Rotate to landscape screen format on a mobile phone or small tablet to use the Mathway widget, a free math problem solver that answers your questions with step-by-step explanations.
We welcome your feedback, comments and questions about this site or page. Please submit your feedback or enquiries via our Feedback page. The following Stoichiometry Road Map gives a summary of how to use stoichiometry to calculate moles, masses, volumes and particles in a chemical reaction with limiting and excess reactants. Scroll down the page for more examples and solutions. Stoichiometry - Limiting and Excess Reactant Introduction to Limiting Reactant and Excess Reactant The limiting reactant or limiting reagent is the first reactant to get used up in a chemical reaction.
Once the limiting reactant gets used up, the reaction has to stop and cannot continue and there is extra of the other reactants left over. Those are called the excess reactants. We will learn about limiting reactant and limiting reagent by comparing chemical reactions to cooking recipes and we will look at an actual stoichiometry problem.
Example: What is the greatest amount of NH 3 in moles that can be made with 3. What is the limiting reactant? Which reactant is in excess and how many moles of it are left over?
You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.How much equipment do you need for an experiment?
You are in charge of setting out the lab equipment for a chemistry experiment. If you have twenty students in the lab and they will be working in teams of two and the experiment calls for three beakers and two test tubes, how much glassware do you need to set out?
Figuring this out involves a type of balanced equation and the sort of calculations you would do for a chemical reaction. You have learned about chemical equations and the techniques used in order to balance them.
Chemists use balanced equations to allow them to manipulate chemical reactions in a quantitative manner. Our ham sandwich is composed of 2 slices of ham Ha slice of cheese Ca slice of tomato T5 pickles Pand 2 slices of bread B. The equation for our sandwich is shown below:. Now let us suppose that you are having some friends over and need to make five ham sandwiches. How much of each sandwich ingredient do you need? You would take the number of each ingredient required for one sandwich its coefficient in the above equation and multiply by five.
Using ham and cheese as examples and using a conversion factor, we can write:. The conversion factors contain the coefficient of each specific ingredient as the numerator and the formula of on sandwich as the denominator. The result is what you would expect. In order to make five ham sandwiches, you would need 10 slices of ham and 5 slices of cheese. This type of calculation demonstrates the use of stoichiometry. Stoichiometry is the calculation of the amount of substances in a chemical reaction from the balanced equation.
The sample problem below is another stoichiometry problem involving ingredients of the ideal ham sandwich. Kim looks in the refrigerator and finds that she has 8 slices of ham. In order to make as many sandwiches as possible, how many pickles does she need?
Use the equation above. Step 1: List the known quantities and plan the problem. The coefficients for the two reactants ingredients are used to make a conversion factor between ham slices and pickles. Since 5 pickles combine with 2 ham slices in each sandwich, 20 pickles are needed to fully combine with 8 ham slices. Step 3: Think about your result. The 8 ham slices will make 4 ham sandwiches.
Stoichiometry - Limiting and Excess Reactant
With 5 pickles per sandwich, the 20 pickles are used in the 4 sandwiches. Use the link below to answer the following questions:. What does this porch need? You want to add some sections to the porch seen above. Before you go to the hardware store to buy lumber, you need to determine the unit composition the material between two large uprights.
You count how many posts, how many boards, how many rails — then you decide how many sections you want to add before you calculate the amount of building material needed for your porch expansion.
Stoichiometry problems can be characterized by two things: 1 the information given in the problem, and 2 the information that is to be solved for, referred to as the unknown.
The given and the unknown may both be reactants, both be products, or one may be a reactant while the other is a product. The amounts of the substances can be expressed in moles. However, in a laboratory situation, it is common to determine the amount of a substance by finding its mass in grams.
The amount of a gaseous substance may be expressed by its volume. In this concept, we will focus on the type of problem where both the given and the unknown quantities are expressed in moles.
Chemical equations express the amounts of reactants and products in a reaction.Stoichiometry is the study of the relative quantities of reactants and products in chemical reactions and how to calculate those quantities. Chemical equations are symbolic representations of chemical reactions. The reacting materials reactants are given on the left, and the products are displayed on the right, usually separated by an arrow showing the direction of the reaction. The numerical coefficients next to each chemical entity denote the proportion of that chemical entity before and after the reaction.
The law of conservation of mass dictates that the quantity of each element must remain unchanged in a chemical reaction. Therefore, in a balanced equation each side of the chemical equation must have the same quantity of each element. Chemical equations : A chemical equation shows what reactants are needed to make specific products.
Reactions are balanced by adding coefficients so that there are the same number of atoms of each element on both sides of the reaction. Stoichiometry is the field of chemistry that is concerned with the relative quantities of reactants and products in chemical reactions.
For any balanced chemical reaction, whole numbers coefficients are used to show the quantities generally in moles of both the reactants and products.
For example, when oxygen and hydrogen react to produce water, one mole of oxygen reacts with two moles of hydrogen to produce two moles of water. In addition, stoichiometry can be used to find quantities such as the amount of products that can be produced with a given amount of reactants and percent yield. Upcoming concepts will explain how to calculate the amount of products that can be produced given certain information.
The relationship between the products and reactants in a balanced chemical equation is very important in understanding the nature of the reaction. This relationship tells us what materials and how much of them are needed for a reaction to proceed.
Reaction stoichiometry describes the quantitative relationship among substances as they participate in various chemical reactions. Molar ratios, or conversion factors, identify the number of moles of each reactant needed to form a certain number of moles of each product. In a chemical equation, the reacting materials are written on the left, and the products are written on the right; the two sides are usually separated by an arrow showing the direction of the reaction.
The numerical coefficient next to each entity denotes the absolute stoichiometric amount used in the reaction. Because the law of conservation of mass dictates that the quantity of each element must remain unchanged over the course of a chemical reaction, each side of a balanced chemical equation must have the same quantity of each particular element.
In a balanced chemical equation, the coefficients can be used to determine the relative amount of molecules, formula units, or moles of compounds that participate in the reaction. The coefficients in a balanced equation can be used as molar ratios, which can act as conversion factors to relate the reactants to the products. These conversion factors state the ratio of reactants that react but do not tell exactly how much of each substance is actually involved in the reaction.
The molar ratios identify how many moles of product are formed from a certain amount of reactant, as well as the number of moles of a reactant needed to completely react with a certain amount of another reactant. For example, look at this equation:. In other words, 1 mol of methane will produced 1 mole of carbon dioxide as long as the reaction goes to completion and there is plenty of oxygen present.
These molar ratios can also be expressed as fractions. These molar ratios will be very important for quantitative chemistry calculations that will be discussed in later concepts.Worksheet 1 Stoichiometry. Calculate the mass of carbon required to consume 5. Calculate the amount of oxygen in grams produced by the reaction of Calculate the theoretical yield in grams of Fe produced by the reaction of 5.
Calculate the number of moles CO 2 produced by the reaction of 8. Calculate the number of Fe atoms consumed in the reaction if Calculate the number of grams water produced by the complete reaction of Calculate the mass of carbon required to produce 5. Calculate the amount of oxygen in grams produced by the reaction of g of water. Calculate the theoretical yield in grams of CO 2 produced by the reaction of Calculate the number of molecules of CO 2 produced by the reaction of 2.
STP is standard temperature and pressure, which is, 0 o C and Kpa. To calculate the molar mass, divide the number of litres by the number of moles. Weigh a 3. Add about 10 mL of concentrated HCl to a gas collecting tube. Caution: HCl is very corrosive! Carefully pour water over the HCl to fill the gas collecting tube.
Fill a mL beaker to mL with water. Roll the magnesium into a coil that is small to fit into the gas collecting tube. Place it into the tube and allow it to sink down to the acid. When it reaches the acid it will begin to bubble and rise. As soon as it begins to rise, place your thumb on the top of the tube to completely seal the opening, invert the tube and place under the water in the ml beaker.
Remove your thumb as soon as the tube is under the surface of the water. Clamp the tube to a ring stand to secure it. After the reaction is over allow five minutes for the hydrogen gas to reach room temperature. Record the volume of the hydrogen gas. Clean and put away all of your equipment.
Wash your lab bench. Write a balanced single replacement equation for the reaction between HCl and Mg. Covert grams Mg into moles H 2 at room pressure and temperature.
Convert the volume of H 2 in litres to STP conditions by multiplying by the conversion factor 0.
Stoichiometry - Limiting and Excess Reactant
Calculate the molar volume by dividing the volume of H 2 in litres by the number of mole H 2. Determine an accepted value from your textbook for the molar volume of a gas at STP. Calculate the percentage difference between the accepted value and the experimental value of the molar volume.
STP Calculations. Calculate the volume of F 2 gas at STP produced by the electrolysis of 8.
Chapter 12.2: Stoichiometry of Reactions in Solution
Calculate the mass of KF required to produce Quantitative calculations involving reactions in solution are carried out in the same manner as we discussed in Chapter Instead of masseshowever, we use volumes of solutions of known concentration to determine the number of moles of reactants. Whether we are dealing with volumes of solutions of reactants or masses of reactants, the coefficients in the balanced chemical equation tell us the number of moles of each reactant needed and the number of moles of each product that can be produced.
An expanded version of the flowchart for stoichiometric calculations illustrated in Figure We can use the balanced chemical equation for the reaction and either the masses of solid reactants and products or the volumes of solutions of reactants and products to determine the amounts of other species, as illustrated in Example 7, Example 8, and Example 9. Figure The balanced chemical equation for a reaction and either the masses of solid reactants and products or the volumes of solutions of reactants and products can be used in stoichiometric calculations.
Gold is then recovered by reduction with metallic zinc according to the following equation:. What mass of gold would you expect to recover from Given: chemical equation and molarity and volume of reactant. Asked for: mass of product.
A Check the chemical equation to make sure it is balanced as written; balance if necessary. B From the balanced chemical equation, use a mole ratio to calculate the number of moles of gold that can be obtained from the reaction.
To calculate the mass of gold recovered, multiply the number of moles of gold by its molar mass. A The equation is balanced as written, so we can proceed to the stoichiometric calculation. We can adapt Figure The problem asks for the mass of gold that can be obtained, so we need to convert the number of moles of gold to the corresponding mass using the molar mass of gold:.
We can also modify the table method using the volume and the molarity to calculate the number of moles. The concept of limiting reactants applies to reactions that are carried out in solution as well as to reactions that involve pure substances.
If all the reactants but one are present in excess, then the amount of the limiting reactant may be calculated as illustrated in Example 8. Because the consumption of alcoholic beverages adversely affects the performance of tasks that require skill and judgment, in most countries it is illegal to drive while under the influence of alcohol.
In almost all US states, a blood alcohol level of 0. Higher levels cause acute intoxication 0. The reaction used in the Breathalyzer is the oxidation of ethanol by the dichromate ion:. When a measured volume A typical Breathalyzer ampul contains 3. How many grams of ethanol must be present in Given: volume and concentration of one reactant.
Asked for: mass of other reactant needed for complete reaction. A In any stoichiometry problem, the first step is always to calculate the number of moles of each reactant present. In this case, we are given the mass of K 2 Cr 2 O 7 in 1 mL of solution, which we can use to calculate the number of moles of K 2 Cr 2 O 7 contained in 1 mL:.A balanced chemical equation gives the identity of the reactants and the products as well as the accurate number of molecules or moles of each that are consumed or produced.
Stoichiometry A collective term for the quantitative relationships between the masses, the numbers of moles, and the numbers of particles atoms, molecules, and ions of the reactants and the products in a balanced chemical equation. A stoichiometric quantity The amount of product or reactant specified by the coefficients in a balanced chemical equation.
In Section This section describes how to use the stoichiometry of a reaction to answer questions like the following: How much oxygen is needed to ensure complete combustion of a given amount of isooctane? This information is crucial to the design of nonpolluting and efficient automobile engines. How many grams of pure gold can be obtained from a ton of low-grade gold ore? The answer determines whether the ore deposit is worth mining.
If an industrial plant must produce a certain number of tons of sulfuric acid per week, how much elemental sulfur must arrive by rail each week?
Unit 4 - Stoichiometry
All these questions can be answered using the concepts of the mole and molar and formula masses, along with the coefficients in the appropriate balanced chemical equation.
When we carry out a reaction in either an industrial setting or a laboratory, it is easier to work with masses of substances than with the numbers of molecules or moles. We will first present the method used in most other books for converting from the mass of any reactant or product to the mass of any other reactant or product using a balanced chemical equation outlined in Figure We will then show how this can be simplified by into a tabular algorithm.
The key to everything is to start with a balanced chemical reaction. Converting amounts of substances to moles—and vice versa—is the key to all stoichiometry problems, whether the amounts are given in units of mass grams or kilogramsweight pounds or tonsor volume liters or gallons.
Figure We saw earlier that glucose reacts with oxygen to produce carbon dioxide and water:. Just before a chemistry exam, suppose a friend reminds you that glucose is the major fuel used by the human brain. If a typical 2 oz candy bar contains the equivalent of The initial step in solving a problem of this type must be to write the balanced chemical equation for the reaction.
Inspection of Equation Use the molar mass of glucose to one decimal place, According to the balanced chemical equation, 6 mol of CO 2 is produced per mole of glucose; the mole ratio of CO 2 to glucose is therefore If we divide the number of moles of CO2 by its stoichiometric coefficient 6 and the number of moles of glucose by its stoichiometric coefficient of one the ratios, which can be called the reaction equivalents, are equal.How To: Find Limiting Reagent (Easy steps w/practice problem)
We will use this below in demonstrating another method of solving stoichiometric problems of all types. The number of moles of CO 2 produced is thus. Use the molar mass of CO 2 Discrepancies between the two values are attributed to rounding errors resulting from using stepwise calculations in steps 1—3. In Chapter 6you discovered that this amount of gaseous carbon dioxide occupies an enormous volume—more than 33 L.
We could use similar methods to calculate the amount of oxygen consumed or the amount of water produced. We just used the balanced chemical equation to calculate the mass of product that is formed from a certain amount of reactant. We can also use the balanced chemical equation to determine the masses of reactants that are necessary to form a certain amount of product or, as shown in Example There is another way of dealing with such problems which is easier to carry out.
It starts by writing the balanced chemical equation and then drawing a table with five rows and as many columns as there are reactants and products and writing in the given mass.
We then simply fill in the stoichiometric coefficients and the molecular weights of the reactants and the products that we are concerned with. Divide the mass of the glucose by the molecular weight to find the number of moles of glucose. In the next step divide the number of moles by the stoichiometric coefficient to find the stoichiometric equivalents this is the same as step 2a above. The rule is to divide going down the table.Brewer's Brainiacs Search this site.
Home Page. AP Chemistry. Integrated Chemistry. Pre AP Chemistry. Everything we've done so far has been to prepare you for this unit.
If you are still struggling with balancing equations, I have added a practice worksheet below called Practicing Word Equations. The answer key is attached, so don't scroll to the end until you have tried it first.
You might also want to go online and practice at one of the many interactive websites. I've also added a worksheet for more limiting reactants practice. The answer key is not attached but is on my whiteboard at school. The moles unit set you up to use the mole map to do conversions. I've included a copy of the mole map below. The mole pattern is also included below for anyone who has lost theirs.
Class Schedule. Homework Schedule. Limiting 2 worksheet. Valerie Brewer, Dec 10,PM. Practice Limiting Reactants Worksheet. Valerie Brewer, Dec 11,AM. Practicing Word Equations for stoic. Valerie Brewer, Dec 3,PM. StoichReview v. Valerie Brewer, Jan 31,PM. Valerie Brewer, Dec 3,AM. Valerie Brewer, Jan 13,AM. Valerie Brewer, Jan 17,PM. Valerie Brewer, Jan 23,PM.
Valerie Brewer, Feb 1,PM. As always, you can find homework worksheets below.