General Principle
to understand that matter can neither be destroyed nor created
to identify combination and combustion reactions
to describe and write chemical reactions with words, symbols, and drawings
to balance chemical reactions

Anticipatory Set
Display on a transparency the recipe for making chocolate chip cookies in three forms- paragraph, equation form (3/4 c. sugar + . . . + 2 c. chocolate chips+heat= 12 cookies), and pictorial form.
Have students convert the recipe to making 24 cookies instead of 12
Have students share what form was the easiest to use for conversion
Discuss other ways in which the different forms compare

Statement of Objective
You will be able to balance two kinds of chemical reactions: combustion and combination, enabling you to use the equation to derive a recipe. You will be able to write these recipes in three different forms: words, symbols, and drawings. Balancing equations is important whenever you are synthesizing compounds in chemistry.

Instructional Input
Show combustion of ammonium dichromate. Demonstrate that although the solid seems to be disappearing, a gas is forming- thus conversion and conservation of matter.
Relate the combustion to a balanced reaction written out in all three forms. Point out characteristics that make it a combustion reaction.
Show combination of hydrochloric acid and sodium bicarbonate. Demonstrate that again, gas forms.
Relate the combination reaction seen to a balanced reaction written out in all three forms. Point out characteristics that make it a combination reaction.

Modeling
Show what to do if the reaction is not already balanced. Have transparency with empty chart organizing the steps of balancing the reaction. Fill in blanks using a new reaction. Go through each step of the thought process ("think out loud").

Check for Understanding
Hand out to each student the same chart used in the modeling section.
Have the students pair up. Give problem A to one student and problem B to the other.
After they have completed the problem, have them switch charts and check each other's work.
Walk around the room to "check for understanding". Repeat modeling if necessary.

Guided Practice
Hand out a worksheet that varies the form the reaction.
Have them complete on their own the identification and the balancing of the reaction. Continue to monitor for students who are struggling. Allow the pairs of students to ask each other for help.

Independent Practice
For homework, have them complete a similar worksheet, but have them time how long it takes them to do every five problems. Charting their speed motivates them to put effort into doing these quickly. This ability is important because balancing equations is needed often.

Artful Ending
Bring back the idea of recipe. Ask them how these reactions are a recipe. What information can we glean from them?
Tell them that tomorrow we will use the equations to indicate what and how much reactants to use to synthesize the desired product.
 
 
 

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