Topic: Balancing Chemical Equations
Date: 3/15/12
NSES: Chemical Reactions- Chemical reactions occur all around us, for example in health care, cooking, cosmetics, and automobiles.
Grade level: 11
SOL: CH3b. balancing chemical equations
Subject: Chemistry
Daily Question: Why should I care about conservation of mass?
Procedures for Learning Experience
Guiding Questions
Engagement: Bill Bryson “A Short History
of Nearly Everything” reading (pg. 134
paragraphs 2-4) about conservation of massRead aloud to students and discuss
implications of reading
Have you ever thought
about where your atoms
came from? Did you ever
think about how long
atoms live? How do you
feel about sharing your
atoms with historical
figures? In this way, could
you say we are all related?
Could you say we are
scientifically reincarnated?
Did you get the same
answer as the person sitting
next to you? Did you check
your atom inventory?
Explanation: ask students to put everything
away and only have whiteboard and marker.
No note-taking! Discussion of conservation
of mass and what that really means followed
by giving students rules for balancing
equations (PowerPoint attached). Then give
students equations to practice balancing with.
Student should use individual whiteboards to
practice.
After 4 or 5 examples, students will be given
a WS to practice balancing with.
Materials
Needed
book
Evaluation
(Assessment)
participation
Approximate
Time Needed
15
Individual
whiteboards,
markers,
PowerPoint,
Interwrite
tablet
Whiteboards, WS
30
30
Extension: for last 15 minutes of class,
students should get into groups of 4 and a
balancing contest will occur. Very difficult
balancing equation problems will be put on
the board and each group will try to balance
them. Every time they think they have one
balanced, I will come and check it with my
key. If they are right, each group member
gets a piece of candy; if they are wrong I will
not tell them what they did wrong.
N/A
Whiteboards,
markers,
candy
Participation,
responses
15
Notes:
Lecture Plan:
Tell students to put all of their pencils and paper away; for the first part I only want them listening and answering my questions. Ask
the students what conservation of mass means to them. What definition would they give for the term? Eventually we should get to the
idea that mass is neither created nor destroyed. Emphasize to the students that this means that atoms aren’t going anywhere and neither
is the mass that they make up; therefore we show that in chemical equations by balancing them. Draw a picture of a balanced equation
to demonstrate that neither atoms nor mass is lost (this is very simple with the Interwrite tablet but here is an example.
2 H2O  2 H2 + O2
V
+
Now that they understand the concept behind balancing, demonstrate how to balance equations in 4 easy steps (look at PowerPoint
slides to help guide). Step 1: Get an unbalanced equation. Step 2: draw boxes around all of the chemical formulas and never change
what is inside the box. Step 3: make an element inventory for each side of the equation (hint- it’s often helpful to have the inventories
in the same order for easy checking). Step 4: write numbers in front of each box (coefficients) until the inventory for each element is
the same before and after the reaction. Voila! Now just hearing the steps is often confusing for students so walk them through an
example. If they are feeling ready, they can work through it with you on their whiteboards, or they can simply watch. Demonstrate
drawing boxes around each chemical formula and stress the importance of this. Students often try to change the formula or put
coefficients in the middle of formulas to balance, but this is not correct. Remind the students that that would be like saying you wanted
to add an extra oxygen atom to water or that you could have half of a molecule. Once the students understand the process, have them
try examples on their whiteboards. Put an equation on the screen and give them several minutes to work through them. Walk around
the room and check on their progress, helping students that seem lost and praising those that are excelling. Ask that students check
their answers with the person next to them and determine where the discrepancies occurred if they do not match. After several
minutes, work through the problem on the screen so that they are having the process modeled for them several times. Have them work
through 3 or 4 examples until they feel ready to work on their own. As you see them becoming more comfortable, ask students to lead
you through the process on the board to make sure they understand it. For tougher problems: a big hint that helps with more difficult
equations is to focus on the elements that only appear once on each side first, then move onto the ones that appear multiple times
(usually hydrogen or oxygen). Most students who struggle with balancing have trouble because they try to look at the whole equation
instead of focusing on one element at a time. Be sure to emphasize: ONE ELEMENT AT A TIME!!!!