Title: Chemical Stoichiometry Reacting Quantities and Material Balance
1Chemical StoichiometryReacting Quantities
andMaterial Balance
- Edward A. Mottel
- Department of Chemistry
- Rose-Hulman Institute of Technology
2Resources Available
- Zumdahl Chapter 3.5-3.8
- 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.
3Chemical 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 of hydrogen
peroxide to give water and oxygen.
4Hydrogen PeroxideDecomposition
5- Concentrated hydrogen peroxide contains 30
hydrogen peroxide by weight and the balance
water. The density of 30 hydrogen peroxide is
1.110 gmL-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.
6- 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 0.9970gcm-3.
- The density of pure hydrogen peroxide is 1.442
gcm-3.
7volume of 30 H2O2
mass of empty bottle
8mass of 30 H2O2 solution
mass of H2O2 in solution
volume of 30 H2O2
?
36/68
32/68
initial mass of bottle solution
mass of H2O in original solution
mass of O2 produced
mass of H2O produced
mass of empty bottle
volume of H2O at end
final mass of bottle solution
total mass of H2O at end
9Problem Solving Format
- Define the problem
- Outline the solution to the problem
- include relevant diagrams equations
- Solve the problem
10Stoichiometry
- 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.
1119th Century Chemistry
3 grams of carbon
4 grams of oxygen
Analyzed reactions using weights and volumes
12Stoichiometry Rules
- Law of Conservation of Mass
- Law of Constant Composition
- Law of Multiple Proportions
13Law of Conservation of Mass
In a chemical reaction, mass is neither created
nor destroyed.
14Law of Constant CompositionLaw of Definite
Proportions
Any sample of a pure compound always consists of
the same elements combined in the same
proportions by mass.
C(s) O2(g) ? CO2(g)
15Compounds which contain only carbon and
hydrogen are called hydrocarbons.
A hydrocarbon is burned in oxygen and
produces 0.400 grams of water and 0.782 grams of
carbon dioxide.
What is the empirical formula of the hydrocarbon?
What was the original mass of the
hydrocarbon that was combusted?
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17Law of Multiple Proportions
If two elements combine to form more than one
stable compound, the masses of one element that
combines with a fixed mass of the second
element will be in the ratio of small whole
numbers.
C(s) 1/2 O2(g) ? CO (g)
12 g C and 16 g O2
C(s) O2(g) ? CO2(g)
12 g C and 32 g O2
18Chemical 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 oxygen are reacted
to give carbon dioxide, which is the limiting
reactant?
19Chemical 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 when 120 grams of
carbon reacts with 120 grams of oxygen to give
carbon dioxide?
20Chemical 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
carbon reacts with 120 grams of oxygen to give
200 grams of carbon monoxide?
Show how your results support the Law of
Conservation of Mass.
21mass of carbon
moles of carbon
balanced equation
limiting reagent
mass of oxygen
moles of oxygen
balanced equation
moles of CO possible
actual mass of CO
percentage yield
MW of CO
mass of CO possible
22Reaction 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.
23Reaction of Methane and Carbon Dioxide
24Challenge
- 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.
25Limestone
- Limestone is a naturally occurring material
consisting principally of calcium carbonate. - Upon heating (roasting) at gt1000 C, it
decomposes into calcium oxide and carbon dioxide. - You are the chief engineer. How could you
determine when this roasting process is
completed?
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28mass of 30 H2O2 solution
mass of H2O2 in solution
volume of 30 H2O2
70 H2O by mass
36/68
32/68
balanced equation
initial mass of bottle solution
mass of H2O in original solution
mass of O2 produced
mass of H2O produced
mass is conserved
mass is conserved
mass of empty bottle
volume of H2O at end
final mass of bottle solution
total mass of H2O at end
29Reaction of Methane and Carbon Dioxide