Lesson 24: Predicting Grams of Product from Grams of Reactant
(See pages 306-307)
In the last lesson, you learned how to set up a stoichiometry problem to help you predict how many grams of a
product you could make from a given amount of moles of reactant. In this lesson you will learn how to predict the
amount of grams of product created in a reaction from a given number of grams of reactant.
Lets look at an example:
Example 1: Suppose you had 350 grams of ammonium nitrite. If you allowed this compound to decompose, water
and nitrogen gas would result. How many grams of water might your expect if all 350 grams decomposes?
Begin your problem by writing the balanced chemical equation and locating the compounds in question:
350 grams
? grams
NH4NO2
Ratio
2H2O + N2
1:2
At this point in these types of stoichiometry problems we apply the mole ratio to the reactant in question to allow us
to predict the number of moles (or subsequently grams) produced by the reaction. However, in this problem we cannot
do this. We have been given an amount of reactant in grams (and not in moles). In order to be able to
apply the amount of ingredients to the mole ratio, we must first convert the number of grams we've been given to
number of moles.
In the problem, we've been given 350 grams of ammonium nitrite. In order to convert these grams into moles we
must first find the number of grams in one mole of ammonium nitrite. Hopefully, you remember that finding the
formula weight tells you this answer.
Formula weight of ammonium nitrite:
N: 2 x 14.0 grams/mole = 28.0 grams
H: 4 x 1.01 gram/mole = 4.04 grams
0: 2 x 16.0 grams/ mole = 32.0 grams
Formula weight = 64.0 grams/mole ammonium nitrite
This calculation tells us that in one mole of ammonium nitrite weighs 64.0 grams. Therefore, to find how many moles
this is equivalent to, we can set up the following mathematical relationship:
350 grams ammonium nitrite x 64.0 grams ammonium nitrite = 5.46 moles ammonium nitrite
1 mole ammonium nitrite
What we have
1 mole ammonium nitrate has
a mass of 64.0 grams
Now, that we've converted the grams of reactant we've been given to moles, we can apply it to the mole ratio in the
problem.
The mole ratio is: 1:2
Therefore:
5.46 moles of reactant
10.9 moles of product
Or
5.46 moles NH4(N02)
10.9 moles H20
At this point our answer is 10.9 moles of water. If we look back at our problem, we see that we've been asked to
predict the number of grams of water produced by the reaction. Consequently, we now need to convert our answer in
moles to grams (which is exactly what you learned in the last lesson.)
1 mole of H20 = 18.0 grams
(this was just finding the formula weight of water)
From our problem, we found we produced 10.9 moles of water. Therefore:
10.9 moles H20 x 18.0 grams/mole = 197 grams H20
Hopefully, you've realized that converting our grams of reactant to moles of reactant is a process we've learned earlier.
We are now applying what you learned previously to stoichiometry. This lesson just added an additional step in the
beginning of the problem (convert grams to moles) to the problems found in lesson 23. IN ALL SOICHIOMETRY
PROBLEMS YOU NEED TO WORK WITH MOLES FOR THE RATIO TO WORK SINCE CHEMICAL FORMULAS ARE ALL BASED
ON MOLES.
Let's review the steps we learned in this lesson:

Write and balance the chemical reaction.

Locate compounds in question.

Determine the mole ratio.

Convert given grams of reactant to moles of reactant. Sometimes you will be given moles of reactant (like in
lesson 23). In that case you skip this step because you already have moles of reactant.

Apply moles of reactant to mole ratio to get moles of product.

Convert moles of product to grams of product. If the question asks for moles you can skip this step - you are
done!

Be happy because you've completed the problem!
Predicting Grams Produced from a Given Amount of Grams of Reactant
1. Carbon and aluminum oxide react to produce aluminum and carbon dioxide (C02), Suppose that Tony has 48.0 grams
of carbon, how many grams of aluminum might he expect to generate from this reaction?
2. Zinc oxide and hydrochloric acid react to produce zinc chloride and water. If you begin with 78.0 grams of zinc oxide,
how many grams of zinc chloride will you produce from this reaction?
3. When hydrogen sulfate and sodium cyanide are mixed, hydrogen cyanide and sodium sulfate are the produced.
Suppose Chuck has 100 grams of hydrogen sulfate. How many grams of hydrogen cyanide might he expect to produce
from this reaction?
4. Mary had 456 grams of barium oxide. She knew that barium carbonate is the product of the reaction between barium
oxide and carbon dioxide. If she used all of her barium oxide in the reaction, how many grams of barium carbonate
might she expect to produce?
5. When hydrogen gas and iodine gas are mixed, hydrogen iodide is produced. Sara's boss needed her to prepare some
hydrogen iodide for a procedure they were doing later that day. If Sara had 3000 grams of iodine gas on hand, how
many grams of hydrogen iodide could she make for her boss?