1. Unit 8: Reactions And Stoichiometry

2. What is a chemical reaction?
Chemical Reaction: one or more substances are made into one or more NEW substances (bonds are broken and/or formed)
Reactant: a substance that undergoes a change in a chemical rxn(LEFT side)
Product(s): what is formed during chemical rxn (RIGHT side)
Arrow means “yield”

3. Balancing Chemical Equations
**LAW OF CONSERVATION
Mass (matter), charge and energy are always conserved in a chemical rxn
Mass at the beginning = mass at the end
Same kind and number of atoms on each side of the reaction

4. Word equation  formula equation
Solid potassium chlorate is heated in the presence of a manganese (IV) oxide catalyst to form solid potassium chloride and oxygen gas.

5. Balancing Rules Adjust coefficients ONLY!!!
NEVER touch the subscripts.
Report the final answer using the smallest, whole # coefficients.
Tip:
Keep PAIs together as a unit and balance these first!

6. Balancing Practice
(ex) ____Ag + ____AuCl3  ____AgCl + ____Au (ex) ____Pb(NO3)2 +____NaCl ____PbCl2 + ____NaNO3 **(ex) ____CH4 + ____O2  ____CO2 + ____H2O (ex) ____Fe + ____O2  ___Fe2O3

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

8. 1. Synthesis (Combination) Reaction
Two or more reactants combine to form a single product
A + B  AB

9. 2. Decomposition
One reactant breaks apart into two or more simpler substances
AB  A + B

10. 3. Single Replacement
Both the reactant and product side consist of 1 element and 1 compound

11. 4. Double Replacement
Both the reactant and product side have compounds

12. 5. Combustion CH4 + 2O2 CO2 + 2H2O Hydrocarbon + O2  CO2 + H2O
Chemical change in which an element or a compound reacts with oxygen, producing energy
Often, the reactant is a hydrocarbon (contains hydrogen and carbon)
Hydrocarbon + O2  CO2 + H2O
CH O2 CO2 + 2H2O

13. Writing Synthesis Reactions
Magnesium and oxygen 
Aluminum and chlorine 

14. Table J: SR Reactions
More reactive metals replace less reactive metals
K + NaCl  KCl + Na
Na + KCl  NR
More reactive non-metals replace less reactive non-metals
Cl2 + 2 NaI  2 NaCl + I2
I2 + 2NaCl  NR

15. Practice 1) Zn (s) + CaF2 (aq)  2) Mg (s) + Al(NO3)3 (aq)
3) Br2 (l)+ NaI (aq) 
4) Na (s) + Al2(SO4)3 (aq) 
Exit Slip: Ca + HBr 
F2 + KCl 

16. Writing Double Replacement Rxns
Two ionic compounds exchange ions to form 2 new compounds
CuSO4 (aq) + Na2S (aq)  _______ + ________
K2CO3 (aq) + Pb(NO3)2 (aq)  _______ + _______
NaCl (aq) + NH4NO3 (aq)  _______ + _______

17. Double Replacement Demo

18. Practice Using Table F:
Determine if the following are soluble (aq) or insoluble (s):
PbCl2
Mg3(PO4)2
Ba(OH)2
Sr(ClO3)2
Na2CO3

19. Warm-Up
Predict the products of the following single replacement rxn. Write both a word equation and a complete, balanced chemical equation. aluminum + copper (II) chlorate 

20. Stoichiometry
The calculation of quantities in chemical reactions is called stoichiometry

21. Using Mole Ratios
A mole ratio is a conversion factor made from the coefficients of a balanced equation

22. Stoichiometry Problems: Summary
Mole  Mole
Grams  Moles or Moles  Grams
Grams  Grams

23. Mole  Mole 4Fe (s) +O2 (g)  2Fe2O3 (s)
How many moles of iron are required to produce 1 mol of iron (II) oxide?
How many moles of oxygen gas are required to produce 4 mol of iron (II) oxide?
How many grams of iron (II) oxide are produced when 1.29 mol oxygen gas react completely?

24. Gram  Gram
4Fe (s) +O2 (g)  2Fe2O3 (s)
How many grams of iron are required to produce 66.7 grams of Fe2O3?

26. Table I Stoichiometry
Shows the ΔH for various different reactions (combustion, synthesis, dissolving)
ΔH (heat of reaction)
Negative sign indicates heat is released (exo)
Positive sign indicates heat is absorbed (endo)
To find ΔH for the reverse of ANY reaction, switch the sign of ΔH

27. Table I Problems
1) How much heat is released during the combustion of mol C3H8 (g)?
2) How much heat is absorbed when forming 1.20 mol of HI from its elements?
3) How much heat is absorbed when forming 62.3 g NO2 (g) from its elements?

28. Limiting and Excess Reactants (Reagents)
Limiting- the substance used up first
Excess means that substance is NOT used up completely in the rxn

29. Example: Limiting Reactant Problem
If 28 g of Fe react with 24 g of S to produce FeS
What is the limiting reactant?
How many grams of FeS are produced?
How many grams of excess reactant?

30. Percent Yield
Theoretical yield: the maximum amount of product that could be formed from the given amounts of reactants (mass:mass calc.)
Actual yield: the amount of product that actually forms when the rxn is carried out in the lab (measured result)

31. Percent Yield Percent Yield= experimental yield x 100%
theoretical yield