Chemistry 103 Lecture 16

Outline I. Stoichiometry - Limiting Reactant - Percent Yield III. Classification of Reaction Types EXAM II - Thursday, July 3rd

Stoichiometry Chemical Stoichiometry: using mass and quantity relationships among reactants and products in a chemical reaction to make predictions about how much product will be made.

Stoichiometry Problems continued… The complete combustion of octane, C 8 H 18, a component of gasoline, proceeds as follows C 8 H 18 + O > CO 2 + H 2 O (unbalanced)

Stoichiometry Problems continued… The complete combustion of octane, C 8 H 18, a component of gasoline, proceeds as follows 2C 8 H O > 16CO H 2 O

Stoichiometry Problems continued… The complete combustion of octane, C 8 H 18, a component of gasoline, proceeds as follows 2C 8 H O > 16CO H 2 O How many moles of O 2 are needed to burn 1.25 moles of C 8 H 18 ?

Stoichiometry Problems continued… The complete combustion of octane, C 8 H 18, a component of gasoline, proceeds as follows 2C 8 H O > 16CO H 2 O How many grams of O 2 are needed to burn 10.0 grams of C 8 H 18 ?

Chemical Reactions Limiting Reactant & Percent Yield

Copyright © 2008 by Pearson Education, Inc. publishing as Benjamin Cummings

Limiting Reactant What is the limiting reactant when 2.00g of Na and 2.00g of Cl 2 combine as follows:  2Na + Cl > 2NaCl

Problem continued…. How many grams of the remaining reactant would be left over once the reaction has run to completion? 2Na + Cl > 2NaCl

Theoretical, Actual, and Percent Yield Theoretical yield The maximum amount of product calculated using the balanced equation (Solving the Limiting Reactant Problem). Actual yield The amount of product obtained when the reaction takes place. Percent yield The ratio of actual yield to theoretical yield. percent yield = actual yield (g) x 100 theoretical yield (g)

Back to our NaCl Problem If the actual yield of NaCl is 2.29g, what is the percent yield?

Limiting Reactant If 4.80 grams Ca are mixed with 2.00 grams N 2, how many grams of the remaining reactant are left over after the reaction has run to completion? 3Ca(s) + N 2 (g)  Ca 3 N 2 (s)

Limiting Reactant If 4.80 grams Ca are mixed with 2.00 grams N 2, how many grams of the remaining reactant are left over after the reaction has run to completion? 3Ca(s) + N 2 (g)  Ca 3 N 2 (s)

Limiting Reactant If 4.80 grams Ca are mixed with 2.00 grams N 2 and the reaction has a 69.2% percent yield, what is the actual yield (in grams)? 3Ca(s) + N 2 (g)  Ca 3 N 2 (s)

More LR problems Methanol (CH 3 OH) is used as a fuel in racing cars. It burns in the engine according to the equation: 2CH 3 OH + 3O > 2CO 2 + 4H 2 O If 7.82 x molecules of methanol are mixed with 46.0g of O 2, what is the mass of CO 2 produced? a). 57.2gb). 42.2g c). 63.3g

Learning Check Without proper ventilation and limited oxygen, the reaction of carbon and oxygen produces carbon monoxide. 2C(g) + O 2 (g) 2CO(g) What is the percent yield if 40.0 g CO are produced when 30.0 g O 2 are used? A) 25.0% B) 75.0% C) 76.2%

Chemical Reactions Types of Reactions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Combination In a combination reaction, Two or more elements form one product Or simple compounds combine to form one product + 2Mg(s) + O 2 (g) 2MgO(s) 2Na(s) + Cl 2 (g)2NaCl(s) SO 3 (g) + H 2 O(l)H 2 SO 4 (aq) ABAB

Formation of MgO

Decomposition In a decomposition reaction, One substance splits into two or more simpler substances 2HgO(s) 2Hg(l) + O 2 (g) 2KClO 3 (s) 2KCl(s) + 3 O 2 (g)

Decomposition of HgO

Single Replacement In a single replacement reaction, One element takes the place of a different element in a reacting compound Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Fe(s) + CuSO 4 (aq)FeSO 4 (aq) + Cu(s)

Zn and HCl Is a Single Replacement Reaction

Double Replacement In a double replacement, Two elements in the reactants exchange places AgNO 3 (aq) + NaCl(aq)AgCl(s) + NaNO 3 (aq) ZnS(s) + 2HCl(aq)ZnCl 2 (aq) + H 2 S(g)

Example of a Double Replacement

In a combustion reaction, A compound such as carbon reacts with oxygen, O 2 C(s) + O 2 (g) CO 2 (g) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) C 3 H 8 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O(g) Fuels burned in oxygen produce CO 2, H 2 O, and energy. Combustion

Example of a Combustion Reaction

Learning Check Balance the combustion equation. ___ C 5 H 12 + ___O 2 ___CO 2 + ___H 2 O

Summary of Reaction Types

Learning Check Identify each reaction as: 1) combination 2) decomposition 3) combustion 4) single replacement5) double replacement A. 3Ba(s) + N 2 (g) Ba 3 N 2 (s) B. 2Ag(s) + H 2 S(aq)Ag 2 S(s) + H 2 (g) C. SiO 2 (s) + 4HF(aq) SiF 4 (s) + 2H 2 O(l) D. PbCl 2 (aq) + K 2 SO 4 (aq) 2KCl(aq) + PbSO 4 (s) E. K 2 CO 3 (s) K 2 O(aq) + CO 2 (g) F. C 2 H 4 (g) + 3O 2 (g) 2CO 2 (g) + 2H 2 O(g)

Limiting Reactant Ethylene burns in air according to the following unbalanced equation: C 2 H 4 (g) + O 2 (g) > CO 2 (g) + H 2 O(l) a. How many grams of CO 2 will be formed when a mixture of 2.93g of C 2 H 4 and 4.29g of O 2 combine?

Limiting Reactant Ethylene burns in air according to the following unbalanced equation: C 2 H 4 (g) + 3O 2 (g) > 2CO 2 (g) + 2H 2 O(l) a. How many grams of CO 2 will be formed when a mixture of 2.93g of C 2 H 4 and 4.29g of O 2 combine?

Problem continued…. b. How many grams of each reactant would be left over once the reaction has run to completion?