1. Stoichiometry

2. What is stoichiometry?
The study of quantitative relationships in a balanced chemical equation
Equations represent chemical reactions

3. Physical vs. Chemical Change
Physical Change =
Chemical Change =
Change in form/appearance
Examples:
Dissolving & phase changes
Change in identity
Change in formula representing
a substance

4. Evidence of a Chemical Reaction
Temperature change
Emission of Light Energy
Change in identifying property:
Color, mp, bp, density, Hf, Hv, c …
Formation of Gas
Bubbling, odor
Formation of Solid
Precipitation

5. Chemical Equations A + B  C + D
Left Side = Reactants (starting materials)
Right Side = Products (ending materials)
“” is read as produces/yields
How do we show the physical state of the reactants & products?
(s), (l), (g), (aq)

6. Law of Conservation of Matter
Matter is neither created nor destroyed
in a chemical reaction
Mass reactants = Mass products
Chemical bonds in reactants may break
New bonds may form to produce products
Number of atoms of each element is “constant”
# of atoms of each element is the same on both sides of the equation

7. Coefficients in Chemical Equations
Numbers in front of formulas called coefficients
apply to everything following in formula
Connect microscopic world with macroscopic world
Microscopic: Coefficients represent numbers of individual atoms or molecules
Macroscopic: Coefficients give mole ratios!
Moles  connected to mass (MOLE MAP!)

8. Writing Chemical Equations
Begin with word equation
describes what happens
Next go to skeleton equation
replace names of substances with chemical formulas
Balance skeleton equation
balanced equation must demonstrate law of conservation of mass

9. Equation Balancing Survey skeleton equation (left to right)
Count up # of each type of atom on reactant side
Count up # of each type of atom on product side
Use COEFFICIENTS to balance the numbers of each type of atom
Make successive passes checking ONE ELEMENT AT A TIME
NEVER CHANGE SUBSCRIPTS IN FORMULAS
would change identity of reactant/product

10. Balanced Equations Coefficients must be in lowest possible ratios
Double check your work
Do one last pass to check that all # are same on both sides
Use table to keep track of # each element

11. Example 1 Fe + O2  Fe2O3 Left Side: 1 Fe and 2 O
Right Side: 2 Fe and 3 O
Hint: LCM of 2 and 3 = 6 Get O to 6
Fe O2  2 Fe2O3
O’s are balanced - Now balance Fe
4 Fe + 3 O2  2 Fe2O3
4 Fe and 6 O each side

12. Example 2
Na + H2O  NaOH + H2
Notice: even # H’s on left, odd # on right
Have to make # H’s on right even
Put a 2 in front of NaOH
Na + H2O  2 NaOH + H2
Put a 2 in front of Na to balance Na’s
2 Na + H2O  2 NaOH + H2
2 in front of H2O to balance O and H
2 Na H2O  2 NaOH + H2

13. Example 3 AgNO3 + MgCl2  Mg(NO3)2 + AgCl
Hint: Treat NO3-1 as one unit since appears on both sides of equation
Balance NO3-1 on the left with a 2
2 AgNO3 + MgCl2  Mg(NO3)2 + AgCl
Balance Ag’s and Cl with a 2
2 AgNO3 + MgCl2  Mg(NO3) AgCl

14. Chemical Reactions

15. Types of Reactions Synthesis Decomposition Single Replacement
Double Replacement
Combustion

16. Synthesis Format: A + B  C Identifying feature: 1 product only
Note: A and B may be elements or compounds,
C is a compound
Ex: 2 Fe(s) Cl2(g)  2 FeCl3(s)
2 Na(s) + Cl2(g)  2 NaCl(s)
CaO(s) + H2O(l)  Ca(OH)2(s)

17. Decomposition Format: AB  A + B Identifying feature: 1 reactant only
Note: A & B may be elements or compounds
Ex: NaN3(s)  2 Na(s) N2(g)
NH4NO3(s)  N2O(g) H2O(g)

18. Single Replacement Format: A + BX  AX + B Identifying Feature:
Element + Compound 
Different Element + Different Compound
Ex: 2 Li(s) H2O(l)  2 LiOH(aq) + H2(g)
Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq)

19. Double Replacement Format: AX + BY  AY + BX Identifying feature:
2 compounds yield 2 new compounds
Ex:
Ca(OH)2(aq) + 2HCl(aq)  CaCl2(aq) +
2 H2O(l)
2 NaOH(aq) + CuCl2(aq)  2 NaCl(aq) +
Cu(OH)2(s)

20. Combustion or Reaction with O2
Format: A + O2  B ( + C + …)
Identifying feature: One of reactants is O2
Note: A can be an element or a compound,
usually more than 1 product
Ex:
CH4(g) O2(g)  CO2(g) H2O(g)
For Regents synthesis tops combustion:
2 H2(g) + O2(g)  2 H2O(g)
C(s) + O2(g)  CO2(g)

21. Identify the Reaction Type
CaO + CO2  CaCO3
2 H2O  2 H2 + O2
NaOH + HCl  NaCl + H2O
Zn HCl  ZnCl2 + H2
2 Mg + O2  2 MgO
Mg + H2SO4  MgSO4 + H2
2 KClO3  2 KCl O2
AgNO3 + NaCl  NaNO3 + AgCl
Synthesis
Decomposition DR SR
Synthesis SR
Decomposition DR

22. Stoichiometry!!!
Use balanced chemical equations to predict amount of given reactant or product under certain conditions
Remember: DON’T mess with the subscripts !!