Lesson 7. Lesson 7: Introduction to Balancing Chemical Equations

Carole Namowicz
Chemistry
100 min
High School Honors Chemistry
v2

Overview

This lesson is a continuation of Lesson 6: Limiting Reactants Dictate Molar Relationships. It connects the ideal ratio that left no excess reactants to coefficients used to balance and equations. Students need to realize that balanced equations don’t "waste" anything. Students will learn the term coefficient and how to use an atom inventory to determine if a chemical equation is balanced or not. Then they will use the balancing simulation. They will complete the introduction first before moving on to the game portion.

Standards

Next Generation Science Standards
  • Physical Science
  • NGSS Practice
    • Using Mathematics
  • NGSS Crosscutting Concept
    • Energy
Computational Thinking in STEM
  • Data Practices
    • Analyzing Data
  • Modeling and Simulation Practices
    • Assessing Computational Models
    • Using Computational Models to Understand a Concept
  • Systems Thinking Practices
    • Defining Systems and Managing Complexity
    • Thinking in Levels
    • Understanding the Relationships within a System

Credits

Unit designed by Carole Namowicz a teacher at Lindblom.

Activities

  • 1. Review
  • 2. Balancing
  • 3. Why Balance?
  • 4. Introduction
  • 5. The Simulation
  • 6. The Game

Student Directions and Resources


This simulation will help you to visualize the process of balancing equations. You will begin with the Introduction where you will go through the process of balancing three different equations. After you finish the Introduction, you will proceed to the Game which is broken down into three levels. Each level has five equations to balance.

1. Review


In the previous lesson, you observed a chemical reaction with magnesium (Mg) and hydrochloric acid (HCl) that produced magnesium chloride (MgCl2) and hydrogen gas (H2). This chemical reaction is represented as a chemical equation below.

Mg + HCl  ----->   MgCl2    +   H2 
bracket   bracket
Reactants   Products
 
If the correct proportions of magnesium and hydrochloric acid were utilized in the chemical reaction, all of the starting magnesium was used, and that with the hydrochloric acid yielded the maximum amount of hydrogen gas possible. If the wrong ratio of magnesium to hydrochloric acid was used, then some magnesium remained after the reaction was complete and the maximum amount of hydrogen gas was NOT produced. The chemical equation as represented above is a 1:1 ratio of Mg to HCl which did NOT use all of the magnesium and produce the maximum amount of hydrogen gas.

Question 1.1

1. What was the correct ratio of Mg to HCl that used all of the magnesium and produced the maximum amount of hydrogen gas possible?

  A) A 2:1 ratio of magnesium to hydrochloric acid
  B) A 1:2 ratio of magnesium to hydrochloric acid
  C) A 2:2 ratio of magnesium to hydrochloric acid
  D) A 1:3 ratio of magnesium to hydrochloric acid


2. Balancing


In order to use all of the starting magnesium and produce the maximum amount of hydrogen gas possible, a 1:2 ratio of magnesium to hydrochloric acid is needed. This is represented in the chemical equation below by adding a coefficient in front of the HCl.

             

  Mg 

+

 2 HCl

 -----> 

 MgCl2 

 + 

 H2

  
       
Coefficient                   

 

Coefficients tell you how many moles of each chemical are needed for the reaction to take place most efficiently. If there is no coefficient present, then it is assumed to be 1. For the reaction above, you will need 1 mole of Mg with 2 moles of HCl to yield 1 mole of MgCl2 and 1 mole of H2.

3. Why Balance?


In Lesson 2, "What Happens to Mass in a Chemical Reaction?" you learned about the law of conservation of mass. Recall that the law of conservation of mass states that matter (mass) cannot be created or destroyed. Therefore the total mass of the reactants in a chemical reaction must be equal to the total mass of the products. Chemical reactions represent different quantities or amounts of reactants and products using coefficients. Adding the coefficients insures equal masses on both sides of the equation; this process is known as balancing an equation.

The chemical reaction shown below is unbalanced, that is, it does not follow the law of conservation of mass.

 Mg   +    HCl    ----->   MgCl2    +   H2 

 

We can determine the reaction is unbalanced by performing an atom inventory. An atom inventory is counting different types of atoms on both sides of the equation to see if they are equal. An atom inventory for the equation is shown below.

Mg + HCl  ----->   MgCl2    +   H2 
                   1    Mg    1  
  1    H    2  
  1    Cl    2  

 

In order to balance the equation, we added a coefficient of 2 in front of the hydrochloric acid (HCl). The updated atom inventory is shown below.

Mg + 2 HCl  ----->   MgCl2    +   H2 
                   1    Mg    1  
  2     1    H    2  
  2     1    Cl    2  
 
Notice now all elements have equal numbers of atoms on both the reactants and products side of the equation. This equation is now considered to be balanced.

4. Introduction


On the next screen, you will use a simulation in order to balance several chemical reactions. All reactions will be presented with no coefficients (understood to be a coefficient of 1). You will be able to adjust coefficient numbers up and down as you observe scales that represent the atom inventory for all atoms present in the reaction. The reaction is balanced when all the scales are balanced.

5. The Simulation


  1. Select Introduction
  2. Refresh the page if you need to start over for any reason.
  3. Notice the "Tools" menu in the upper right. Experiment with the balance and the bar graph to determine if either tools option helps you to visualize the balancing process.
  4. The three reactions you will balance are at the bottom of the screen.
  5. Use the arrows next to the compounds to change the coefficients.
  6. You must keep working until you get the smiley face above the equals sign to appear.

 


Question 5.1

1. Balance the formula for "Make Ammonia". What are the correct coefficients to balance the chemical equation?

____ N2 + ____ H2 → ____ NH3
 

  A) 2, 3, 2
  B) 1, 2, 3
  C) 3, 2, 1
  D) 1, 3, 2


Question 5.2

2. Balance the formula for "Separate Water". What are the correct coefficients to balance the chemical equation?

____ H2O → ____ H2 + ____ O2

  A) 1, 2, 1
  B) 1, 2, 2
  C) 1, 1, 2
  D) 2, 2, 1


Question 5.3

3. Balance the formula for "Combust Methane". What are the correct coefficients to balance the chemical equation?

____ CH4 + ____ O2 → ____ CO2 + ____ H2O

  A) 1, 2, 1, 2
  B) 1, 2, 2, 4
  C) 2, 2, 2, 4
  D) 4, 2, 1, 1


6. The Game


  1. Select Game
  2. Choose Level 1 to start
  3. Each level has five equations for you to balance. When you think you have balanced the equation correctly, click the "Check" button" in the bottom center of the screen. You will be awarded points if you get the equation correct. You only get two attempts per equation.
  4. Continue on to complete both Levels 2 and 3.
  5. After you complete each level, enter your score in the appropriate question box for that level below.

 

 


Question 6.1

1. Enter your score for Level 1 in the box below by taking a screenshot and uploading it as a file into the answer box.

 

Screenshot Instructions

laptop: Use the snipping tool to highlight an area on the screen that can then be saved to your Google Drive.

Macbook: Command + shift + 4 then highlight the area on the screen that can be saved to your Google Drive.

Chromebook: Ctrl + switch key (button that allows you to switch between windows on top row) will allow you to save your screenshot in your Google Drive.

Upload files that are less than 5MB in size.
File Delete
Upload files to the space allocated by your teacher.


Question 6.2

2. Enter your score for Level 2 in the box below by taking a screenshot and uploading it as a file into the answer box. Use the same instructions provided in question 1 above.

Upload files that are less than 5MB in size.
File Delete
Upload files to the space allocated by your teacher.


Question 6.3

3. Enter your score for Level 3 in the box below by taking a screenshot and uploading it as a file into the answer box. Again, use the same instructions provided in question 1 above.

Upload files that are less than 5MB in size.
File Delete
Upload files to the space allocated by your teacher.