Question

What is an example of a stoichiometry practice problem?

Answer 1

A stoichiometry problem would entail using a balanced chemical equation and mole and mass conversion factors in an attempt to
calculate the amounts of substances involved in a chemical reaction.

Let's take a basic example of a mass to mass stoichiometry problem.

Nitrogen gas and hydrogen gas are combined to form ammonia. What mass of ammonia can be produced from a 10.00 gram sample of nitrogen is combined with an excess of oxygen.

First we must write out a balanced chemical reaction for the process.

`N_2 + 3H_2 -> 2NH_3`

Next we must determine what is known and what we want to find.

10.00 grams `N_2` `->` ? grams of `NH_3`

Now we create a roadmap for the process.

grams `N_2` `->` moles `N_2` `->` moles `NH_3` `->` grams `NH_3`

Then we find the molar mass of the substances.

`N_2` = 2 x 14.01 = 28.02 g/mol `N_2`
`NH_3` = 1 x 14.01 + 3 x 1.01 = 17.04 g/mol `NH_3`

We follow up with the conversion factors for each change of unit.

10.00 g `N_2` x `(1 mol N_2)/( 28.02 g N_2)` x `(2 mol NH_3)/( 1 mol N_2)` x `(17.04 g NH_3)/( 1 mol NH_3)` =

Calculate the value and cancel the units.

= 12.16 g `NH_3`

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