Predicting Products/Balancing Equations
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Practice
Problem #3
Practice
Problem #4
Here are the key steps (in order) to doing stoichiometry:
1. Identify the type of reaction [combustion,
synthesis, decomposition, single-replacement, or double replacement].
2. Write the products of the reaction based on
reaction type.
· double-replacement: cations take the place of cations, and anions
take the place of anions; then write
the chemical formulas canceling out the charges
3. Then, balance the equation.
Sample Example Problem [to show you how it's done]:
Problem: AlCl3 (aq) + Pb(NO3)2
(aq) --> ?
1. Identify the type of reaction.
Double-replacement reaction.
You
have 2 compounds made up of cations and anions.
AlCl3
(aq) + Pb(NO3)2
(aq) -->
2. Write out the products of the
chemical reaction.
Switch the cations,
since this is double-replacement:
AlCl3
+ Pb(NO3)2
--> Pb Cl + Al NO3
Then write the formulas of the products based on their
charges.
Pb = +2, Cl = -1, so the formula is PbCl2.
Al = +3, NO3 = -1, so the formula is Al(NO3)3.
AlCl3
+ Pb(NO3)2
--> PbCl2
+ Al(NO3)3
3. Balance the equation.
AlCl3 + Pb(NO3)2 -->
PbCl2 + Al(NO3)3
The number of Al
atoms is equal on both sides (both have 1).
Next, there are 3 Cl atoms on the left, 2 on the right.
Lowest common multiple is 6. See coefficients
below.
Both multiply the Cl atoms to 6.
2AlCl3
+ Pb(NO3)2 --> 3PbCl2
+ Al(NO3)3
Next, there is 1 Pb atom on the left, 3 on the right
(because of 3x1).
2AlCl3 + 3Pb(NO3)2
--> 3PbCl2 + Al(NO3)3
Last, check the nitrates (NO3), which now both
have 3 on either side.
This is the same as checking the nitrogens and the
oxygens by themselves.
Answer
to Problem: 2AlCl3
+ 3Pb(NO3)2 --> 3PbCl2 + Al(NO3)3
Note: Printing this out
might help.