States Of Matter
· Water exists in three
state i.e. solid (ice), liquid (portable water), gas (steam, vapors).
· In these three states
water has different physical properties but same chemical composition i.e. H_{2}O
· Also characteristics of
these states of water depend on the molecular energy and how molecules
aggregate.
· As molecules change its
physical state (from liquid to gas, gas to liquid, solid to gas etc.) there is
no change in chemical properties of the substance but some changes may occur in
rate of chemical reaction.
Intermolecular Forces:
These
are forces of attraction and/or repulsion between the interacting particles
i.e. atom or molecules.
Dutch Scientist J. Van der Waals
(1837-1923) explains deviation of the real gases from ideal behavior with intermolecular
forces, so intermolecular forces are also called as van der waals forces.
Example: Hydrogen bonding which is
strong dipole-dipole interaction.
Dispersion Forces:
If an atom gets
instantaneous dipole (i.e. Atom has more electron density in right or left hand
side) then its nearby atom become induced dipole, so these two temporary dipole
attract each other. This attraction force is known as dispersion forces.
· As these forces were first
proposed by F. London so these forces are also known as London forces.
Dipole-Dipole Forces:
This type of force act
between the molecules which have permanent dipole. Dipole of these molecule
possess some partial charges (denoted by delta that is delta positive ^{} or delta negative^{})
Example: HCl molecule, where H
possess delta positive and Cl possess delta negative.
Dipole-Induced Dipole Forces:
These attractive forces
act between polar and non-polar molecules where polar molecules have permanent
dipole, which induced the dipole and non-polar molecule by deforming electronic
cloud of non-polar molecule.
· As polarisability
increases, strength of the attractive interaction also increases.
Hydrogen-Bond:
It is a type of dipole-dipole
interaction present in molecules with high polar N-H, O-H and H-F bonds.
Thermal Energy:
It is the energy of the
body arise due to the motion of its atoms and molecules.
·
Thermal energy is directly proportional to temperature of the
substances.
Intermolecular forces v/s
Thermal interactions
·
Intermolecular forces make molecules of the substance keep
together.
·
While thermal energy of the substance make molecules keep
apart.
·
These two (thermal energy and intermolecular forces) decides
collectively the states of matter.
·
If intermolecular forces predominance then
Gas->Liquid->Solid
·
If thermal energy predominance then
Solid->Liquid->Gas
What is Troposphere:
It is the lowest layer
of the atmosphere held to surface of the earth by gravitational forces where we
live. It contains O_{2}, CO_{2}, N_{2} and water vapors
etc.
Gaseous State:
Only 11 elements ( H, O,
N, F, Cl, He ,Ne, Ar, Kr, Xe, Rn exists in gaseous state under normal
conditions.
Characteristic Physical Properties
Of Gases
·
Gases are highly compressible.
·
Gases exert the equal pressure in all direction.
·
As compared to solid and liquids, gases have much lower
density.
·
Gases don’t have definite (fix) shape and volume.
·
Gases mix completely and evenly in all proportions.
Gas Laws
Boyle’s law:
It is also known as
Pressure Volume relationship.
As per Boyle’s law, ”At
constant temperature and fixed amount of gases in no. of moles, its pressure
varies inversely with its volume.”
Mathematically, at
constant T and n,
P1/V ……………..1
P = k_{1} x 1/V = k_{1}/V
………..2
Where, P = Pressure, V = Volume and k =
proportionality constant and value of k_{1} depends upon Pressure P and
Volume V.
Also,
K_{1} = PV ………..3
According to above relation, product of
pressure P and volume V remains constant, if we fixed the amount of gas at
constant temperature. You read these first class chemistry notes for classes 11
at online classes by www.ChemistryNotesInfo.com.
So, P_{1}V_{1
}= P_{2}V_{2 }= Constant
………4
Then,
P_{1}/ P_{2 }= V_{2}/V_{1 }……………..5
As we know, Density is equal to mass divided
by volume i.e. d=m/V
So, V = m/d …………6
From equation 2 & 6,
P = k_{1}d/m
·
d
= (m/k_{1})/P = k’P ……………7
Where, k’ = m/k_{1}
Charle’s Law:
This is also known as
Temperature and Volume relationship.
As per Charle’s law, “At
constant pressure and fixed mass of gas, Volume is directly proportional to
Absolute temperature.”
Mathematically, at
constant P and n,
V T
Also, V=k_{2}T
Where, K_{2} is a
constant.
Thermodynamic Scale:
Kelvin scale of the Temperature is known as
the Thermodynamic Scale which is utilized in many scientific works.
Kelvin Scale:
To obtain temperature in
Kelvin scale we add 273.15 (generally 273) in Celsius temperature.
i.e. K= 273.15 + °C (degree Celsius)
Gay Lussac’s Law:
This law is also known
as Pressure and Temperature relationship.
According to Gay Lussac’s
Law “At constant Volume and fixed amount of gas, pressure is directly
proportional to temperature.”
Mathematically, at
constant V and n,
P T
Also, P=k_{3}T
Where, K_{3} is a
constant.
Avogadro’s Law:
This law is also known
as Volume and amount relationship.
According to Avogadro’s
law “Equal volume of all the gases under same condition of pressure and
Temperature contain equal no. of molecules.”
V n ………….1
V=k_{4}n ……………2
Where, V is volume, k_{4}
is a constant and n is no. of moles of gas.
Avogadro’s Constant:
One mole has 6.022x10^{23}
no. of molecules which is called as Avogadro’s constant. As we know, mole is
equal to mass divided by molar mass.
So n = m/M ……………..3
Then from equation 2 &
3
V = k_{4}(m/M)
M = k_{4}. m/V
M = k_{4}.d {here . represents multiplication}
Where M is molar mass, m
is mass and V is volume, K_{4} is constant and d is density.
Ideal Gas Equation:
Combination of 3 laws (Boyles
Law, Charles Law and Avogadro law) gives a single equation (PV=nRT) called as
Ideal gas equation.
Mathematically,
According to Boyle’s Law;
at constant T and n,
V 1/P ……….1
According to Charles Law;
at constant P and n,
V T ……….2
According to Avogadro Law;
at constant T and n,
V n ……….3
From equation 1, 2 and 3;
we get,
V nT/P ……….4
Or, V =R nT/P ……….5
Also, PV = nRT …………..6
Then, R = PV/nT ………..7
Where, R is a gas constant
which is same for all gases and known as Universal Gas Constant
and equation 6, PV = nRT is known as Ideal Gas Equation.
Equation Of State:
Ideal gas equation is
also known as equation of state because it gives relationship between 4
variables i.e. P, V, n and T. which describes state of any gas.
Let if pressure, volume and temperature of fixed
amount of ideal gas changes from P_{1}, V_{1}, T_{1} to
P_{2}, V_{2}, T_{2}
then,
P_{1}V_{1}/T_{1}
= nR …………..8
P_{2}V_{2}/T_{2}
= nR …………..9
So, from equation 8 &
9, we get
P_{1}V_{1}/T_{1}
= P_{1}V_{1}/T_{1} ………..10
This above equation (eq.
10) is called Combined Gas Law.
Density And Molar Mass Of
Gaseous Substances:
As per Ideal Gas Equation,
PV=nRT
Then, n/V = P/RT
On replacing n by m/M (as
mole n= mass m/ molar mass M); we obtain,
m/MV=P/RT
On replacing m/V by
density d; we obtain,
d/M=P/RT
Also, on rearrangement,
M = dRT/P
Where, M is molar mass, d
is density, R is gas constant, T is temperature and P is pressure.
Dalton Law Of Partial
Pressure:
According to Dalton law of
partial pressure, “Total exerted pressure by mixture of all non-reactive gases
is equal to the sum of partial pressure of all individual gases.”
At constant temperature T
and Volume V
P_{total} = p_{1} +p_{2}
+p_{3}…………..
Where, P_{tolal} =
total exerted pressure of mixture of all gases.
p_{1}, p_{2},
p_{3 }etc. is pressure exerted by individual gases known as partial
pressure.
Aqueous Tension:
It is exerted by the
saturated water vapors.
P_{drygas} = P_{total}
– Aqueous Tension
Partial Pressure In Terms
Of Mole Fraction:
Let at T temperature, 3 gases of Volume V exert the partial pressure
p1, p2, p3. Then as per ideal gas equation,
p_{1}=n_{1}RT/V
p_{2}=n_{2}RT/V
p_{3}=n_{3}RT/V
Where,
n_{1}, n_{2}, n_{3} are no. of moles.
Also, according to Daltons law of partial
pressure
P_{total} = p_{1}
+p_{2} +p_{3}
Or, P_{total} = n_{1}RT/V + n_{2}RT/V + n_{3}RT/V
= (n_{1}+n_{2}+n_{3})RT/V
And,
on dividing p_{1} by P_{Total }, we obtain
P_{1}/
P_{Total}={n_{1}/(n_{1}+n_{2}+n_{3})}{RTV/RTV}
P_{1}/
P_{Total}=n_{1}/(n_{1}+n_{2}+n_{3}) = n_{1}/n
= x_{1}
Where,
n= n_{1}+n_{2}+n_{3} and x_{1} is mole fraction
of first gas.
So,
p_{1}=x_{1}P_{Total}
Similarly,
p_{2}=x_{2}P_{Total}
P_{3}=x_{3}P_{Total}
Then,
general equation is written as-
P_{i}=x_{i}P_{Total}
Where,
p_{i }is partial pressure of i^{th} gas.
x_{i
}is mole fraction of i^{th} gas.
Kinetic Molecular Theory
Of Gases:
The postulates or assumption of Kinetic molecular theory of the gases are as follows:
- ·
Gases contain atoms or molecules, as large no. of identical
particles. These atoms or molecules are at large distances from each other, so
that volume of gases is very high as compared to actual Volume of all molecules
of gases. ‘Great compressibility of the gases is explained by these assumptions’.
- ·
Gases occupy all available space by expansion because at
ordinary pressure and temperature there are no attractive forces between gas
particles.
- ·
Gas particles always move in random and at constant motion
because if gas particles are at rest and they occupy fixed positions then gas
would have fixed shape, which is not observed at all.
- ·
Gas particles move in straight lines in all the possible
directions. During random motion these particles collide with each other and
also collide with the walls of the container of the gas. As a result of this
collision of gas particles with wall of the gas container pressure is exerted
by gas.
- ·
Collision between the gas molecules is perfectly elastic. It
means total energy of the molecules don’t change that is It remains same before
and after collision. Individual energy of the molecules may change due to
exchange of energy between the colliding molecules, but sum of energies of all
molecules remains same.
- ·
Molecules of the gas move with the different speeds and their
individual speed goes on changing due to collision of molecules but at
particular temperature, distribution of speeds of molecules remains constant.
- ·
Kinetic energy of molecules (of the gas) is directly
proportional to absolute temperature because on heating gas at fixed volume,
its pressure increases. As on heating molecules moves with more speed and
strike with walls of the container more rapidly, so exerts more pressure.
Behavior Of Real Gases
Deviation From Ideal Gas
Behavior:
When we do different experiments, we find that real gases don’t follow PV=nRT
Equation of ideal gases. So real gases don’t follow Boyle’s law means, if we
plot graph between PV and P then we don’t get parallel straight line at all
pressures with X-axis.
Graph
Real gases in above graph
show some significant deviation from ideal gas behavior. As we see-
1) Dihydrogen and helium
shows positive deviation means PV value increases with increase in pressure.
2) Methane and Carbon
monoxide shows negative deviation and positive deviation means first with
increase in pressure, PV value decreases and reaches the minimum then starts
increasing with increasing pressure.
- ·
Real gases don’t follow Boyle’s law, Charles law and Avogadro’s
law perfectly under the all conditions, So real gases liquefy when they cooled
and compressed.
- ·
Under very high pressure attraction forces start operating
between molecules of gases so pressure exerted by real gases is lower than that
of ideal gas, because in ideal gas there is no attraction force exists at high
pressure.
P_{ideal}=P_{real}+(an^{2}/V^{2})
…………..1
P_{real} =
observed pressure
an^{2} /V^{2}
= correction term
Where ‘a’ is constant
- ·
Under very high pressure gas molecule don’t move freely but
restricted to (V-nb) Volume, Where nb is actual Volume occupied by the gas
molecules themselves. So we can write gas equation for real gases as :
{P+(an^{2}/V^{2})}(V-nb)=nRT
…………2
Equation 2 is known as van
der walls equation.
Where n is no. of moles of
the gas.
a and b is vander walls
constant and value depends on gas characteristics.
- ·
Deviation from ideal behavior from real gases is measured
with compressibility factor z.
Compressibility factor,
z = PV/nRT
…………3
If z =1 gas is ideal gas
because PV = nRT
If z > 1 or z<1, gas
is real gas and If z > 1 then it is more difficult to compress gas.
- ·
Boyle’s temperature or Boyle’s point is a temperature at
which real gas behaves like ideal gas under appreciable range of pressure.
- ·
Compressibility factor is also defined as ratio between
actual molar volume and calculated molar volume
i.e. z = V_{real} / V_{ideal}
As per above discussion we
say that gases behave ideally -
- 1. At low temperature and
high pressure.
- 2. or, If volume occupied by
the gas is very large therefore volume occupied by gas molecule can be
neglected in comparison to it.
Liquification Of Gases
·
The process of converting gas into liquid is known as liquification
of gas
·
The highest temperature at which gas start liquefying is known
as critical temperature (T_{c})
·
Volume of one mole of the gas at this critical temperature is
known as critical volume (V_{c})
·
Pressure at this critical temperature is known as critical pressure
(P_{c})
·
Gases are cooled below their critical temperature for the
liquefication of gases
·
When we apply cooling as well as compression, gases liquefy easily
Liquid State
Intermolecular forces in
liquids are stronger than in gases. Liquid have definite (fix) volume and they
can flow and take the shape of the container in which these liquids are stored.
These online education classes degree notes are published by
ChemistryNotesInfo.com and hosted at ChemistryNotesInfo.blogspot.com Vapour pressure,
viscosity, surface tension are some physical properties of liquids which are
described below-
Vapor Pressure:
Pressure exerted by the
vapors on the walls of the container containing liquid is known as vapour
pressure.
·
Vaporization depends on temperature
· Vapour pressure at which equilibrium is achieved between
liquid phase and vapor phase is known as Saturated Vapour Pressure
or Equilibrium Vapour Pressure
·
Boiling is a condition of free vaporization means vapor
extends freely into the surroundings.
·
Boiling temp. at 1 atm pressure is known as Normal
Boiling Point
·
Boiling temp. at 1 bar pressure is known as Standard
Boiling Point
·
Temp. at which clear boundary between liquid and vapors
disappear is known as Critical Temperature
Surface Tension:
Liquids tends to minimize
their surface area because molecules of the liquid on the surface experience
net attractive force towards the interior of the liquid, this characteristic
property of the liquid is known as Surface Tension.
Example: Mercury do not
form thin film and capillary action
Viscosity:
It is a measure of
resistance to flow that arise due to internal friction between the layers of
liquid (or fluid), when they slip over one another, during the flow of liquid
or fluid.
·
Force required to maintain flow of liquid layers is-
F=Adu/dz
Where, A is area of
contact,
du/dz is velocity
gradient,
is coefficient of viscosity.
SI unit of is “Newton second per
square meter (Nsm^{-2})”
cgs unit of is “poise”
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