XI ,CH-5 ,CHEMISTRY NOTES- STATE OF MATTER
STATE OF MATTER CH-5 XI
Matter & its states
Anythings which occupied space and have mass is called
matter.It divided mainly into three categories depending upon its physical
state namely solid, liquid and gaseous states.
Solids have a
definite volume and shape:
·
Definite shape and volume of the solids is
result of strong forces of attraction between its constituent particles which
keep them together in a fixed position and arrangement.
Liquids also have a definite volume but no definite
volume:
·
They take shape of the container in which
they are placed. This is due to relatively weaker force of attraction among the
particles of liquid.
Gases
have neither a definite volume nor a definite shape:
They fill the container completely in which they are
placed. This is due to the fact that the force of attraction among the
particles of liquids is almost zero and they are free to move independently to
each other.
#Attraction forces present between molecules
of state of matter
Intermolecular forces are the forces of attraction
and repulsion acting between interacting particles (atoms and
molecules).This term does not include the electrostatic forces
that exist between the two oppositely charged ions and the forces that
hold atoms of a molecule together i.e., covalent bonds.
A.Van-der Waals’ s forces
The attractive intermolecular forces are called vander Waals’
force. in honor of Dutch scientist Johannes van der Waals (1837-1923)
as he explained the deviation of real gases from the ideal behaviour
through these forces. It is very week force od attraction.
B.Dipole – Induced Dipole Interactions:
·
The electrons of neutral molecules keep on
oscillating w.r.t. the nuclei of atoms. As a result, at a given instant, one side
of the molecule may have a slight excess of electrons relative to the opposite
side. Thus a non – polar molecule may become momentarily self –
polarized.
·
This polarized molecule may induce a dipole
moment in the neighboring molecule. These two induced dipoles then attract each
other .These momentary dipole – induced dipole attractions are also
called London forces or dispersive forces.
The magnitude of these forces depends upon the following:
·
Size or molecular mass: The melting points and boiling
points of non – polar molecules increase as the size or molecular mass of the
molecule increases. For example, the m.p. and b.p. of alkanes, halogens,
noble gases etc. increase as the molecular mass of the molecule increases.
·
Geometry / Shape : For example, isomer n –
pentane has higher boiling point than neo – pentane because the former is zig –
zag chain with larger sites of contact and hence large intermolecular forces
whereas the latter is nearly spherical and hence has less contact and weaker
forces.
C.Dipole – Dipole Interactions:
·
In case of polar molecules, the vander waals’
forces are mainly due to electrical interaction between oppositively charged
ends of molecules called dipole – dipole interactions.
· Molecules have permanent dipole moments as a result of which there is appreciable dipole – dipole interactions between the molecules of these gases. The magnitude of this type of interaction depends upon the dipole moment of the molecule concerned. Evidently, greater the dipole moment, stronger is the dipole – dipole interactions. Because of these attractive forces, these gases can be easily liquefied.
D.Dipole – Induced Dipole Interactions:
·
A polar molecule may sometimes polarize a non
– polar molecule which lies in its vicinity and thus induces polarity in that
molecule just as a magnet induces magnetic polarity in a neutral piece of iron
lying close by the induced dipole then interacts with the dipole moment of the
First molecule and
thereby the two molecules are attracted together.
·
The magnitude of this interaction, evidently
depends upon the magnitude of the dipole moment of the polar molecule and the
polarizability of the non – polar molecule. The
solubility of inert gases in increases from He to Rn due to a
corresponding increase in magnitude of the dipole – induced dipole interactions
as the polarizability of the noble gas increases with increase in size from He
to Rn.
General Properties of Gases
Gases do not have definite shape and volume.Gases occupy the whole space
available to them Gases have unlimited dispensability and high compressibility.They
have very low densities because of negligible intermolecular forces. Gases exert pressure on the walls of the
container with perfectly elastic collisions.They diffuse rapidly through each
other from homogeneous mixture against the electric and gravitational field.
Parameters of Gases
The characteristics of gases are described in terms of following four
parameters
Mass,Volume,Pressure,Temperature
1. Mass (m):
The mass of the gas is related to the number of moles as
n = w/M Where n = number of moles w = mass of gas in grams
M = molecular mass of the gas
2. Volume (V):
Since gases occupy the entire space available to them, therefore the gas
volume means the volume of the container in which the gas is enclosed.
Units of Volume: Volume is
generally expressed in litre
(L), cm3 & dm3
1m3 = 103 litre = 103 dm3 = 106 cm3.
3. Pressure:
Pressure of the gas is due to its collisions with walls of its container i.e. the
force exerted by the gas per unit area on the walls of the container is equal
to its pressure.
Pressure is exerted by a gas due to kinetic energy of its molecules.As
temperature increases, the kinetic energy of molecules increases, which results
in increase in pressure of the gas. So, pressure of any gas is directly
proportional to its temperature.
Units of Pressure:
The pressure of a gas is expressed in atm, Pa, Nm–2, bar and lb/In2 (psi).
760 mm = 1 atm = 10132.5 KPa = 101325 Pa = 101325 Nm–2
760 mm of Hg = 1.01325 bar = 1013.25 milli bar = 14.7 lb/2n2 (psi)
3. Temperature (T):
Temperature is defined as the degree of hotness or coldness of a body.
The SI unit of temperature is Kelvin. oC and oF are
the two other units used for measuring temperature. On the Celsius
scale water freezes at 0°C and boils at 100°C where as in the Kelvin
scale water freezes at 273 K and boils at 373 K.
K = oC + 273.5 F = (9/5) oC +
32
Gases Laws
1.Boyle’s Law :
In 1662, Robert Boyle discovered that there existed a relation between
the pressure and the volume of a fixed amount of gas at a fixed temperature. In
his experiment, he discovered that the product of Pressure & Volume of a
fixed amount of gas at a fixed temperature was approximately a constant. So,
Boyle’s low states that ”At
constant temperature, the pressure of a fixed amount (i.e., number of
moles n) of gas varies inversely with its volume”.
Mathematically
It means that at constant temperature, product of pressure and
volume of a fixed amount of gas is constant.If a fixed amount of gas at
constant temperature T occupying volume V1 at pressure P1
undergoes expansion, so that volume becomes V2 and pressure
becomes P2,
then according to Boyle’s law :
then according to Boyle’s law :
Now,
Using Boyle’s Law we get,
1
atm = 1.01325 bar
A plot of P
versus 1/V at constant temperature for a fixed mass of
gas would be a straight line passing through the origin. And A plot of P versus V at constant
temperature for a fixed mass of a gas would be a rectangular hyperbola.
A plot of P (or V ) versus PV at constant temperature for a fixed mass of a gas is a straight line parallel to the PV axis.
2.Charles’s Law :
In 1787, Jacques Charles discovered that if the pressure is kept
constant, the volume of a gas sample increases linearly with the
temperature for a fixed amount of gas. This law led to the idea of temperature.
The unit of temperature used is Kelvin. Charles’s law
states that”At
constant pressure, the volume of a given mass of a gas is directly proportional
to its absolute temperature,,
Mathematically
Hence, if at constant pressure the volume of a gas V1 at
temperature T1 change
to V1 at
T2 we
have
V1/T1=V2/T2 This equation is known as Charle’s Law equation or
formula.
For each degree change in temperature, the volume of sample of a gas
changes by the fraction of 1/273.5 of its volume at 0 oC.
So,
This equation is known as Charles-Gay-Lussac
equation.
Where,Vt = volume of gas at temperature t OC V0 =
volume of gas at 0 OC
T = temperature in OC
The temperature of -273 OC, at which the volume of a gas
would theoretically be reduced to zero, is called absolute zero. At
absolute zero temperature, the volume, pressure, kinetic energy and heat
content of a gas is zero.
1. For a definite mass of the gas a plot of V vs T (oK)
at constant pressure is a straight line passing through the origin.
2. A plot of V
vs t
(oC) at constant pressure is a straight line cutting the temperature
axis at -273 oC
3.Gay-Lussac’s Law
This law states that “at
constant volume, the pressure of a given mass of a gas is directly proportional
to its absolute temperature”.
Mathematically
Where, P = Pressure of GasT= Absolute Temperature
If the pressure and temperature of a gas changes from P1
& T1
to P2
& T2 ,
volume remaining constant , we have
where, Pt = Pressure
of gas at t oC Po = Pressure
of gas at 0 oC
t = Temperature in oC.
4. Avogadro’s Law
In 1812, Amadeo Avogadro stated that
“Samples of different gases which contain the same number of molecules
(any complexity, size, shape) occupy the same volume at the same temperature
and pressure”.
It follows from Avogadro’s hypothesis that
(when T and P are constant).
Mathematically
Since volume of a gas is directly proportional to the number of
moles; one
mole of each gas at standard temperature and pressure (STP) will have
same volume.Standard temperature and pressure means 273.15
K (0°C) temperature and 1 bar (i.e., exactly 105 pascal)
pressure. At
STP molar volume of an ideal gas or a combination of ideal gases
is 22.71098 L mol–1
We know that number
of moles of any gas (n) = m/M
Where m = mass of the gas under investigation and M = molar mass
From Avogadro’s Law ,
Where, d = density of gas
#Ideal gas equation
We can conclude from equation that
the density of a gas is directly proportional to its molar mass.A gas
that follows Boyle’s law, Charles’ law and Avogadro law strictly is called
an ideal
gas. FOR DETAIL NOTES CONTACT- drsudhirtomar@gmail.comYOU TUBE ;-CHEMISTRY FREE ONLINE ADDA
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