CHAPTER 4: CHEMICAL EQUATIONS AND STOICHIOMETRY. 4.0OBJECTIVES Balance simple chemical equations and interpret the meaning of coefficients in the equation.

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:

STOICHIOMETRY2H2(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:

STOICHIOMETRY2. Coefficients can stand for:

**Moles** theoretical yield:Atoms the amount of

productMolecules that “should” be

producedFormula Units based on the available

amounts of reactants

NOT grams!!

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 PROBLEMSEx4.7 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 PROBLEMSEx4.8 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 YIELDEx4.11 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