CuCl  Cu2S + 2 HCl
H2S +
2CuCl  Cu2S +
2HCl
2. Covert moles of what you start with to moles of
•
•
what you want to know using a mole ratio.
*A mole ratio compares two products or
reactants using the coefficients of the balanced
equation
(in this case 2 moles CuCl:1 mole Cu2S).
6 moles CuCl
1 mole Cu2S
2 moles CuCl
= 3 moles Cu2S
H2S +
2CuCl  Cu2S +
2HCl
• How many moles of HCl would be
produced starting with the same amount?
6 moles CuCl
2 moles HCl
2 moles CuCl
= 6 moles HCl
2 Al +
3 H2CO3 
Al2(CO3) 3 + 3 H2
• Suppose Carlos gets 10 moles of
Aluminum for his birthday. How much of
each product can he make?
10 moles Al
1 mole Al2(CO3)3
2 moles Al
10 moles Al
3 moles H2
2 moles Al
= 5 moles
Al2(CO3)3
= 15 moles H2