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STOICHIOMETRY
Laws of Chemical Combination
Chemical reactions take place according to certain laws. These laws are called the Laws of
Chemical Combination. “These are no longer useful in chemical calculations now but gives an idea
of earlier methods of analysing and relating compounds by mass.”
v Law of Conservation of Mass [Lavoisier (1774)]
During any physical or chemical change, the sum of masses of all substances present in
reactions vessel remain conserved.
v Law of Constant Composition or Definite Proportions [Proust (1799)]
In a given chemical compound, the elements are always combined in the same proportions by
mass.
v Law of Multiple Proportions [Dalton (1803)]
Whenever two elements form more than one compound, the different masses of one element
that combine with the same mass of the other element are in the ratio of small whole
numbers.
v Law of Reciprocal Proportions [Richter (1792)]
When two elements combine separately with a fixed mass of a third elements then the ratio
of their masses in which they do so is either same or some whole number multiple of the ratio
in which they combine with each other.
v Gay-Lussac’s Law of combining volumes
According to Gay-Lussac’s law of combining volume, when gases react together, they always
do so in volumes which bear a simple ratio to one another and to the volumes of the products,
if these are also gases, provided all measurements of volumes are done under similar
conditions of temperature and pressure.
v Avogadro’s Law
The volume of a gas (at fixed pressure and temperature) is proportional to the number of
moles (or molecules of gas present). Mathematically we can write
V µn
Or Equal volumes of all gases under similar conditions of temperature and pressure contain
equal number of molecules.
For More Material Join: @JEEAdvanced_2024
,For More Material Join: @JEEAdvanced_2024
,For More Material Join: @JEEAdvanced_2024
, 1
1
STOICHIOMETRY
Laws of Chemical Combination
Chemical reactions take place according to certain laws. These laws are called the Laws of
Chemical Combination. “These are no longer useful in chemical calculations now but gives an idea
of earlier methods of analysing and relating compounds by mass.”
v Law of Conservation of Mass [Lavoisier (1774)]
During any physical or chemical change, the sum of masses of all substances present in
reactions vessel remain conserved.
v Law of Constant Composition or Definite Proportions [Proust (1799)]
In a given chemical compound, the elements are always combined in the same proportions by
mass.
v Law of Multiple Proportions [Dalton (1803)]
Whenever two elements form more than one compound, the different masses of one element
that combine with the same mass of the other element are in the ratio of small whole
numbers.
v Law of Reciprocal Proportions [Richter (1792)]
When two elements combine separately with a fixed mass of a third elements then the ratio
of their masses in which they do so is either same or some whole number multiple of the ratio
in which they combine with each other.
v Gay-Lussac’s Law of combining volumes
According to Gay-Lussac’s law of combining volume, when gases react together, they always
do so in volumes which bear a simple ratio to one another and to the volumes of the products,
if these are also gases, provided all measurements of volumes are done under similar
conditions of temperature and pressure.
v Avogadro’s Law
The volume of a gas (at fixed pressure and temperature) is proportional to the number of
moles (or molecules of gas present). Mathematically we can write
V µn
Or Equal volumes of all gases under similar conditions of temperature and pressure contain
equal number of molecules.
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