# What is an example of a stoichiometry practice problem?

##### 1 Answer
Sep 26, 2014

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.

${N}_{2} + 3 {H}_{2} \to 2 N {H}_{3}$

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

10.00 grams ${N}_{2}$ $\to$ ? grams of $N {H}_{3}$

Now we create a roadmap for the process.

grams ${N}_{2}$ $\to$ moles ${N}_{2}$ $\to$ moles $N {H}_{3}$ $\to$ grams $N {H}_{3}$

Then we find the molar mass of the substances.

${N}_{2}$ = 2 x 14.01 = 28.02 g/mol ${N}_{2}$
$N {H}_{3}$ = 1 x 14.01 + 3 x 1.01 = 17.04 g/mol $N {H}_{3}$

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

10.00 g ${N}_{2}$ x $\frac{1 m o l {N}_{2}}{28.02 g {N}_{2}}$ x $\frac{2 m o l N {H}_{3}}{1 m o l {N}_{2}}$ x $\frac{17.04 g N {H}_{3}}{1 m o l N {H}_{3}}$ =

Calculate the value and cancel the units.

= 12.16 g $N {H}_{3}$

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