1. Bell work:
[How long did you study for the last test OUTSIDE of class?] As usual, please be honest.

2. Balancing Chemical Equations
Demos to start

3. The Law of Conservation of Matter
Matter cannot be created nor destroyed
So Atoms cannot simply appear or disappear.
However many atoms of each element you begin with before a chemical reaction- that same number of atoms will still be there after a chemical reaction.

4. The Law of Conservation of Matter Cont.
But if no atoms are created how can a chemical change take place?
The same number of atoms will be there- but they will be put together in different ways! Kind of like Legos…
To be sure the number of atoms remains the same before and after a reaction, you must learn the skill of…

5. Balancing Chemical equations!
You will start with a chemical reaction like this one…
Mg + O MgO
The arrow means “changes to” or “produces”
Reactants (what you start with)
Products (what is made)

6. Balancing Chemical equations!
Is the equation already balanced? See if there are equal numbers of each elements on both sides.
Mg + O MgO
1 magnesium on this side
Also 1 magnesium on this side
only 1 oxygen on this side- so the equation is not balanced.
2 oxygens on this side

7. Balancing Chemical equations!
Balance the equations by putting coefficients (large numbers) IN FRONT of the entire compound.
Mg + O MgO 2 2
Now there are now 2 Mg and 2 oxygens on this side.
But now this side needs 2 Mg to balance the equation. Put a coefficient of 2 in front of Mg.

8. Balancing Chemical equations!
Now check to see if both sides have equal numbers of elements.
Mg + O MgO 2 2
This side also has 2 Mg.
This side has 2 Mg.
This side has 2 O also.
This side has 2 O.
Now this chemical equation is BALANCED.
Think about the law of conservation of matter…Why is balancing important?

9. Answer:
A balanced reaction proves that no matter (atoms) have been created or destroyed!

10. Counting Atoms Mg = 1 atom of magnesium O2 = 2 atoms of oxygen
MgCl2
Cl= 2 atoms of chlorine
H= 2
H2SO4
S= 1
O= 4

11. Counting Atoms N= 1 H= 4 NH4Cl Cl= 1 Mg= 1 Mg(NO3)2 N= 2 O= 6
(NH4)3PO4
N= 3
P= 1
H= 12
O= 4

12. Counting Atoms Ti= 1 Cr= 2 Ti(CrO4)2 O= 8 Ca= 3 Ca3(PO4)2 P= 2 O= 8
(NH4)2CO3
N= 2
C= 1
H= 8
O= 3

13. Counting Atoms 2 Mg atoms 2Mg= 3O2= 6 atoms of oxygen Mg= 3 Mg 3MgCl2
Cl= 6 Cl
H= 6
3H2SO4
S= 3
O= 12

14. Counting Atoms N= 4 4NH4Cl H= 16 Cl= 4 Mg= 6 6Mg(NO3)2 N= 12 O= 36
3(NH4)3PO4
P= 3
N= 9
H= 36
O= 12

15. Bell work: date: Balance these medium-hard problems.
NH3 + O HNO3 + H20
ZnS + O ZnO + SO2
PH3 + O P2O H2O
HBr + H2SO H2O + SO2 + Br2

16. A review:Counting Atoms
H= 4
4NH4Cl
NH4Cl
H= 16
Cl= 1
Cl= 4
Mg= 1
Mg(NO3)2
Mg= 6
6Mg(NO3)2
N= 2
N= 12
O= 6
O= 36
N= 3
(NH4)3PO4
N= 9
3(NH4)3PO4
H= 12
H= 36
P= 1
P= 3
O= 4
O= 12

17. A review:Counting Atoms
H= 4
4NH4Cl
NH4Cl
H= 16
Cl= 1
Cl= 4
Mg= 1
Mg(NO3)2
Mg= 6
6Mg(NO3)2
N= 2
N= 12
O= 6
O= 36
N= 3
(NH4)3PO4
N= 9
3(NH4)3PO4
H= 12
H= 36
P= 1
P= 3
O= 4
O= 12

18. Bell work: date: 2) ZnS + O2 ZnO + SO2 3) PH3 + O2 P2O5 + H2O
Balance these medium-hard problems.
1) NH O HNO H20
2) ZnS + O ZnO SO2
3) PH O P2O H2O
4) HBr + H2SO H2O + SO2 + Br2 2 2 3 2 2 2 4 3 2 2

19. Bell work: date: 2) SiO2 + HF SiF4 + H2O 3) CuO + NH3 Cu + N2 + H2O
Warm up !Balance these problems.
1) Al + HCl AlCl3 + H2
2) SiO2 + HF SiF H2O
3) CuO + NH Cu + N2 + H2O
4) HNO H2O + NO2 + O2

20. Balancing Mini 1) CaF2 + H2SO4 CaSO4 + HF 2) KClO3 KCl + O2
3) P2O H2O H3PO4
4) H2S O H2O SO2
5) N2S O N2O SO2
6) C2H6O O CO H2O 2 2 2 3 3 2 2 2 3 2 2 2 9 2 6 3 2 6 3 2 4 2 3 6 2

21. Balancing lab activity
1) CH O CO H2O 2 2
Use a pencil or pen for the arrow H O H O O C H + 1 + C O H O 1 H H H O O 2 2 H O
2 H2O are now showing
2 O2 are now showing

22. Bell work: date: 2) TiO + NH3 Ti + N2 + H2O 3) SO2 + HCl SCl4 + H2O
BWarm up II !Balance these problems.
1) Ga + HBr GaBr H2
2) TiO + NH Ti + N2 + H2O
3) SO2 + HCl SCl H2O
4) HNO H2O + NO2 + O2
5) MgS + O MgO SO2
6) P2O H2O H3PO4
7) Al H2SO Al2(SO4) H2 2 2 6 2 3 3 2 3 3 4 2 4 4 2 3 2 2 3 2 2 3 3

23. Bell work: date: 2) AgNO3+ MgCl2 AgCl+ Mg(NO3)2
BWarm up III !Balance these problems.
1) N2 + H NH3
2) AgNO3+ MgCl AgCl+ Mg(NO3)2
3) BaSe + O BaO SeO2
4) Mg3N H2O Mg(OH)2 + NH3 2 3 2 2 2 3 2 2 6 3 3