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? (video)
General Equation: ________________________________
When two or more reactants combine to form a single product
A + B  AB

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

9. IV. Types of Reactions – Single Replacement
A. What is it? (video)
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

10. IV. Types of Reactions – Single Replacement
See Table _____ to verify if reaction will occur
Example: NaCl + Li 
NaCl + Mg 
NaCl + F2 
NaF + Cl2  J
The element by itself must be above (more active) in order for the reaction to occur
below it
LiCl + Na
No reaction
NaF + Cl2 (NOT BALANCED)
No reaction

11. IV. Types of Reactions – Single Replacement (SKIP)
C. 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

12. V. Types of Reactions – Double Replacement
A. What is it? (video)
Involves an exchange of positive ions between two reacting ionic compounds
B. General Equation:
VIDEO DEMOSTRATION
AX + BY  BX + AY

13. 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)

14. VI. Types of Reactions – Combustion
A. What is it? (video)
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

15. VI. Types of Reactions – Combustion
Balance the following reactions:
HINT FOR BALANCING COMBUSTION REACTIONS: 1. Balance C
2. Balance H
3. Count total number of O on the product (using the added coefficients) and add a coefficient in front of O2 to balance out the O.
___ CH ____ O2  ____ H2O + ______ CO2 1 2 2 1
Elements C H O

16. VI. Types of Reactions – Combustion
Balancing:
_____ C2H4 + _____ O2  ______ H2O + _______ CO2 1 2 3 2

17. Unit 5: Stoichiometry and Chemical Reactions

18. I. What is a mole? 6.02 x 10 23 6.02 x 10 23 atoms of carbon
A mole (mol) represents a certain amount. Just like a dozen bagels represent 12 bagels.
1 mole = ________________________ particles (Avogadro’s Number)
A particle can mean molecule, an atom, an ionic compound.
12 amu = 1 carbon atom
12 g of carbon = 1 mole of carbon atoms = __________________________
6.02 x 10 23
6.02 x atoms of carbon

19. II. Gram Formula Mass 1 mole Cl =
Gram Atomic Mass (GAM) – mass of 1 mole of atoms in an element
Example: Cl:
Subscripts – represent the number of moles of each atom
Examples:
Al2O3 – _______ moles of Al ions, ______ moles of O ions
Ca(NO3)2 - ______ mole of Ca ions, ______ moles of N atoms, ______ moles of O atoms
1 mole Cl =
35 g of Cl (round to the nearest whole number) 2 3 1 2 6

20. II. Gram Formula Mass Mass of 1 mole of a compound
Gram Formula Mass (GFM) –
To find the GFM you add the masses of all of the elements in the compound or molecule.
Examples:
H2O Al2(SO4)3
2. K2CO Zn3(PO4)2 • 4H2O
Mass of 1 mole of a compound
2 (1g) + 1 (16g) = 18 g
2 (27g) + 3 (32g) + 12(16 g) = 342 g
2 (39 g) + 1 (12 g) + 3(16 g) = 138 g
3 (65g) + 2 (31g) + 8(16 g) + 8 (1g) + 4 (16 g) = 457 g

21. VIII. Percent Composition
Think about this: How would you find the percent of boys in our class?
# of boys (part)____ x 100%
Total # of students (whole)

22. VIII. Percent Composition
Equation: (See Ref Tabs) Table ________
Example 1: A g sample contains 3.83 g of iron and g of bromine. What is the percent composition of bromine?
Represents the composition as a percentage of each element compared with the total mass of the compound T
% Composition = mass of part * 100
by mass mass of whole
% Composition = mass of part * = g Br____ x 100 = %
by mass mass of whole g Sample

23. VIII. Percent Composition
Example 2: Find the percent by mass of nitrogen in NH4NO3.
Step 1: Find the GFM: 2 (14 g) + 4 (1 g) + 3 (16 g) = 80 g
Step 2: % Composition = mass of part * = 28 g N x 100 = 35 %
by mass mass of whole g