Solving Stoichiometry Problems

stoichiometric ratio example

Core Concepts

In this tutorial, you will learn what is stoichiometry and the different types of problems involving it. You will go through several examples to practice and master the content!

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Stoichiometry Definition

What is Stoichiometry?

Stoichiometry is math having to do with chemical reactions. There are different types of calculations you can perform; stoichiometry with moles is the most common, but you can also do math with masses and even percentages. Read about the origins of stoichiometry here!

Stoichiometric Ratio

A stoichiometric ratio comes into play when talking about the relationships of elements or molecules in specific problems. This is the exact ratio between the coefficients of the reactants and products needed for a reaction to proceed normally. Let’s work through some problems you may see when learning about stoichiometry.

Stoichiometry Problems

Balancing Chemical Equations

A very common type of stoichiometric problem is balancing equations. This is an important chemistry skill to have because you have to have the correct ratio of reactants and products in order for a reaction to proceed; this is also an important foundation for organic chemistry. Although we have a tutorial on balancing equations, let’s look at one example.

Balance the following reaction:

__ C2H2 + __ O2  → __ CO2 + __ H2O

The main idea when balancing equations is that there should be the same number of each element on both sides of the reaction. You can balance the carbons and the hydrogens first, then move onto the oxygen. The balanced equation should look like this:

2C2H2 + 5O2  → 4CO2 + 2H2O

Example – Using Stoichiometric Ratio (Moles)

Use the equation below to solve the problem.

C6H12O6  → 2C2H5OH + 2CO2

If 2.5 moles of C6H12O6 reacts, how many moles of carbon dioxide are produced?

Using dimensional analysis, you can use the stoichiometric ratio to find the solution to this problem. By looking at the coefficients, you can see that for every 1 mole of C6H12O6, 2 moles of CO2 are produced. Using this ratio, you can figure out how many moles of carbon dioxide are made from 2.5 moles of glucose.

stoichiometry example problem

Example – Using Stoichiometric Ratio (Mass)

Let’s use the same equation as the problem above.

C6H12O6  → 2C2H5OH + 2CO2

How many grams of C6H12O6 was initially used if 10g of C2H5OH was produced?

Similar to the previous problem, by using the stoichiometric ratio of reactant to product, you can find the answer. Dimensional analysis is used to go from grams of C2H5OH to molar mass to mole (stoichiometric) ratio and back to grams.

stoichiometry example problem

Further Reading

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