Chemical StoichiometryReacting Quantities and
Material Balance
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
Resources Available
Fine, Beall & Stuehr: Chapter 3.5 A balanced chemical equation is used to
predict the maximum amount of product which can be formed in a chemical reaction.
Chemical nomenclature, molecular weight, mass and moles of each reactant present and product formed are concepts involved in these calculations.
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Chemical Equations
Stoichiometry (atom balance) Charge (charge balance) Format
• Phase annotation (s, l, g, aq)• Arrow notations
Write an annotated chemical equation for the
decomposition of a 30% solution ofhydrogen peroxide to give
water and oxygen.
Hydrogen PeroxideDecomposition
30%
H2O2
decomposesH2O
waterfrom decompositionand original water
2 H2O2(aq) 2 H2O(l) + O2(g)
70% water
Concentrated hydrogen peroxide contains 30% hydrogen peroxide by weight and the balance water. The density of 30% hydrogen peroxide is 1.110 g•mL-1.
Hydrogen peroxide decomposes upon standing, over a period of several months, to form water and oxygen.
Assume an empty 500 mL plastic bottle used to hold hydrogen peroxide has a mass of 100.0 grams.
30%H2O2
decomposesH2O
What would be the difference in mass and the percentage difference in mass between 500 mL of fresh 30% hydrogen peroxide in the 500 mL bottle and a bottle of hydrogen peroxide which is decomposed?
Assume any oxygen gas formed escapes. The density of water at 25.0 °C is
0.9970•g•cm-3. The density of pure hydrogen peroxide is
1.442 g•cm-3.
30%H2O2
decomposesH2O
volume of30% H2O2
density of30% H2O2
mass of30% H2O2
in solution
30% H2O2
by massmass of
H2O2
in solution
mass ofO2
produced
32/68balancedequation
mass ofH2O
produced
36/68
mass ofH2O
in originalsolution
30% H2Oby mass
total massof H2Oat end
mass isconserved
initial massof bottle
& solution
final massof bottle
& solution
mass ofemptybottle
volumeof H2Oat end
densityof H2O
mass isconserved
Problem Solving Format
Define the problem Outline the solution to the problem
• include relevant diagrams & equations Solve the problem
Stoichiometry
The study of heat, energy and material balances of a chemical system.• The amount of reactants and products in a
reaction are proportional to each other.• The amount of heat energy released or
required by a reaction is proportional to the amount of reactants and products involved in the reaction.
19th Century Chemistry
3 grams of carbon
4 grams of oxygen
400grams
300 grams
Analyzed reactions using
weights and volumes
Stoichiometry Rules
Law of Conservation of Mass Law of Constant Composition Law of Multiple Proportions
Law of Conservation of Mass
C(s) + O2(g) CO2(g)
12 g 32 g 44 g
In a chemical reaction, mass is neithercreated nor destroyed.
Law of Constant CompositionLaw of Definite Proportions
C(s) + O2(g) CO2(g)
12 g 32 g 44 g
6 g 16 g 22 g
3 g 8 g 11 g
Any sample of a pure compound alwaysconsists of the same elements combined in
the same proportions by mass.
Law of Multiple Proportions
C(s) + O2(g) CO2(g)
C(s) + 1/2 O2(g) CO (g) 12 g C and 16 g O2
12 g C and 32 g O2
If two elements combine to form more thanone stable compound,
the masses of one element that combineswith a fixed mass of the second element
will be in the ratio of small whole numbers.
16:32 is 1 to 2
Chemical Equations and Stoichiometry
Moles of reactants and moles of product• The balanced chemical equation deals
with molecules or moles, not grams Limiting reagent
• Every reaction that is complete (100% reaction) has at least one limiting reactant
If equal masses of carbon and oxygenare reacted to give carbon dioxide,
which is the limiting reactant?
Chemical Equations and Stoichiometry
Theoretical yield• The maximum number of moles or mass of
a product that could be formed from the given amounts of reactants
What is the theoretical yield when120 grams of carbon reacts with
120 grams of oxygen to give carbon dioxide?
Chemical Equations and Stoichiometry
Percentage yield• The amount of product formed divided by
the theoretical yield times 100%
What is the percentage yield if 120 grams of carbonreacts with 120 grams of oxygen
to give 200 grams of carbon monoxide?
Show how your results support theLaw of Conservation of Mass.
Reaction of Methane and Carbon Dioxide
50. grams of methane reacts with 50. grams of carbon dioxide to give carbon monoxide and water vapor.
If the reaction is 100% complete determine• the limiting reagent.• the mass of each reactant & product at the
end of the reaction.
Excel spreadsheet
Reaction of Methane and Carbon Dioxide
Challenge
Design a spreadsheet to determine the maximum amount of carbon dioxide that could be formed when any amount of sucrose (C12H22O11) reacts with any amount of oxygen gas. The other product is water.
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