Lesson 23: Predicting Grams of Product Produced in a Reaction
(See pages 306-307)
In the last lesson, you learned how to set up a stoichiometry problem to help you predict how many moles of a
product you could make from a given amount of ingredient. You learned how to first write the reaction, balance it, box
the components in the reaction in which you were interested, find the mole ratio and finally apply the ratio to the given
amount of ingredient/reactant in the reaction to predict the number of moles produced by the reaction.
In this lesson, we will go one step further. Instead of stopping with the amount of moles produced by a reaction, we
will calculate how many grams we can produce from the reaction. Of course, first we will have to determine how many
moles of product are made by the reaction. Then we will convert that answer in moles to grams.
Let's look at an example from the last lesson (#22).
Example 1: Suppose you had 10 moles 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 10 moles decomposes?
This was our solution to this example:
NH4NO3
Ratio
2H2O + N2
1:2
10 moles of NH4NO3
20 moles of H2O
We found that 20 moles of H20 could be produced in this reaction. In this lesson we will take the process one step
further. Knowing you could make 20 moles of water is indeed useful, but knowing how many grams of water produced
would be even more useful!
Let's look at how you might go about this. Recall from Lesson 17 where you learned how to convert moles of a
compound into grams of a compound (finding the formula weight). You learned that the atomic mass values found on
the periodic table of elements told you how many grams one mole of a particular element weighed. We will use this
same process to convert moles of a product to grams of a product.
In this example, the reaction produced 20 moles of water. In order to convert these moles of water into grams, first
we must find the formula weight of water (the number of grams in one mole of water). Once we know the formula
weight, we simply multiply that by the number of moles produced. In other words, if one mole of water weighs "this
much," then 20 moles must weigh 20 times "that much."
So, let's find the formula weight of water (H2O)
H: 2 moles hydrogen x 1.01 grams hydrogen/mole hydrogen = 2.02 grams
O: 1 mole oxygen x 16.0 grams oxygen/mole oxygen
= 16.0 grams
= 18.0 grams H2O
From these calculations, we can say that one mole of water weighs 18.0 grams. So, now we multiply the number of
moles produced in the reaction time 18 grams.
20 moles H2O x 18.0 grams H2O/mole H2O = 360 grams H2O
So, from our reaction we can say that 20 moles of water were produced which is equivalent to 360 grams of water.
Let's look at another example: Barium oxide and carbon dioxide react to produce barium carbonate. If you begin with
5.00 moles of barium oxide, how many grams of barium carbonate can you produce from this reaction?
Write the balanced equation here:
The moles ratio is:
From the 5 moles of barium oxide, _________ moles of barium carbonate are produced.
Now, we need to determine the formula weight of barium carbonate. Do that here:
Ba:
x
=
C:
x
=
O:
x
Formula weight
=
=
So, in our reaction we produced _______ moles of barium carbonate. We take moles we produced x the formula
weight of barium carbonate:
_______________ x ________________ = ________________
Check your work by looking at the answers here:
Balanced equation:
BaO + CO2
BaCO3
Mole ratio: 1: 1
5 moles BaO
5 moles Ba(CO3)
Formula weight of Ba (CO3) = 197 grams
5 moles Ba(CO3) x 197 grams/mole = 985 grams Ba(CO3)
To review this process, first we:

Wrote and balanced the chemical equation

Then we determined the mole ratio

Next we applied the mole ratio to the reactant in question to find the number of moles produced

And, finally, we found the number of grams per mole of the product (formula weight) and multiplied it by the
number of moles produced
Predicting Grams Produced from a Given Amount of Ingredient
1. When hydrogen sulfate and sodium cyanide are mixed, hydrogen cyanide and sodium sulfate are the produced. If you
begin with 25.0 moles of sodium cyanide, how many grams of sodium sulfate might you produce from the reaction?
2. Zinc oxide and hydrochloric acid react to produce zinc chloride and water. If you begin with 14.0 moles of zinc oxide,
how many grams of zinc chloride will you produce from this reaction?
3. Carbon and aluminum oxide react to produce aluminum and carbon dioxide (CO2), If you have 1.40 moles of carbon,
how many grams of aluminum might you expect to generate from this reaction?
4. When hydrogen gas and iodine gas are mixed, hydrogen iodide is produced. If you began with 74.0 moles of hydrogen
gas, how many grams of hydrogen iodide will you potentially produce from this reaction?
5. Barium carbonate is the product of the reaction between barium oxide and carbon dioxide. If you begin 0.400 moles
of barium oxide, how many grams of barium carbonate could you produce from this reaction?