Chemistry 103 Lecture 16
Dec 15, 2015
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, C8H18, a
component of gasoline, proceeds as follows
C8H18 + O2 ------> CO2 + H2O
(unbalanced)
Stoichiometry Problems continued…The complete combustion of octane, C8H18, a component
of gasoline, proceeds as follows
2C8H18 + 25O2 ------> 16CO2 + 18H2O
Stoichiometry Problems continued…The complete combustion of octane, C8H18, a component
of gasoline, proceeds as follows
2C8H18 + 25O2 ------> 16CO2 + 18H2O
How many moles of O2 are needed to burn 1.25 moles
of C8H18?
Stoichiometry Problems continued…The complete combustion of octane, C8H18, a component
of gasoline, proceeds as follows
2C8H18 + 25O2 ------> 16CO2 + 18H2O
How many grams of O2 are needed to burn 10.0 grams
of C8H18?
Limiting Reactant
What is the limiting reactant when 2.00g of Na and 2.00g of Cl2 combine as follows:
2Na + Cl2 -----> 2NaCl
Problem continued….
How many grams of the remaining reactant would be left over once the reaction has run to completion? 2Na + Cl2 ----> 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)
Limiting Reactant
If 4.80 grams Ca are mixed with 2.00 grams N2, how many grams of the remaining reactant are left over after the reaction has run to completion?
3Ca(s) + N2(g) Ca3N2(s)
Limiting Reactant
If 4.80 grams Ca are mixed with 2.00 grams N2, how many grams of the remaining reactant are left over after the reaction has run to completion?
3Ca(s) + N2(g) Ca3N2(s)
Limiting Reactant
If 4.80 grams Ca are mixed with 2.00 grams N2 and the reaction has a 69.2% percent yield, what is the actual yield (in grams)?
3Ca(s) + N2(g) Ca3N2(s)
More LR problems
Methanol (CH3OH) is used as a fuel in racing cars. It burns in the engine according to the equation:
2CH3OH + 3O2 ----> 2CO2 + 4H2O
If 7.82 x 1023 molecules of methanol are mixed with 46.0g of O2, what is the mass of CO2 produced?
a). 57.2g b). 42.2g c). 63.3g
Learning CheckWithout proper ventilation and limited oxygen, the reaction of carbon and oxygen produces carbon monoxide.
2C(g) + O2(g) 2CO(g)
What is the percent yield if 40.0 g CO are produced when 30.0 g O2 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) + O2(g) 2MgO(s)
2Na(s) + Cl2(g) 2NaCl(s)
SO3(g) + H2O(l) H2SO4(aq)
A B A B
Decomposition
In a decomposition reaction, • One substance splits into two or more simpler substances
2HgO(s) 2Hg(l) + O2(g)
2KClO3(s) 2KCl(s) + 3 O2(g)
Single Replacement
In a single replacement reaction, • One element takes the place of a different element in a
reacting compound
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)
Double Replacement
In a double replacement, • Two elements in the reactants exchange places
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
ZnS(s) + 2HCl(aq) ZnCl2(aq) + H2S(g)
In a combustion reaction,
• A compound such as carbon reacts with oxygen, O2
C(s) + O2(g) CO2(g)
CH4(g) + 2O2(g) CO2 (g) + 2H2O(g)
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)
• Fuels burned in oxygen produce CO2, H2O, and energy.
Combustion
Learning Check
Identify each reaction as: 1) combination 2) decomposition 3) combustion4) single replacement 5) double replacement
A. 3Ba(s) + N2(g) Ba3N2(s)
B. 2Ag(s) + H2S(aq) Ag2S(s) + H2(g)
C. SiO2(s) + 4HF(aq) SiF4(s) + 2H2O(l)
D. PbCl2(aq) + K2SO4(aq) 2KCl(aq) + PbSO4(s)
E. K2CO3(s) K2O(aq) + CO2(g)
F. C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g)
Limiting Reactant
Ethylene burns in air according to the following unbalanced equation:
C2H4(g) + O2(g) -------> CO2(g) + H2O(l)
a. How many grams of CO2 will be formed when a mixture of 2.93g of C2H4 and 4.29g of O2 combine?
Limiting Reactant
Ethylene burns in air according to the following unbalanced equation:
C2H4(g) + 3O2(g) -------> 2CO2(g) + 2H2O(l)
a. How many grams of CO2 will be formed when a mixture of 2.93g of C2H4 and 4.29g of O2 combine?