Stoichiometry LACC Chem 101 2 Review of Balancing

Stoichiometry LACC Chem 101

2 Review of Balancing Equations ¡ Balance the following chemical equations shown below: ____KCl. O 3(s) ____ KCl(s) + ____ O 2(g) ____ NH 3(g) + ____ O 2(g) ____ N 2(g) + ____ H 2 O(g) ____ Fe(s) + ____ H 2 O(g) ____ Fe 3 O 4(s) + ____ H 2(g) ____ H 2 S(g) + ____ SO 2(g) ____ H 2 O(l) + ____ S(s) LACC Chem 101

Reaction Stoichiometry 3 ¡ the numerical relationships between chemical amounts in a reaction is called stoichiometry ¡ the coefficients in a balanced chemical equation specify the relative amounts in moles of each of the substances involved in the reaction 2 C 8 H 18(l) + 25 O 2(g) 16 CO 2(g) + 18 H 2 O(g) 2 molecules of C 8 H 18 react with 25 molecules of O 2 to form 16 molecules of CO 2 and 18 molecules of H 2 O 2 moles of C 8 H 18 react with 25 moles of O 2 to form 16 moles of CO 2 and 18 moles of H 2 O 2 mol C 8 H 18 : 25 mol O 2 : 16 mol CO 2 : 18 mol H 2 O LACC Chem 101

Predicting Amounts from Stoichiometry 4 ¡ the amounts of any other substance in a chemical reaction can be determined from the amount of just one substance ¡ How much CO 2 can be made from 22. 0 moles of C 8 H 18 in the combustion of C 8 H 18? 2 C 8 H 18(l) + 25 O 2(g) 16 CO 2(g) + 18 H 2 O(g) 2 moles C 8 H 18 : 16 moles CO 2 LACC Chem 101

Finely divided sulfur ignites spontaneously in fluorine to produce sulfur 5 hexafluoride according to the following unbalanced equation: S(s) + F 2(g) SF 6(g) A. How many grams of SF 6(g) can be produced from 5. 00 g of sulfur? B. How many grams of fluorine are required to react with the 5. 00 g of sulfur? LACC Chem 101

Deuterated ammonia, ND 3(g), can be prepared by reacting lithium nitride with heavy water, D 2 O(l), according to the following equation: Li 3 N(s) + D 2 O(l) Li. OD(s) + ND 3(g) A. How many milligrams of heavy water are required to produce 7. 15 mg of ND 3(g)? Take the atomic mass of deuterium to be 2. 014 amu. B. Given that the density of heavy water is 1. 106 g/m. L at room temperature, how many milliliters of heavy water are required? LACC Chem 101 6

A frequently used method for preparing oxygen in the laboratory is by thermal decomposition of potassium chlorate according to the following unbalanced chemical equation: KCl. O 3(s) KCl(s) + O 2(g) How many grams of O 2 can be prepared from 30. 6 g of KCl. O 3(s)? LACC Chem 101 7

Consider the combustion of propane, C 3 H 8. A typical barbecue propane tank contains about 15 lbs of propane. How many grams of O 2 are 8 required to burn this quantity of propane? How many grams of CO 2 are produced? LACC Chem 101

Limiting Reagent 9 ¡ If more than one reactant used, the two (or three, etc) may notbe mixed in stoichiometric quantities ¡ Reactant that “runs out” if referred to as the limiting reagent ¡ Reactant still left over is referred to as an excess reactant ¡ Must determine which reactant is limiting before attempting a problem ¡ Done on a mole basis LACC Chem 101

The thermite reaction is a very high energy reaction, emitting large amounts of energy. A mixture is prepared from 25. 0 g of aluminum and 85. 0 g of Fe 2 O 3. The reaction that occurs is described by the following equation: Fe 2 O 3(s) + Al(s) Al 2 O 3(s) + Fe(l) How much iron is produced in the reaction? LACC Chem 101 10

Calcium sulfide can be made by heating calcium sulfate with charcoal at high temperature according to the following unbalanced chemical equation: Ca. SO 4(s) + C(s) Ca. S(s) + CO(g) How many grams of Ca. S(s) can be prepared from 100. 0 g each of Ca. SO 4(s) and C(s)? How many grams of unreacted reactant remain at the end of this reaction? LACC Chem 101 11

If 21. 4 g of solid zinc are treated with 3. 13 L 0. 200 M HCl, how many grams of hydrogen gas will theoretically be formed? How much of which reactant will be left unreacted? The products of this reaction are hydrogen gas and zinc chloride. LACC Chem 101 12

Percent Yield ¡ Even if enough reactants exists and reaction conditions are correct, some materials may remain unreacted ¡ Percent yield is the ratio of the actual yield of a product compared to the yield theoretically possible by mass: LACC Chem 101 13

Liquid tin(IV) chloride can be made by heating tin in an atmosphere of dry chlorine. If the percentage yield of this process is 64. 3%, then how many grams of tin are required to produce 0. 106 g of the product? LACC Chem 101 14

Aluminum burns in bromine, producing aluminum bromide. When 6. 0 g of aluminum was reacted with an excess of bromine, 50. 3 g of aluminum bromide was isolated. Calculate theoretical and percent yield of this reaction. LACC Chem 101 15

Workshop on Percentage Yield 16 1. A 0. 473 -g sample of phosphorus is reacted with an excess of chlorine, and 2. 12 g of phosphorus pentachloride is collected. What is the percentage yield of the product? 2. A century ago, sodium bicarbonate was prepared from sodium sulfate by a three-step process: Na 2 SO 4(s) + 4 C(s) Na 2 S(s) + 4 CO(g) Na 2 S(s) + Ca. CO 3(s) Ca. S(s) + Na 2 CO 3(s) + H 2 O(l) + CO 2(g) 2 Na. HCO 3(s) How many kilograms of sodium bicarbonate could be formed from one kilogram of sodium sulfate, assuming an 82% yield in each step? LACC Chem 101