basic-laws of chemcombi
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In the study of matter, we observe certain
phenomena which can be reproduced at will.These observed phenomena are called
scientific facts. Often, a large number of
scientific facts can be summarized into broad
or sweeping statements called laws.
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LAW OF CONSERVATION OF MASS
-which states that when an ordinary chemicalreaction occurs, there is no detectable change in
the masses of the substances involved before and
after the reaction.
masses of the reactants = masses of the products
before the reaction after the reaction
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LAW OF CONSERVATION OF MASS
However, Albert Einstein, a Nobel laureate
physicist and one of the most creative intellects in
human history, recognized the quantitative
interconversion of mass and energy in reactions,as shown by his famous equation.
E = mc
2
Where: E = energy
m = mass
c = velocity of light
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LAW OF CONSERVATION OF MASS
The interconvertibility of mass and energy holdstrue in energetic processes like radioactivity and
atomic explosions. Strictly speaking, the
interconversion of energy and mass cannot
possibly allow a constancy of one or the other.
However, the amount of energy and mass change
are too small to be detected in the laboratory.
Therefore, we can still count on the law ofconservation of mass for practical use.
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LAW OF DEFINITE PROPORTION
-states that a pure compound always contains the
same elements combined in the same proportions
by mass.
-when two elements combine to form a given
compound, they always do so in a fixedproportion.
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LAW OF DEFINITE PROPORTION
To illustrate the law of definite composition, refer
to the table
Trial Mass of C
(g)
Mass of O2(g)
Mass of CO2(g)
1
2
3
2.00
15.00
5.00
5.34
40.05
13.36
7.34
55.05
18.36
These are the mass data for the amounts of C,
O2, and CO2 in the reaction.
C + O2 CO2
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LAW OF DEFINITE PROPORTION
Trial Mass of C
(g)
Mass of O2
(g)
Mass of CO2
(g)
1
2
3
2.00
15.00
5.00
5.34
40.05
13.36
7.34
55.05
18.36
Find the percentages of carbon and oxygen.
% of C =
x 100
% of O =
x 100
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LAW OF DEFINITE PROPORTION
Trial Mass of C
(g)
Mass of O2(g)
Mass of CO2(g)
1
2
3
2.00
15.00
5.00
5.34
40.05
13.36
7.34
55.05
18.36
Trial 1 Trial 2 Trial 3
C =2.0
7.34 x 100
= 27.2%
O =5.34
7.34 x 100
= 72.8%
C =15.0
55.05 x 100
= 27.2%
O =40.05
55.05 x 100
= 72.8%
C =5.0
18.36 x 100
= 27.2%
O =13.36
18.36 x 100
= 72.8%
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LAW OF DEFINITE PROPORTION
Trial 1 Trial 2 Trial 3
C =2.0
7.34 x 100
= 27.2%
O =
5.34
7.34 x 100= 72.8%
C =15.0
55.05 x 100
= 27.2%
O =
40.05
55.05 x 100= 72.8%
C =5.0
18.36 x 100
= 27.2%
O =
13.36
18.36 x 100= 72.8%
These show that the percentage of carbon in CO2
which is 27.2% and the percentage of oxygen inCO2 which is 72.8% are definite.
The experimental data in the example also verify
and confirm the law of conservation of mass.
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LAW OF MULTIPLE PROPORTIONS
-this states that when two elements combine toform more than one compound, the masses of
one element which combine with a fixed mass of
the other element are in a ratio of small whole
numbers such as 2:1, 1:1, 2:3, etc.
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LAW OF MULTIPLE PROPORTIONS
Sample Exercise:Two different compounds elements C and D
were found to have the following compositions:
C D
First compound 2.276 g 0.792 gSecond compound 1.422 g 0.948 g
Find the formulas of the two compound.
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Solution: Mass may be fixed at C.
C D
First compound
2.276 g/2.276g = 1 0.792 g/2.276 g = 0.348
Second compound
1.422 g/1.422 g = 1 0.948 g/1.422 g = 0.667
Therefor, the formulas of the two compounds are:Ratio C D Formula
First 1 0.348/0.348 =1 CD
compound
Second 1 0.667/0.348 = 2 CD2compound
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Practice exercises
Find the formula of the compounds having the
following composition:X Y
First compound 50 g 56 g
Second compound 35 g 82 g
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