1. UNIT 4 - REACTIONS
BALANCING EQUATIONS

2. WARM UP 7 minutes In a chemical reaction, what is meant by the terms
“product”
“reactant”?
What type of reaction is this:
CaSO4 + Mg(OH)2 --> Ca(OH)2 + MgSO4
Is the following reaction possible? Why or why not? Na + BaCl2  Ba + NaCl
What are the products of the equation, Na2S + K 
Chromium is characterized by a very high melting point. Use the PToE to identify which of these elements most likely has a similar melting point.
Chlorine C. Bromine
Manganese D. Krypton

3. AGENDA ESSENTIAL QUESTION: Warm Up Announcements Counting Atoms
How do substances interact with each other to produce new ones?
Warm Up
Announcements
Counting Atoms
Balancing Equations
Exit Quiz

4. ANNOUNCEMENTS
Tutoring after school tomorrow. Sign up on website or DON’T SHOW UP.
By Next Thursday , you should have completed and turned in ALL missing assignments.
Upcoming Events: MIDTERMS!!!
Will have everything up to the end of this Unit (Reactions).
Upcoming Events: Unit 4 Test!!!
Types of Reactions
Predicting Products (Single and Double Replacement)
Balancing Equations

5. Unit 4 – subtopic 2: BALANCING EQUATIONS
The Law of Conservation of Mass
Counting Atoms
Balancing Equations

6. THE LAW OF CONSERVATION OF MASS

7. What’s up with the apples?

8. What about these apples?

9. Chemical Reactions  Br Br Br Br Li Li Li Li

10. For the rest of today, we will be balancing chemical equations.
This will seem like a bunch of rules a chemist made up unless you understand the following concepts.

11. Chemical Reaction Notes
1. Law of Conservation of Mass Mass is neither created nor destroyed – it is simply converted from one form to another. 2. Chemical reactions MUST BE BALANCED The number of atoms on the reactant side and the product side must be EQUAL
But how do we count the number of atoms?

12. COUNTING ATOMS There are three rules for counting atoms:
Subscripts apply to the element immediately before it.
Coefficients multiply the entire molecule.
If there are parentheses, the subscript multiplies everything inside the parentheses.

13. Counting Atoms Rules
1. Subscripts apply to the element immediately before it Ex) MgCl2 #Mg ____ #Cl_____ 2. Coefficients multiply the entire molecule Ex) 2C2H6 #C___ #H____

14. 3. If there are parentheses, the subscript multiplies everything inside the parentheses
Ex) 3Be(NO3)2 #Be___
#N____
#O____

15. Counting Atoms 3P6(BrO3)3 1. H2SO4 2. Ca(OH)2 3. NaCl 4. (NH3)3PO4
Example:
Your turn:
How many atoms of each element are in the following molecules?
1. H2SO4
2. Ca(OH)2
3. NaCl
4. (NH3)3PO4
5. 3H2O
3P6(BrO3)3

16. BALANCING EQUATIONS

17. To decide if an equation is balanced:
Compare the number of atoms of each element that appear on each side of the equation.
If the number of atoms is equal then the equation is balanced, if not equal than the equation is not balanced
Ex) N2 + 3 H2  2 NH3
Is it balanced?

18. You Try!
C3H8 + 5 O2  3 CO2 + 4 H2O
Is it balanced?

19. Ok, cool.
BUT HOW DO WE ACTUALLY BALANCE THESE BAD BOYS????!!!

20. When balancing… Draw a line between products and reactants
Tally up atoms of each element on each side
Change coefficients to start balancing (never change subscripts!)
Recalibrate each time you change a coefficient
CHECK YOUR WORK!

21. Balancing Chemical Reactions
Ex 1: ____N2 + ____H2  ___NH3

22. Balancing Chemical Reactions
Ex 2: ____FeO  ____Fe ____O2

23. The best way to learn this is to practice.
With a partner, balance the following equations:
____NO + ____O2  ___NO2
____H2 + ____Cl2  ___HCl
____Fe + ____Cl2  ___FeCl3
4. ____CH4 + ____O2  ___CO2 + ___H2O

24. Partner Practice
1. ____NO + ____O2  ___NO2

25. Partner Practice
2. ____H2 + ____Cl2  ___HCl

26. Partner Practice
3. ____Fe + ____Cl2  ___FeCl3

27. Partner Practice
4. ____CH4 + ____O2  ___CO2 + ___H2O

28. Partner Practice 5. ____ K + ____ Cl2  ____ KCl
6. ____ N2 + ____ F2  ____ NF3

29. Independent Practice For the rest of class
Go to the class website and copy notes (in blue).
Unit 4: Reactions
Balancing Equations
Work on and complete Worksheet 4.2.
Show your work in balancing equations on the back of the worksheet.
When you get done: come and see me. If you are done, I will have you check your answers against my answer key. If you get any wrong, you must go back and fix them.
If you get done with that: You may help a neighbor.

30. Exit Ticket Balance the following equations: ___Na + ___Cl2  ___NaCl
___Al + ___HBr  ___AlBr3 + ___H2