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Title: STOICHIOMETRY 2: Chemical Equations and Reaction Stoichiometry.
Description: Teaches how to handle Calculations in Stoichiometry 2 (Calculations based on Chemical Reactions). It helps the student overcome one of the biggest challenges in Chemistry. Good for Students in high school and the first year in university. Highly simplified, written in simple language and lucid style for easy comprehension.
Description: Teaches how to handle Calculations in Stoichiometry 2 (Calculations based on Chemical Reactions). It helps the student overcome one of the biggest challenges in Chemistry. Good for Students in high school and the first year in university. Highly simplified, written in simple language and lucid style for easy comprehension.
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STOICHIOMETRY
2
CHEMICAL EQUATIONS
AND
REACTION STOICHIOMETRY
by
Temple C
...
A chemical equation shows the chemical formulas and
the amounts of the reacting substances (reactants) and the chemical formulas
and the amounts of the substances formed (products)
...
The number written by the side of each substance represents the number of
moles of the substance involved in the reaction
...
Reaction stoichiometry deals with the quantitative relationships between
substances in chemical reactions
...
Let us consider the general requirements for handling calculations
based on chemical equations
...
Eke)
...
Case 1: Solids and Gases
The number of moles of a pure solid or gas is given by the ratio of its given
mass to its molar mass
...
In symbols,
...
The molar concentration of a solution is the number of moles of the solute per
(per unit volume) of the solution
...
In symbols,
where
molar concentration in
volume of the solution in
, and
...
Solution:
Molar concentration of the solution,
Volume of the solution,
...
With
...
Example 2: Number of moles in an Aqueous Solution
Find the number of moles present in
hydrochloric acid
...
Molar concentration of the solution,
Volume of the solution,
The number of moles,
With
...
...
MOLAR VOLUME OF A GAS
, we have
The molar volume,
is the volume occupied by one mole of any gas at
Standard Temperature and Pressure (STP)
...
i
...
Let us now study some illustrative examples
...
Example 3: Mass of a Product Formed: Mass-Mass Relationship
Calcium trioxocarbonate (IV),
decomposes when heated according to
the equation:
...
(b) Mass of
liberated
...
We then find the amount of the substances
formed from the given mass of
...
From the balanced equation of the reaction,
1 mole of
produces 1 mole of
...
By simple proportion,
...
From the balanced equation of the reaction,
1 mole of
produces 1 mole of
Using the molar masses,
...
By simple proportion,
Example 4: Number of moles of a Product Formed: Mass-Mole
Relationship
How many moles of Hydrogen gas would be formed when
of
Magnesium ribbon reacts with excess Hydrochloric acid according to the
equation;
Solution:
Molar mass of
From the equation of the reaction,
,
1 mole of
produces 1 mole of
Using the molar mass of
,
...
...
This generally involves the use of the
balanced equation of the reaction
...
More illustrative examples of such calculations are presented
...
Example 5: Moles of a Reactant Required: Mole-Mole Relationship
How many moles of potassium trioxochlorate (V),
must be heated to
give
mole of Oxygen according to the reaction:
?
Solution:
From the equation of the reaction,
,
moles of
are produced by moles of
By simple proportion,
moles of
will be reproduced by
mole of
...
mole of
...
Solution:
Mass of
Molar mass of
The equation of the reaction is:
...
at STP,
By simple proportion,
...
...
By simple proportion,
Example 8: Aqueous Solution: Mass-Mole Relationship
Calculate the mass of Magnesium oxide that would react completely with
of
Hydrochloric acid according to the equation:
...
The required mass of
is then obtained by
simple proportion after establishing the stoichiometric relationship between
and
according to the equation of the reaction
...
Molar mass of
From the balanced equation of the reaction,
,
moles of
react with mole of
...
By simple proportion,
...
...
of
given
...
viz ;
Hence, the volume of
(b) Volume of
Molar concentration of
The number of moles of
required as
required is
...
,
From the balanced equation of reaction,
, we
,
...
, the
Example 10: Solution Stoichiometry: Mole-Mole Relationship
Hydrochloric acid,
reacts with Sodium hydroxide,
, according to the
equation:
...
The number of moles of
Molar concentration of
Let the volume of
...
...
This is the number of moles of
that that reacts with
From the equation of the reaction,
...
Thus,
Hence, the required volume of
is
...
Calculate the:
(a) molar concentration of
...
Solution:
Volume of
Molar concentration of
Volume of
Let the molar concentration of
From the equation of the reaction,
,
By simple proportion,
Since the required number of moles of
, we have
(b) The mass of
produced
...
,
Using the molar mass of
By simple proportion,
,
Example 12: Solution Stoichiometry: Volume of Gas Liberated
completely reacted with
according to the
equation:
...
(b) the volume of
produced at STP
...
Volume of
Molar concentration of
...
Molar concentration of
...
Number of moles of
...
From the balanced equation of the reaction,
,
...
But the required number of moles of
is
...
From the equation of the reaction,
,
...
By using the molar volume,
THE LIMITING REACTANT CONCEPT
Generally, a balanced equation of a chemical reaction establishes the
stoichiometric amounts of the reactants required to completely react with
each other
...
Stoichiometric calculations are usually based on the limiting reactant
and not on the reactant present in excess
...
Example 13: Limiting Reactant: Mass-Mass Relationship
Calculate the mass of
formed when
reacts with
according to the reaction:
...
We first determine the limiting reactant
and then establish the stoichiometric relationship between the limiting
reactant and
...
Solution:
Mass of
Mass of
Molar mass of
Molar mass of
Molar mass of
...
...
...
Number of moles of
...
Hence, the limiting reactant is
...
Solution:
As in the previous example, we first determine the limiting reactant
...
Mass of
Molar mass of
...
Molar mass of
...
Number of moles of
...
From the balanced equation of the reaction:
,
...
Now, we take advantage of the stoichiometric relationship between
and
...
Solution:
Masses used in stoichiometric calculations must be expressed in grams
...
Mass of
...
...
By simple proportion,
...
Hence, the limiting reactant is
...
By simple proportion,
Hence, the mass of iron produced
...
Solution:
Mass of Mg given
...
...
...
By simple proportion,
...
Since there are
available,
Hence,
is the limiting reactant
...
Using the molar volume,
of
...
...
This is known
as the theoretical yield
...
Generally, the actual yield is always less than the theoretical yield
...
When
of Benzene was mixed with excess
,
of
Nitrobenzene was isolated
...
Principle and Concept:
We use the balanced equation of the reaction to find the mass of
Nitrobenzene produced when
of Benzene reacts with
...
By comparing this with the actual yield, the percent yield can
easily be found
...
Molar mass of
From the balanced equation of the reaction,
,
...
Using the molar masses,
...
The actual yield
(given in the question)
...
Example 18: Actual Yield from Percent Yield
Phosphorus (III) chloride reacts with Chlorine to form Phosphorus (V) chloride
according to the equation:
...
Solution:
The mass of
expected is the actual yield
...
Molar mass of
...
This gives the theoretical yield
...
Using the molar masses,
...
...
Hence, the mass of
expected is
...
What mass of
must be heated in order to produce
of
?
Solution:
Percent yield
Actual (expected) yield
Let the theoretical yield
...
We have
The question then is “What mass of
of
?”
Molar mass of
Molar mass of
The balanced equation of the reaction is
...
Using the molar masses,
...
that must be heated is
...
Usually, a product from one reaction
becomes the starting material for the next reaction
...
Let us study some examples of calculations on sequential reactions
...
Solution:
Molar mass of
...
Since the second equation represents the burning of methane, we use it to
determine the amount of Oxygen required to burn
of Methane
...
Using the molar mass of
,
...
...
...
By simple proportion,
...
Example 21: Sequential Reactions: Production of Slaked Lime
Given the sequence of reactions:
(i)
, and
(ii)
,
what mass of slaked lime,
would be obtained starting from
of marble,
?
Principle and Concept:
An inspection of the given equations shows that
is common to both
reactions
...
We then use this amount with the second equation to
find the mass of
produced
...
...
produced from the first reaction:
...
Using the molar mass of
,
...
Example 22: Sequential Reactions: Double Evolution of CO
Carbon (IV)oxide,
is liberated on strong heating of Potassium
trioxocarbonate (IV),
according to the equation:
...
Using the given sequence of reactions, calculate the total volume of
measured at STP that can be obtained from
of
...
Given mass of
...
Using the molar mass of
, and the molar volume,
By simple proportion,
To calculate the volume of
produced in the second reaction, we must
know the mass of
formed from the first reaction
...
Solution:
Mass of
...
...
By using simple proportion,
...
Example 23: Purity of Samples; Mass-Mole Relationship
What mass of Calcium trioxocarbonate (IV),
which is only
pure
would react completely with
according to the reaction:
?
Solution:
Molar mass of
...
...
...
Using the molar mass of
,
By simple proportion,
Since
the bulk
is only
impure
Hence, the mass of
pure, we use simple proportion to find the mass of
...
required is
...
Calculate the volume of
required to soften hard water
containing
...
...
...
...
,
...
By simple proportion,
Since the required number of moles of
form a simple linear equation
...
Example 25: Solution Stoichiometry; Neutralization of Excess Acid
was treated with excess
...
What was the original volume of the acid?
Solution:
Let the original volume of the acid,
Molar concentration of
...
...
This is the original number of moles of
...
Molar mass of
Given mass of
...
...
Using the molar mass of
,
...
Next, we determine the number of moles of
reaction
...
Molar concentration of
...
The equation of the second reaction is:
...
By simple proportion,
...
Since the remaining number of moles of
from the first reaction reacts
with
in the second reaction, we form the linear equation:
Hence, the original volume of the acid
...
You have learned:
1
...
The given mass, molar mass, molar concentration,
and volume of a solution are usual parameters
...
of any gas at STP occupies a volume of
This is known as the molar volume,
...
3
...
The required
amount is found by using a simple proportion
...
The extent of any chemical reaction is dictated by the limiting reactant
...
5
...
6
...
It serves to link the reactions
...
I hope it has helped you to have a
better understanding of the topic
...
(Stoichiometry 1: Chemical Formulas
and Composition Stoichiometry)
...
Eke)
...
Eke
...
Eke
Title: STOICHIOMETRY 2: Chemical Equations and Reaction Stoichiometry.
Description: Teaches how to handle Calculations in Stoichiometry 2 (Calculations based on Chemical Reactions). It helps the student overcome one of the biggest challenges in Chemistry. Good for Students in high school and the first year in university. Highly simplified, written in simple language and lucid style for easy comprehension.
Description: Teaches how to handle Calculations in Stoichiometry 2 (Calculations based on Chemical Reactions). It helps the student overcome one of the biggest challenges in Chemistry. Good for Students in high school and the first year in university. Highly simplified, written in simple language and lucid style for easy comprehension.