In Greek, stoikhein means element and metron means measure, so stoichiometry literally translated means the measure of elements. In chemistry, chemical reactions are frequently written as an equation, using chemical symbols. The reactants are displayed on the left side of the equation and the products are shown on the right, with the separation of either a single or double arrow that signifies the direction of the reaction.

The significance of single and double arrow is important when discussing solubility constants, but we will not go into detail about it in this module. To balance an equation, it is necessary that there are the same number of atoms on the left side of the equation as the right.

One can do this by raising the coefficients. A chemical equation is like a recipe for a reaction so it displays all the ingredients or terms of a chemical reaction. It includes the elements, molecules, or ions in the reactants and in the products as well as their states, and the proportion for how much of each particle is create relative to one another, through the stoichiometric coefficient.

The following equation demonstrates the typical format of a chemical equation:. In the above equation, the elements present in the reaction are represented by their chemical symbols. Based on the Law of Conservation of Masswhich states that matter is neither created nor destroyed in a chemical reaction, every chemical reaction has the same elements in its reactants and products, though the elements they are paired up with often change in a reaction.

Displaying each element is important when using the chemical equation to convert between elements. In a balanced reaction, both sides of the equation have the same number of elements. The stoichiometric coefficient is the number written in front of atoms, ion and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation.

Though the stoichiometric coefficients can be fractions, whole numbers are frequently used and often preferred. This stoichiometric coefficients are useful since they establish the mole ratio between reactants and products.

In the balanced equation:. This is known as the coefficient factor. The balanced equation makes it possible to convert information about one reactant or product to quantitative data about another element.

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Understanding this is essential to solving stoichiometric problems. The reaction is not balanced; the reaction has 16 reactant atoms and only 14 product atoms and does not obey the conservation of mass principle.JavaScript seems to be disabled in your browser. For the best experience on our site, be sure to turn on Javascript in your browser.

We know what you're thinking. You hate stoichiometry. You can't spell it, you can't pronounce it, and it involves all sorts of calculations that make you go nuts.

Your friends and classmates all hate it, too, and your teacher keeps using the word stoichiometry like it's some sort of magic spell. It's okay. Forget anything you might have heard about stoichiometry because we're going to start from scratch. First things first, what is stoichiometry? The best definition for stoichiometry is the simple one: it's a way to figure out how much stuff you're going to make in a chemical reaction, or how much stuff you'll need to make a chemical reaction do what you want.

When we put it that way, stoichiometry isn't so bad. We can deal with the crazy name if it's that simple. Let's think of one of our favorite chemical reactions: making a cheeseburger. Okay, maybe it's not a chemical reaction, but the concept is the same.

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When we're really hungry and want more than one cheeseburger, we can put our mad stoichiometry skills to use and figure out how much of each ingredient we need. For example, if we want to make four cheeseburgers, we need four buns, four patties, and eight slices of cheese. That is delicious stoichiometry in action. Of course, it's not entirely that simple. To be a master at stoichiometry you also have to be a master at unit conversion.

Once we get through with this guide, you'll want to invite stoichiometry it to all the parties and fun times. Science Geek Stoichiometry Review This website contains a few useful stoichiometry practice problems.

Type in your answers and click submit. You'll soon find out if you're correct. Moles and Stoichiometry Practice Problems Still need some additional practice problems? Check these out… complete with answers at the bottom of the page. Balancing Chemical Equations This website gives tons of practice on balancing chemical equations. Brightstorm Stoichiometry Review Here is a short, but sweet, recap of all things stoichiometry. Need a nice refresher? Stoichiometry Basics Another quick and simple stoichiometry overview.

A little extra help couldn't hurt, right? Stoichiometry Sing-Along Lady Gaga and stoichiometry? Yes, please. Stoichiometry: Concept and Examples This video not only gives a refresher about basic stoichiometry concepts but it also works though many stoichiometry examples. Limiting Reagents Here is a nice video tutorial about all things limiting reagents.

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## Stoichiometry and Balancing Reactions

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### Stoichiometry and Balancing Reactions

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Phosphoric acid is H 3 PO 4. Calculate the percent composition by mass of H, P, and O in this compound. How many grams of Li are needed to produce 7. If How many grams of oxygen are needed to make grams of CO 2? Each isotope contributes to the average atomic mass based on its relative abundance.

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Multiplying the mass of an isotope by its fractional abundance will give the contribution to the average atomic mass of that isotope. We need two conversions: first from grams to moles and then from moles to number of particles atoms. The conversion factor is:.

To calculate molecular mass, we need to sum all the atomic masses in the molecule. For each element, we multiply the atomic mass of the element by the number of atoms of that element in the molecule. We can find the atomic masses on the periodic table. There are eight C atoms, ten H atoms, four N atoms, and two O atoms in caffeine, so the molecular mass is given by:.

How many hydrogen atoms are present in Assume that you have 1 mole of H 3 PO 4. The percent by mass of each element is given by the combined molar mass of the atoms of the element in 1 mole of H 3 PO 4 divided by the molar mass of H 3 PO 4then multiplied by percent.

Terms of Use and Privacy Policy. Already have an account? Log in. Stoichiometry is the method used to relate the quantities of substances in chemical equations. It is useful because with the quantity of just one substance in the equation, you can learn something about the quantities of all other substances in that equation.

A limiting reactant is the reactant in a chemical equation that runs out first. It is important because its quantity determines the amount of products produced. Gay Lussac's Law says that the stoichiometric coefficients in a chemical equation relate the volume of gases in that equation as well as the number of moles. It can be used to relate the quantities of gaseous substances in a chemical equation if those quantities are given in volume units. Get started today!

Apologia Chemistry Module 8 Study Guide. Edit a Copy. Study these flashcards. Addie C. Define stoichiometry and explain why it is such a useful tool for chemists. Explain what a limiting reactant is and why it is important in stoichiometry.

State Gay-Lussac's Law and explain how it is used. If a stoichiometry problem gives you the quantity of a substance in grams, what is the first thing you must do to solve the problem? Since stoichiometry can only be done in moles or volumes in the case of gasesthe first thing you must do is convert to moles.

This conversion must be done because the ratio from the balanced chemical equation is in moles. What is the difference between molecular formulas and empirical formulas? Molecular formulas provide the exact number of each type of atom in the molecule.The atomic ratios in each compound are also the relative number of atomic mass units of its elements.

The first example is nitrous oxide N 2 Oas shown in Table 1. The relative masses were obtained by multiplying the atomic ratios and atomic masses. You can see that a sample of N 2 O weighing The mass percent of each element is calculated from its relative mass divided by the sum of the relative masses. Chemical compounds with integral atomic ratios, like nitrous oxide, are described as stoichiometric compounds, and they permit many simple calculations. The common oxide of aluminum provides a second example, but this time, begin with the mass percent and deduce the atomic ratio. Careful laboratory analysis of aluminum oxide determines it to be approximately 53 percent aluminum and 47 percent oxygen by mass, as shown in the second column in Table 2. The relative masses are obtained by dividing the mass percentages by the atomic masses from the periodic table.

This ratio of integers implies that the formula for aluminum oxide is A1 2 O 3. In simple compounds, the metallic elements are written before the nonmetals. Most chemical compounds are stoichiometric, and you should be able to utilize the atomic masses and perform the following calculations:. These calculations are so basic to the field that you should go back and carefully review the two examples in this section: the calculation of mass percents in N 2 O and the inference of the formula for aluminum oxide.

Then you can practice stoichiometric calculations on the following pair of problems, which are answered and explained in the. Previous Quiz Chemical Compounds. Next Quiz Stoichiometry. Removing book from your Reading List will also remove any bookmarked pages associated with this title.

### Stoichiometry

Are you sure you want to remove bookConfirmation and any corresponding bookmarks? My Preferences My Reading List. Home Study Guides Chemistry Stoichiometry. Adam Bede has been added to your Reading List!During these challenging times, we guarantee we will work tirelessly to support you.

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We will get through this together. In a chemical reaction, matter can neither be created nor destroyed according to the law of conservation of mass, so the products that come out of a reaction must equal the reactants that go into a reaction.

This means the same amount of each atom that you put in must come back out. Stoichiometry is the measure of the elements within a reaction. Stoichiometry is one half math, one half chemistry, and revolves around the one simple principle above - the principle that matter is never lost or gained during a reaction. The first step in solving any chemistry problem is to balance the equation. To do stoichiometry, start by balancing the chemical equation so that the number of atoms on each side of the equal sign are exactly the same. Next, convert the units of measurement into moles and use the mole ratio to calculate the moles of substance yielded by the chemical reaction. Then, convert moles of wanted substance to the desired units of measurement!

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