Limiting Reactants Notes

The Limiting Reactants interactive is an adjustable-size file that displays nicely on tablets such as the iPad, on Chromebooks, and on laptops and desktops. It's use on phones is at best questionable. The size of the Interactive can be scaled to fit the device that it is displayed on. The compatibility with iPads, other tablets, and Chromebooks make it a perfect tool for use in a 1:1 classroom.

As teachers, we are very familiar with the student perils of stoichiometry. And because of student difficulties with basic stoichiometry, we often skip the topic of limiting/excess reactants. This simulation offers help with understanding basic mole-mole relationships for both stoichiometric and non-stoichiometric conditions. By definition, all reactions involve at least one limiting reactant. But some reactions are performed under conditions in which there is one reaction that limits the yield of products and the other reactant(s) is in excess. This simulation allows a student to explore both sets of conditions, but the real design was to assist students in understanding excess reactant situations.

The simulation includes 8 different chemical reactions that can be explored, accessed from the navigation panel along its left-hand side. The reactions each have a unique set of coefficients. A coefficient ratio is reported for each reaction in the format "x : y" where x and y are the coefficients of the first and the second listed reactant in the chemical equation. Students can easily adjust the number of moles of each reactant that will be added to the reaction chamber. Moles can be varied from 10.0 mol to 200.0 mol. As adjustments are made, a field labeled Availability Ratio is updated. It is expressed in the same "x : y" format; the coefficient of lowest value is one of the numbers - x or y, depending on the reaction. This formatting allows students to easily compare the availability ratio to the coefficient ratio. It is also allows students to compare stoichiometric conditions (availability ratio = coefficient ratio) and non-stoichiometric conditions (availability ratio ≠ coefficient ratio).

A reaction trial can be run by a tap on the Start button. The speed at which a trial proceeds can be controlled using the Sim Speed slider in the top left of the simulation. We recommend the slowest speeds at first. As the reaction proceeds, there are two displays of value. A bar chart with numerical value fields shows the amount of reactants decreasing and the amount of product(s) increasing. The numerical values change by an amount equal to the coefficients when the Sim Speed is set to 1. For a Sim Speed of 2 or 4, the change amounts are two times and four times the coefficients of the chemical equation. A second display of value is the ICE Chart. Here for this topic, ICE stands for Initial, Change, and Ending amounts of reactants and products. The Change Amount fields are updated in real time as the reaction proceeds. Changes occur at 1-second intervals. When one of the reactants depletes, the Ending Amount row is filled in. Viewing the bar charts and the ICE Table along with the Availability Ratio and the Coefficient Ratio enhances student understanding of the concept of a limiting reactant and an excess reactant.

Classrooms can simply open the Interactive and explore the ideas. Or if desired, The Physics Classroom has prepared a student activity sheet for a more directed experience. The activity focuses student attention on the key concepts that the simulation was designed to reinforce. View Activity Sheet.

Our Limiting Reactant simulation is now available with a Concept Checker that coordinates closely with our Activity Sheet. Do the simulation with the help of the Activity Sheet. Process the activity with the class. Then follow it up with the Concept Checker. While the Concept Checker is available to all, student progress is saved for classrooms with a Task Tracker subscription; this allows students to begin the Concept Checker in class and to pick up on where they left off at a later time if they do not finish in class. View Concept Checker.

There are numerous activities and resources on our website that would complement this activity, supporting studies of stoichiometry in general and specifically, limiting/excess reactants. Here are a few you may be interested in:

Chemistry Tutorial: Stoichiometry Chapter, Lesson 3
Non-Stoichiometric Conditions || Solving Limiting Reactant Problems || Determining the Excess Amount
(Many of the earlier pages, prior to Lesson 3, would be good starting points for students having difficulty with Stoichiometry.)

Concept Builders:
Concept Builders typically consist of three scaffolded activities that interactively lead the student to an understanding of a concept or skill. Our Stoichiometry section includes several Concept Builders that would coordinate with the Limiting Reactants simulation and any study of stoichiometry. Many of the activities utilize a table for organizing answers; the table helps students to see the relationships between quantities. Here are a few of our suggestions:

Science Reasoning Center: Stoichiometry
Our interactive Stoichiometry science reasoning activity consists of five activities that center around the concept of atom and mass conservation. Calculations are involved but the answers are not ends in themselves. The role of all calculations is to demonstrate that the concept that if atoms are conserved in a chemical reaction, then it makes sense that mass is conserved. This concept is approached from a variety of angles. Every calculation is accompanied by a follow-up, sense-making question. The activity aligns with the HS-PS1-7 performance expectation of the Next Generation Science Standards.


Calculator Pad: Stoichiometry Chapter
The Calculator Pad is our go-to location for solving word problems in Chemistry. Problems have random numerals, provided automated feedback, and offer opportunities for correction. We currently have 16 stoichiometry problem sets, each with a unique emphasis and difficulty level. There are several problems in each set. We are confident that teachers will find a problem set that is perfect for their need. The problems sets are free for use. Student progress is saved for classes that have subscribed to Task Tracker.