11 17 how are equations balanced
TRANSCRIPT
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Launch: 11/17 Grab your binder and immediately take a seat!
Place homework (practice questions) on desk.
Mg + 2H2O Mg(OH)2 + 2H2
3. Is the above equation balanced? a. No, because the number of H atoms is not equal
b. No, because the number of O atoms is not equal c. Yes, because the number of Mg atoms is not equal
d. Yes, because there are equal numbers of atoms on both sides of the equation
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Launch 11/17 4. Hydrogen gas (H2) and oxygen gas (O2) react to
form water (H2O). Which of these represents a properly balanced equation for this reaction?
a. H2 + O2 H2O
b. 2H2 + 2O2 2H2O
c. 2H2 + O2 2H2O
d. H2 + 2O2 2H2O
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Announcements Unit #5: Chemical Reactions & Stoichiometry
Class points end next week Get your HW done Be respectful
Quiz on Friday!
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How are equations balanced?
Mr. Heffner 11/17/09
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Is the below equation balanced?
Cl2 + H2 2HCl
Review
2 X Cl 2 X H 2 X H 2 X Cl
Multiply the coefficients and
subscripts Yes, it is balanced!
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How are equations balanced? There is a 3-step process for balancing
equations:
1. Count the atoms on both sides
2. Change a coefficient & multiply out
3. Check tally (and repeat)
Only one rule: you can’t change the subscripts
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Example #1 Balance the equation,
H2 + O2 H2O
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Step #1: Count the atoms on both sides
H2 + O2 H2O
Example #1
2 X H 2 X O 2 X H 1 X O
Put it underneath Unbalanced!
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Step #2: Change coefficient & multiply out
H2 + O2 H2O
Example #1
2 X H 2 X O 2 X H 1 X O
2
2X( ) 4 X H 2 X O
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Step #3: Check tally (and repeat)
H2 + O2 H2O
Example #1
2 X H 2 X O
2
4 X H 2 X O
2
4 X H
2X( )
Still unbalanced!
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Step #3: Check tally (and repeat)
H2 + O2 H2O
Example #1
2 X O
2
4 X H 2 X O
2
4 X H
Balanced!
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Activity Make the equation on your whiteboard
Balance the equation with the 3-step method 1. Count the atoms 2. Add a coefficient 3. Check tally (and repeat)
Raise hand to get checked off
Record reactants, products, and final balanced equation on worksheet
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Practice Questions Practice question handouts
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Exit Slip 1. In a balanced equation
a. the reactant atoms are destroyed to make the products
b. the number of atoms on the reactants side of the equation is equal to the number of atoms on the products
c. the number of atoms on the reactants side of the equation is not equal to the number of atoms on the products
d. all compounds have a coefficient of at least 2
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Exit Slip H2 + Cl2 HCl
2. Is the above equation balanced? a. No, because H2 has a coefficient of 2.
b. No, because the number of Cl and H atoms are not equal.
c. Yes, because the number of H atoms is not equal on both sides.
d. Yes, because there are equal numbers of atoms on both sides of the equation.
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Exit Slip 4K + O2 2K2O
3. In the already balanced reaction above, what is the coefficient for O2?
a. 0 b. 1
c. 2 d. 4
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Exit Slip __C + __Br2 __CBr4
4. When the equation above is completely balanced, the coefficient for Br2 would be
a. 0
b. 1
c. 2
d. 4
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Exit Slip __Na + __H2O __NaOH + __H2
5. When the above equation is completely balanced, the coefficient for NaOH would be
a. 1.
b. 2. c. 4.
d. 8.
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Homework Finish practice question worksheet