1. Unit 5: Stoichiometry and Chemical Reactions

2. I. Parts of a Chemical Reaction and Balancing
What is a chemical reaction?
Example: (video)
HCl (aq) + Zn (s)  H2(g) + ZnCl2(aq) (NOT BALANCED)
One or more substances are made into NEW substance(s) (bonds are broken and/or made)
Reactants
yields
Products
Physical state of substances

3. I. Parts of a Chemical Reaction and Balancing
Example: HCl (aq) + Zn (s)  H2(g) + ZnCl2(aq) (NOT BALANCED)
 Problem:
The above chemical reaction breaks the Law of Conservation of Mass:
Matter is neither created or destroyed in a chemical reaction
So… the numbers of atoms must remain unchanged in a reaction

4. I. Parts of a Chemical Reaction and Balancing
Balancing Equations: Coefficients are used to balance the number of at atoms of each element on both sides of the reaction. Coefficients must be the smallest whole number that balance the reaction.
NOTE: Coefficients can be changed, HOWEVER, subscripts CANNOT!
Example: ____ HCl (aq) + ____ Zn (s)  ____ H2(g) + ____ ZnCl2(aq) 2 1 1 1
Reactants
Elements
Products H Cl Zn

5. I. Parts of a Chemical Reaction and Balancing
Examples: Balance the following chemical reactions
_____ N2 + _____ H2  _____ NH3
2. _____ Al2O3  _____ Al + ____ O2
Complete 3 and 4 on your own.
Elements 1 3 2
Elements 2 4 3

6. I. Parts of a Chemical Reaction and Balancing
Examples: Balance the following chemical reactions
3. _____ Al + _____ Br2  _____ AlBr3
4. _____ AlBr3 + ___ Cl2 _____ Al Cl3+ ____ Br2
Elements 2 3 2 2
Elements 2 3 3

7. II. Types of Reactions - Synthesis
What is it?
General Equation: ________________________________
When two or more reactants combine to form a single product
A + B  AB

8. Checks for Understanding
Real World Example: (video)
Magnesium ribbon is heated and reacts with oxygen in the air forming magnesium oxide
After watching the demonstration, what are some observations you made that proved that a chemical reaction occurred?
Balance the following chemical reaction
____ Mg (s) + ____ O2 (g)  ____ MgO (s)  2 1 2
Elements

9. II. Types of Reactions - Synthesis
C. Balancing: Balance the following synthesis reactions:
1. ____ S + ____ O2  ____ SO3
____ C + ____ H2  ____ C3H8
Complete 3 and 4 on your own and
then check with your partner
Elements 2 3 2 3 4 1
Elements

10. II. Types of Reactions - Synthesis
D. Chemical Reactions in Words:
Write and balance the following equations. Remember to criss-cross and pay attention to diatomic elements (7 - H club).
Iron and oxygen yields iron (III) oxide 4 3 2
___ Fe
+ ___ O2
 ___ Fe2O3

11. II. Types of Reactions - Synthesis
Checks for Understanding 3. Practice: Write a balanced chemical reaction for each reaction described below Sulfur and oxygen Chromium and oxygen yields sulfur trioxide yields chromium (III) oxide 2 3
___ S
+ ___ O2 4 3
___ Cr
+ ___ O2 2
 ___ SO3 2
 ___ Cr2O3

12. III. Types of Reactions - Decomposition
What is it?
General Equation: ________________________________
Single compound is broken down (decomposed) into two or more simpler substances
AB  A + B

13. Checks for Understanding
Real World Example: (video)
Hydrogen peroxide decomposes into water and oxygen
After watching the demonstration, what are some observations you made that proved that a chemical reaction occurred?
Balance the following chemical reaction
____ H2O2 (l)  ____ H2O (l) + ______ O2 (g) 2 2 1
Elements

14. III. Types of Reactions - Decomposition
C. Balancing: Balance the following synthesis reactions:
1. ____ HgO  ____ Hg + ____ O2
____ AgCl  ____ Ag + ____ Cl2
Complete 3 and 4 on your own and
then check with your partner
Elements 2 2 1 2 2 1
Elements

15. III. Types of Reactions - Decomposition
D. Chemical Reactions in Words:
Write and balance the following equations. Remember to criss-cross and pay attention to diatomic elements (7 - H club).
Nitrogen Triiodine decomposes to nitrogen and iodine 1 3
___ NI3 2
 ___ N2
+ ___ I2

16. Checks for Understanding
3. Practice: Write a balanced chemical reaction for each reaction described below Magnesium chloride decomposes Aluminum oxide decomposes into magnesium and chlorine into aluminum and oxygen
___ MgCl2 1
___ Al2Cl3 2 1 1
 ___ Mg
+ ___ CI2 4 3
 ___ Al
+ ___ CI2

17. IV. Types of Reactions – Single Replacement
A. What is it?
B. General Equation:
2K (s) + 2H(OH) (l)  H2 (g) + 2KOH (aq)
Atoms of one element replace the atoms of a second element in a compound (metal switches with metal or nonmetal switches with nonmetal)
Always involves an element and a compound
Reaction will only occur if the single element is more reactive than the element in the compound (see Table J)
A + BX  B + AX

18. IV. Types of Reactions – Single Replacement
See Table _____ to verify if reaction will occur
***A metal/nonmetal will replace any metal/nonmetal listed _________
Example: NaCl + Li 
NaCl + Mg 
NaCl + F2 
NaF + Cl2  J
The element by itself must be above (more reactive) in order for the reaction to occur
below it
LiCl + Na
No reaction
NaF + Cl2 (NOT BALANCED)
No reaction

19. IV. Types of Reactions – Single Replacement
C. Balancing: Balance the following synthesis reactions:
1. ____ Cl2 + ____ KBr  ____ KCl + ____ Br2
___ Fe + ____ AgC2H3O2  ___ Fe(C2H3O2)3 + ____ Ag
____ Li + _____ H(OH)  ___ LiOH + ___ H2 2 1 1 2
Elements K Cl Br 1 3 3 1 2 2 2 1

20. IV. Types of Reactions – Single Replacement
D. Finish the Chemical Reaction:
Use Table J to see if the following reactions can occur. If it can, write the product and balance the equation (if necessary). Remember to criss-cross and pay attention to diatomic elements (7 - H club).
____ Zn + ____ H2SO4  ___________________________
____Pb + _____ FeCl3  ___________________________
____ Cl2 + _____ LiI  ____________________________ 1 1 1
___ ZnSO4 +___ H2 1
No reaction (Pb is BELOW Fe) 2 2 1
___ LiCl + ______ I2 1

21. IV. Types of Reactions – Single Replacement
D. Chemical Reactions in Words: Write and balance the following equations. Use Table J to see if the following reactions can occur. If it can, write the product and balance the equation (if necessary). Remember to criss-cross and pay attention to diatomic elements (7 - H club).
1. Calcium reacts with Sodium chloride
Potassium reacts with magnesium fluoride
3. Magnesium reacts with zinc nitrate 1 2
___ Ca +___ NaCl  2
___ CaCl2 +___ Na 1 2
___ K +___ MgF2  2 1
___ Mg+___ KF 1 1 1 1 1
___ Mg+___ Zn(NO3)2 
___ Mg(NO3)2 +___ Zn

22. V. Types of Reactions – Double Replacement
A. What is it?
Occurs only if a solid, gas, or water is formed
Precipitates:
See Table ____: Examples – Cu(NO3) _____ Ca3(PO4)2 ____
PbCl2 ______ Ba(OH)2 ____
Involves an exchange of positive ions between two reacting ionic compounds
A solid formed as a product of a reaction that does not dissolve in water (insoluble) F
(aq)
(s)
(s)
(aq)

23. V. Types of Reactions – Double Replacement
B. General Equation:
VIDEO DEMOSTRATION
AX + BY  BX + AY

24. V. Types of Reactions – Double Replacement
C. Balancing: Balance the following reactions
____ BaCl2 (aq) + ____ H2SO4 (aq)  ____ BaSO4 ( ) + _____ HCl ( )
____ Al(NO3)3 (aq) + ___ NaOH (aq)  ____ Al(OH)3 ( )+ _____ NaNO3 ( )
____ Ca(OH)2 ( ) + ____ H2SO4 ( )  ____ HOH ( ) + ____ CaSO4 2 1 1 s aq 1
Elements Ba Cl H
SO4 1 3 1 3 s aq 1 1 2 1 aq aq l
(s)

25. V. Types of Reactions – Double Replacement
D. Finish the Chemical Reaction: Balance the following reactions
Write the products and balance the equation (if necessary). Remember to criss-cross.
____ Na2S (aq) + _____ Cd(NO3)2 (aq)  _______________________________
____BaCl2 (aq) + ____ H2SO4 (aq)  _______________________________________
____ BaCl2 (aq) + _____ K2CO3 (aq) _________________________________ 2 1 1 1
___ NaNO3 (aq) +___ CdS (s) 1 1 1 2
___ BaSO4 (s) +___ HCl (aq) 1 2 1 1
___ BaCO3 (s) +___ KCl (aq)

26. V. Types of Reactions – Double Replacement
Chemical Reactions in Words:
1. Calcium Nitrate + Sodium Carbonate
2. Aluminum nitrate and sodium hydroxide 1 1
___ Ca(NO3)2 (aq) +___ Na2CO3 (aq) 2
___ CoCO3 (s) +___ NaNO3 (aq) 1 1 3
___ Al(NO3)3 (aq) +___ NaOH (aq)  3
___ Na(NO3) (aq)+___ Al(OH)3 (S) 1

27. VI. Types of Reactions – Combustion
A. What is it?
General Equation (VIDEO – Combustion of Methane (g)):
An organic compound (consists of C and H) reacts with oxygen and creates ONLY carbon dioxide (CO2) and water (H2O)
Organic Compound + O2  H2O + CO2

28. VI. Types of Reactions – Combustion
Balancing:
Balance the following reactions:
____ C4H12 + ____ O2  ____ H2O + ______ CO2
TRICKY!!!
____ CH3OH + ____ O2  ____ H2O + _____ CO2
_____ C2H6 + _____ O2  ______ H2O + _______ CO2 1 7 6 4
Elements C H O 3 4 2 2 2 5 6 4