Some Basic Concepts of Chemistry 2 Flashcards
What is the Law of Conservation of Mass?
This law was put forth by Antoine Lavoisier
in 1789. He performed careful experimental
studies for combustion reactions and reached
to the conclusion that in all physical and
chemical changes, there is no net change in
mass duting the process. this was the result of exact
measurement of masses of reactants and
products, and carefully planned experiments
performed by Lavoisier.
state law of conservation of mass?
Law of conservation of mass states that in a chemical reaction, matter is neither created not destroyed. In all physical and chemical changes, the total mass of the reactants is equal to the mass of products.
what is the law of definite proportions?
This law was given by, a
French chemist, Joseph
Proust. Proust worked with two
samples of cupric carbonate
— one of which was of natural
origin and the other was synthetic. He found
that the composition of elements present in it
was same for both the samples.
, he concluded that irrespective of the
source, a given compound always contains
same elements combined together in the same
proportion by mass. The validity of this law
has been confirmed by various experiments.
It is sometimes also referred to as Law of
Definite Composition.
State the Law of Constant Composition/Definite Composition/ Definite proportions
A pure chemical compound is always found to be made up of the same elements combined together in the same fixed proportion by mass
Justify the law of constant composition/definite composition/definite proportions
CO2 may be prepared in lab as follows:
CaCO3 —heat—> CaO+ CO2
C+O2—heat—> CO2
CaCO3 + 2HCl—–> CaCl2 + H2O + CO2
2NaHCO3—heat—> Na2CO3 + H2O + CO2
In all these cases, CO2 is made up of the same elements ie Crbn and oxygen combined in the same fixed proportion by mass which is 12:32 or 3:8
limitations of law of constant proportion
It is not applicable if an element exists in different isotopes which may be involved in the formation of the compound. The elements may combine in the same ratio but the compounds formed may be different.
Law of constant proportions does not hold true if the different isotopes of the element are not involved in chemical compound.
Example - For making CO2 gas, C-12 combines with O in ratio C:O::12:32 while C-14 carbon isotope combines in the ratio C:O::14:32.
State law of multiple proportion
If two elements can combine to form more than one compound, the masses of one element that combines with the fixed mass of the other element, are in a ratio of small whole numbers.
justify law of constant proportion with examples
hydrogen combines with
oxygen to form two compounds, namely, water
and hydrogen peroxide.
Hydrogen + Oxygen → Water
2g 16g 18g
Hydrogen + Oxygen → Hydrogen Peroxide
2g 32g 34g
Here, the masses of oxygen (i.e., 16 g and 32 g),
which combine with a fixed mass of hydrogen
(2g) bear a simple ratio, i.e., 16:32 or 1: 2.
State Gay Lussac’s Law of Gaseous Volumes
When gases combine and are produced in a chemical reaction, they do is a simple ratio by volume, provided all gases are at the same temperature and pressure.
justify gay lussac’s law with example.
Thus, 100 mL of hydrogen
combine with 50 mL of
oxygen to give 100 mL of
water vapour.
Hydrogen + Oxygen → Water
100 mL 50 mL 100 mL
Thus, the volumes of hydrogen and
oxygen which combine (i.e., 100 mL and
50 mL) bear a simple ratio of 2:1.
State Avogadro’s Law
Equal volumes of gases, at the same temperature and pressure, contain the same number of molecules.
What are the applications of Avogadro’s Law
-finding the atomicity of elementary gases.
- Molecular mass= 2 x vapour density
How did avogadro’s law explain atomicity of elemenatary gases
Avogadro
could explain the above result
by considering the molecules
to be polyatomic. If hydrogen
and oxygen were considered
as diatomic as recognised
now, then the above results
are easily understandable.
However, Dalton and others
believed at that time that
atoms of the same kind cannot combine and molecules of oxygen or
hydrogen containing two atoms did not exist.
Postulates of Dalton’s atomic theoyr
In 1808, Dalton published
‘A New System of Chemical
Philosophy’, in which he
proposed the following :
1. Matter consists of indivisible atoms.
- All atoms of a given element have identical
properties, including identical mass. Atoms
of different elements differ in mass. - Compounds are formed when atoms of
different elements combine in a fixed ratio. - Chemical reactions involve reorganisation
of atoms. These are neither created nor
destroyed in a chemical reaction.
