1. CHEMICAL EQUATIONS AND STOICHIOMETRY
CHAPTER 4:
CHEMICAL EQUATIONS AND STOICHIOMETRY

2. 4.0 OBJECTIVES
Balance simple chemical equations and interpret the meaning of coefficients in the equation.
Understand the meaning of the term stoichiometry and calculate the mass of any species in an equation based on data provided about any other species.
Use stoichiometry to state which reagent is the limiting reagent and to state actual, theoretical and percent yield.
Apply stoichiometry principles to determining the empirical formula of a compound.

3. HOMEWORK #1 - 9, 11, 45, Worksheets in Packet
Balancing Equations
# , 15, 17, 19, 47, 49
Basic Mass Stoichiometry
# , 23, 25
Limiting Reactants
# , 29, 31, 33, 35
% Yield
# , 39, 43, 53, 55
Empirical/Molecular Formulas from Stoich—HARD!!!!
# , 52, 57, 59, 61, 63, 65
Summary Questions: EVERYTHING!

4. 4.1 CHEMICAL EQUATIONS AND 4.2 BALANCING CHEMICAL EQUATIONS
1. Parts of the equation: reactants, products, subscripts, coefficients, yield states of matter
Ex. CaC2 (s) + 2 H2O (l)  C2H2 (g) + Ca(OH)2 (aq)

5. 4.1 CHEMICAL EQUATIONS AND 4.2 BALANCING CHEMICAL EQUATIONS
2. Law of Conservation of Mass
Antoine Lavoisier
“matter can neither be created nor destroyed”
If Completely Converted:
100 g-Reactants = 100 g-Products
5 atoms O-Reactants = 5 atoms O-Products
Balanced Chemical Eqns. demonstrate this!!

6. 4.1 CHEMICAL EQUATIONS AND 4.2 BALANCING CHEMICAL EQUATIONS
3. Coefficients, only
Demonstrate atom to atom or compound to compound relationship
More Likely:
mol to mol relationship between atoms/compounds
Aka “stoichiometry”

7. 4.1 CHEMICAL EQUATIONS AND 4.2 BALANCING CHEMICAL EQUATIONS
4. Elements are written as single atoms, except for diatomic elements and P4 & S8
BrINClHOF -or- HONClBrIF

8. 4.1 CHEMICAL EQUATIONS AND 4.2 BALANCING CHEMICAL EQUATIONS
5. Symbols used in chemical equations:
(s) catalyst
(ℓ) electricity
(g) UV light
(aq) ∆

9. 4.1 CHEMICAL EQUATIONS AND 4.2 BALANCING CHEMICAL EQUATIONS
6. Balancing equations
Number of atoms of each element must be the same on both sides of the equation
The total number atoms of an element is the product of its coefficient and subscript; distribute parenthesis
Sum all atoms of an element even if it occurs in more that one compound on that side
Polyatomic ions can be handled as a cohesive unit if they remain a unit on the product side

10. 4.3 MASS RELATIONSHIPS IN CHEMICAL REACTIONS: STOICHIOMETRY
2H2(g) + O2(g)  2H2O(g): relationships
2 molecules: 1 molecule: 2 molecules
2 moles: 1 mole: 2 moles
2:1:2 ratio is preserved
Always need twice as much hydrogen as oxygen

11. 4.3 MASS RELATIONSHIPS IN CHEMICAL REACTIONS: STOICHIOMETRY
Coefficients can stand for:
**Moles** theoretical yield:
Atoms the amount of product
Molecules that “should” be produced
Formula Units based on the available
amounts of reactants
NOT grams!!

12. 4.3 MASS RELATIONSHIPS IN CHEMICAL REACTIONS: STOICHIOMETRY
Ex4.1 Write and balance the equation for the combustion (rapid oxidation) of benzene, C6H6, to carbon dioxide and water vapor.

13. 4.3 MASS RELATIONSHIPS IN CHEMICAL REACTIONS: STOICHIOMETRY
Ex4.2 How many moles of carbon dioxide are produced in the above reaction when starting with 0.23 moles of benzene and an excess of oxygen?

14. 4.3 MASS RELATIONSHIPS IN CHEMICAL REACTIONS: STOICHIOMETRY
Ex.4.3 How many grams of water are produced, starting with 0.23 moles of benzene and an excess of oxygen?

15. 4.3 MASS RELATIONSHIPS IN CHEMICAL REACTIONS: STOICHIOMETRY
Ex4.4 How many grams of water are produced, starting with 3.00 grams of benzene and excess oxygen?

16. 4.3 MASS RELATIONSHIPS IN CHEMICAL REACTIONS: STOICHIOMETRY
Ex4.5 Write the reaction for the synthesis of antimony fluoride (SbF3) from its elements. How many grams of fluorine are required to react with exactly 1.00 moles of antimony? What is the theoretical yield of product, in grams?

17. 4.4LIMITING REAGENT PROBLEMS
Definition
LIMITING REAGENT: reactant that limits the amount of product formed in a reaction
Ex.

18. 4.4LIMITING REAGENT PROBLEMS
Steps to solving
Choose 1 product to convert to.
Figure out how many moles of that product will be formed based on the amounts of each reactant (2 steps/problems).
SMALLER amount of product determines the limiting reactant.
Find the # grams if needed
Limiting Reagents Movie Clip

19. 4.4LIMITING REAGENT PROBLEMS
Ex4.6 What is the theoretical yield of product for the following reaction if one starts with 1.20 moles of aluminum and 2.40 moles of iodine? Which reagent is in excess, and by how many moles?
2Al(s) + 3I2(s)  2AlI3

20. 4.4LIMITING REAGENT PROBLEMS
Ex4.7 Solve according to the reaction and equation in Ex. 4.6, but starting with 1.20g Al and 2.40g I2.

21. 4.4LIMITING REAGENT PROBLEMS
Percent Yield – the percent actually produced based on the calculated theoretical yield
Percent yield = actual yield x 100%
theoretical yield

22. 4.4LIMITING REAGENT PROBLEMS
Ex4.8 For the following reaction, what is the theoretical yield of product when 6.00g of phosphorus is treated with 25.0g iodine. If the actual yield of product is 22.5g, then what is the percentage yield?
P I2  PI3

23. 4.4LIMITING REAGENT PROBLEMS
Ex4.9 Methane (CH4) reacts with chlorine to produce chloroform (CHCl3) and HCl. In and industrial process, 2.00 x 103kg of methane is treated with 2.00 x 104kg of chlorine and 1.03 x 104kg of chloroform is produced. How many more kg of the limiting reagent would be needed to completely use up all the other reactant?

24. 4.5 PERCENT YIELD
Ex4.10 Nitric oxide, NO, is made from the oxidation of NH3 and is represented by the equation:
4NH3(g) + 5O2(g)  4NO(g) + 6H2O(l)
An 8.50g sample of NH3 and excess oxygen produces 12.0g of NO. What is the percent yield of NO?

25. 4.5 PERCENT YIELD
Ex4.11 An ester was formed by heating 20.0g of ethanol, C2H5OH, with excess acetic acid, CH3COOH, to yield 21.8g of ethyl acetate, CH3COOC2H5. What is the percent yield of ethyl acetate?
CH3COOH(l) + C2H5OH  CH3COOC2H5(l) + H2O (l)

26. 4.6 CHEMICAL EQUATIONS AND CHEMICAL ANALYSIS
Ex A 10.00g sample of an oxide of copper, when heated in a stream of an excess of hydrogen gas, forms 1.26 g of water. What is the percent copper by mass in the original compound? Determine the formula of the compound. Assume all the oxygen in the original compound is converted to water.

27. 4.6 CHEMICAL EQUATIONS AND CHEMICAL ANALYSIS
Ex4.13 Phenylfluoroform contains 57.54% carbon, 3.45% hydrogen, and 39.01% fluorine. The empirical formula is the same as the molecular formula. What is the number of carbon atoms in a molecule of phenylfluoroform?

28. 4.6 CHEMICAL EQUATIONS AND CHEMICAL ANALYSIS
Ex A 27.0g sample of an unknown carbon and hydrogen compound was burned in excess oxygen to form 88.0g carbon dioxide and 27.0g water. What is a possible molecular formula of this compound?

29. Ex4.15 A g sample of ascorbic acid, Vitamin C, was burned in a carbon-hydrogen combustion apparatus to produce g of CO2 and g of H2O. Ascorbic acid contains only carbon, hydrogen, and oxygen. Determine the masses of C, H, and O in the sample and then determine the empirical formula. In a separate experiment the molar mass of the ascorbic acid was found to be g/mol. What is the molecular formula?

30. END OF CHAPTER 4