Balancing Chemical Equations

Contributor
PhET Interactive Simulations Project at the University of Colorado (PhET)
Type Category
Instructional Materials
Types
Interactive Simulation
Note
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be “fully aligned,” the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.

Reviews

Description

In this interactive simulation, users adjust the coefficients in an equation while the molecules are depicted in a box above the equation. This allows the users to visualize what the symbols in the chemical equation actually mean. They can count the number and kind of each atom and how a change in the coefficient changes the count of each atom. Once the equation is balanced, a big smiley face appears to indicate that the same number and type of atoms are present in the reactants and the products. In the introductory section, users can access a tool box in order to view a bar chart of each type of atom present in the reactants and products to reinforce the idea of what a balanced equation means. Alternatively, they can view a scale for each type of atom present that balances once the same number of each is reached on the reactant and product sides. After completing three introductory equations, the user can choose to play a game with varying levels of difficulty to reinforce the concepts.

Intended Audience

Learner
Educational Level
  • Middle School
Language
English
Access Restrictions

Free access - The right to view and/or download material without financial, registration, or excessive advertising barriers.

Performance Expectations

MS-PS1-5 Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.

Clarification Statement: Emphasis is on law of conservation of matter and on physical models or drawings, including digital forms, that represent atoms.

Assessment Boundary: Assessment does not include the use of atomic masses, balancing symbolic equations, or intermolecular forces.

This resource appears to be designed to build towards this performance expectation, though the resource developer has not explicitly stated so.

Comments about Including the Performance Expectation
Balanced equations are a symbolic representation of the ratios in which atoms and molecules actually interact. It will be helpful to make explicit the connection between balanced equations and the Law of Conservation of Mass. In other words, the number and type of atoms in the reactants and in the products must be made equal because matter can be neither created nor destroyed. Once the idea that the number and types of atoms before and after a reaction must remain constant, it can then be established that the mass before and after the reaction also must be constant. One could use atomic masses from the periodic table to actually calculate the masses for each atom or molecule on the reactant side and then for the product side to illustrate this point. Even better, carefully collected student data from a chemical reactions lab could be used to either illustrate this point or provide the entry point into the topic… Isn’t it really interesting that the masses of the products and the reactants in your experiment are exactly the same? Why do you suppose that is? Does that always happen? How can we figure that out?

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
The purpose of this simulation is to model the rearrangement of atoms and molecules as they react. In doing so, a student can see clearly that even though the atoms may partner differently after the chemical change, there is still always the same number of the same type of atoms before and after the reaction. If the atoms are present at the conclusion of the reaction, they must have been present at the start of the reaction. If the atoms are present at the start of the reaction, they must also be present at the conclusion of the reaction. In order to complete the activity, engaged students will need to make a prediction and/or describe what will happen to the atoms in the reaction. The model itself does not require this, so a teacher will need to ask for predictions/descriptions, to avoid some students' just randomly pressing buttons. You could mention that a simulation like this is but one type of model used by chemists. Another way to model the same concept would be for the students to each represent the atoms involved. Each student could hold a paper with the element or ion symbol and they can act out the reaction. Other students who are observing can help the student atoms/ions by suggesting how they should rearrange themselves to represent the reactions. The helpers may also point out when additional atoms need to be accounted for in order to represent a balanced chemical equation.

Disciplinary Core Ideas

This resource appears to be designed to build towards this disciplinary core idea, though the resource developer has not explicitly stated so.

Comments about Including the Disciplinary Core Idea
It will be helpful to make explicit the connection between the models representing the atoms involved and the Law of Conservation of Mass. Depending on the level of your students, you may also want to include the relationships among these two variables and the balanced equations. In other words, the number and type of atoms in the reactants and in the products must be made equal because matter can be neither created nor destroyed. Once the idea that the number and types of atoms before and after a reaction must remain constant, it is straightforward to establish that the mass before and after the reaction also must be constant. One could use atomic masses from the periodic table to actually calculate the masses for each atom or molecule on the reactant side and then for the product side to illustrate this point, though this is beyond the assessment boundary for middle school. An interesting thing to note is that the simulation will differentiate between a balanced equation and one that is simplified. In other words, a student will be given feedback that his or her equation is correctly balanced but not simplified if the answer 4HCl = 2H2 + 2Cl2 is submitted. However, if an equation is balanced and simplified, the feedback is simply that the answer is correct, not that it is both balanced and simplified. It will be helpful to point out to students that we use the smallest whole number ratios of coefficients to balance an equation. Students may not even realize that this is the case until they encounter a discrepant event.

Crosscutting Concepts

This resource appears to be designed to build towards this crosscutting concept, though the resource developer has not explicitly stated so.

Comments about Including the Crosscutting Concept
Matter is anything that has mass and takes up space. Although they are incredibly small, atoms have mass and take up space. As such, they are matter. Since the number and type of atoms in a chemical reaction must remain constant before and after the reaction, the amount of matter must also remain constant. This is simply another way of stating that matter is conserved during chemical reactions.

Resource Quality

  • Alignment to the Dimensions of the NGSS: Grade‐appropriate components of the science practice, disciplinary core idea, and crosscutting concept work together to support students in three‐dimensional learning to make sense of balancing chemical reactions. A teacher will need to spotlight the connection between balanced equations and the Law of Conservation of Mass. This resource models conservation of matter at the atomic level, but does not provide an opportunity for students to explore a reaction or phenomena at the macro-level.

  • Instructional Supports: Students are able to explore practicing balancing three reactions to make ammonia, separate water and combust methane. They are able to use a balance or bar graph to help scaffold counting how many of each type of atom are present in the reactants versus products of the reaction. They earn a Smiley Face when successfully balancing the equation. In the "Game" section they are able to see the molecules pictured, but not the bar graph or scales scaffolds. They earn 2 points for a successful first try, and 1 point if they balance the equation on the second try. A teacher may have students show them a score of 9 or 10 before moving on to the next level of the game as a way of checking in with each students' progress. This exercise can be done alone or in pairs, depending on the technology available. Lesson plans related to this resource are available on the resource’s website, and may offer suggestions about incorporating more instructional supports for differentiating instruction to all learners.

  • Monitoring Student Progress: Students are provided with feedback directly with a Smily Face when they successfully balance an equation. The teacher will need to check in with students to see how they are progressing and which scaffolds they are using to help assist in balance equations in the "Game" section. An interesting thing to note is that the simulation will differentiate between a balanced equation and one that is simplified. In other words, a student will be given feedback that his or her equation is correctly balanced but not simplified if the answer 4HCl --> 2H2 + 2Cl2 is submitted. However, if an equation is balanced and simplified, the feedback is simply that the answer is correct, not that it is both balanced and simplified. It will be helpful to point out to students that we use the smallest whole number ratios of coefficients to balance an equation.

  • Quality of Technological Interactivity: The interactivity of the simulation is directly related to the learning goal of balancing equations and visualizing what a balanced equation means. It is well designed and easy to use. Smiley faces, games, and timers help increase motivation while rewarding and entertaining the learner. This simulation can be downloaded for access without the internet (uses Java), but can also be played on an iPad or tablet using the HTML5 version directly from the web browser.