CHAPTER 4:
CHEMICAL EQUATIONS AND
STOICHIOMETRY
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.
HOMEWORK
• #1 - 9, 11, 45, Worksheets in Packet
• Balancing Equations
• #2 - 13, 15, 17, 19, 47, 49
• Basic Mass Stoichiometry
• #3 - 21, 23, 25
• Limiting Reactants
• #4 - 27, 29, 31, 33, 35
• % Yield
• #5 - 37, 39, 43, 53, 55
• Empirical/Molecular Formulas from Stoich—HARD!!!!
• #6 - 51, 52, 57, 59, 61, 63, 65
• Summary Questions: EVERYTHING!
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)
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!!
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”
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
4.1 CHEMICAL EQUATIONS AND 4.2
BALANCING CHEMICAL EQUATIONS
5. Symbols used in chemical equations:
(s)
catalyst
(ℓ)
electricity
(g)
UV light
(aq)
∆
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
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
4.3 MASS RELATIONSHIPS IN CHEMICAL
REACTIONS: STOICHIOMETRY
2. Coefficients can stand for:
**Moles**
Atoms
Molecules
Formula Units
NOT grams!!
theoretical yield:
the amount of product
that “should” be produced
based on the available
amounts of reactants
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.
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?
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?
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?
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?
4.4LIMITING REAGENT PROBLEMS
•
Definition
•
LIMITING REAGENT: reactant that limits the amount
of product formed in a reaction
•
Ex.
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
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
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.
4.4LIMITING REAGENT PROBLEMS
• Percent Yield – the percent actually
produced based on the calculated
theoretical yield
Percent yield = actual yield x 100%
theoretical yield
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?
P4 + I2  PI3
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?
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?
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)
4.6 CHEMICAL EQUATIONS AND
CHEMICAL ANALYSIS
•
Ex4.12 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.
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?
4.6 CHEMICAL EQUATIONS AND
CHEMICAL ANALYSIS
•
Ex4.14 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?
•
Ex4.15 A 0.1247g sample of ascorbic acid, Vitamin C, was burned in a
carbon-hydrogen combustion apparatus to produce 0.1869g of CO2 and
0.0510g 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 180 + 10 g/mol. What is the molecular formula?
END OF CHAPTER 4