Dougherty Valley High School Chemistry

Predicting Products/Balancing Equations Online Help

 

Practice Problems Here:

Practice Problem #1

Practice Problem #2

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.