Class 11 States of Matter Notes
States of Matter
1) 1) Three different states of matter ( solid, liquid,
gas ) :
Solid is that state of matter with a definite
shape and volume.
Liquid has a definite volume but no
definite shape
Gas has neither a definite shape nor volume
2) 2) Two more states of matter :
a)
Plasma state which consists of a mixture of
electrons and positivity-charged ions formed due to the superheating of gases
b)
Supercooled solid state in which atoms lose
their identity to form a single super-atom.
It intermolecular forces >> thermal energy, the substance
exists as solid.
Its thermal energy >>
intermolecular force, the substance exists as a gas
If there is a reasonable balance between the two, the substance
is liquid
6 ) Gaseous state: Measurement of mass, volume, pressure,
and temperature
1)
Mass: it is usually, expressed in moles
2)
Volume: 1L = 103
3)
Pressure: atmospheric pressure is
measured with a barometer while the pressure of a gas is measured with a manometer.
Pressure , p = hρg
where h = height of mercury column , ρ = density of
mercury , g = acceleration due to
gravity,
1 atm = 76 cm = 760mm = 760tor
4) Temperature : -273.15*C = 0 K or 0*C = 273.15 K
7 ) Gas laws:
V inversely proportional to p at constant T or PV = constant
we conclude that Pd. At altitude, as P is low, hence d' is
low, i.e., less O, is available for breathing. This is called altitude
sickness.
2 (2 ) Charle's law: Pressure remaining constant,
volume of a given mass of a gas increases or decreases by 1 / 273 of its volume
at 0°C for every one-degree rise or fall of 273 kelvin temperature. Hence v1 = T, pressure
remains constant, and the volume of a given mass of gas are direct.
proportional to its absolute temperature. This means that V1
/ T1 =V2 / T2 at constant P as V = KT, the plot of V versus T will be linear
passing through the origin.
(3) Gay-Lussac's
Pressure: Temperature law: Similar to Charles' law, at constant volume,
(4) Avogadro's law: Under similar conditions of temperature and pressure, equal volumes of all gases contain an equal number of molecules, e.g., 22.4 L of any gas at 0°C (273.15 K) and 1 atmospheric pressure contains Avogadro's number (6.022 x 10) molecules. These are old STP conditions. Now, STP conditions, Now STP usually used are 0°C and 1 bar pressure. Then, the molar volume is 22.7 L. If ambient STP conditions are used viz. 25°C (298.15 K) and 1 bar pressure, molar volume = 24.789 L = 24.8 L.
(5) Ideal gas equation: It represents the simultaneous effect of
temperature and pressure on the volume of a gas. The equation is P1V1 / T1 =
P2V2/T2 = constant = R, gas constant. Hence, PV = RT for 1 mole of the gas or
PV = nRT for n moles of the gas.
(6) Dalton's law of partial pressures: If two or more gases that
do not react chemically with each other are enclosed in a vessel, then total
pressure exerted by the gaseous mixture is the sum of their partial pressure,
ie., P = p, + P₂+ + Thus, if a gas is collected over water, P. moist gas =P dry
gas +Aqueous tension at that temperature.
(7) Graham's law of diffusion/effusion: Under similar conditions of temperature and pressure, rates of diffusion/effusion of different gases are inversely proportional to the the square root of their densities.
(9) Ideal and Real gases: A gas that obeys the ideal gas
equation under all conditions of temperature and pressure is called an ideal
gas. However, the concept of an ideal gas is only hypothetical. The gases obey
gas laws only if pressure or temperature is low. Such gases are called real
gases.
8) Compressibility factor (Z): The extent of deviation of a
real gas from ideal behaviour is PV expressed in terms of compressibility
factor (2) viz. Z= pv/ not
For ideal gas, Z= 1. For real gases, Z is not 1. When Z < 1, the gas is said to show-ve
deviation. When Z> 1, it shows a +ve deviation. Gases like CO, CO2, CH4,
etc. show →ve deviations at low pressure and +ve deviation at high pressure
whereas H2, and He shows +ve deviation at all pressures. For gases showing - ve
deviation, the deviation decreases with the increase of temperature. The
temperature at which a real gas behaves like an ideal gas over an appreciable
pressure range is called Boyle temperature
Thus, For a real gas, Z= pv/ not
Z = Vreal / Videal
10) Causes of deviation from the ideal behavior: Real gases
show deviation from ideal behavior at low temperatures or high pressure. This
is because under these conditions.
(1) Forces of attraction or repulsion among molecules may
not be negligible.
(2) The volume occupied by molecules may not be negligible compared
to the total volume of the gas.
11) Equation of state for real gases-van der Waal's equation: Applying correction to pressure and volume, the equation obtained is ( p + a/ v2 )(V-b)=Rt where 'a' and 'b' are called van der Waals constants.
12) Significance of van der Waal's constants: 'a' is a
measure of the magnitude of attractive forces whereas 'b' is a measure of the
effective size of the gas molecules, b = 4v where v is the actual volume of 1
mole of gas molecules, 'b' is called excluded volume or co-volume.
13) Why do H, and He show only +ve deviation?: H, and He is very small in size. Intermolecular forces of attraction in them are negligible, i.e... der Waals equation becomes a V2 is negligible. Hence, VA P(V-b) RT or PV = RT + Pb or PV RT 1+ RT ie. Z=1+
Thus, Z increases continuously with the increase of P
14) Liquefaction of gases and critical temperature: A gas can
be liquefied by cooling the gas or applying pressure on the gas or the combined
effect of both. However, for every gas, there is a particular temperature above .which a gas cannot be liquefied howsoever high pressure we may apply on the
gas. This temperature is called critical temperature (T). The corresponding
pressure and volume are called critical pressure (P) and critical volume (V).
15) Andrews experiments on critical phenomena: Taking CO, and
gas, Andrews studied the effect of pressure on volume at different constant
temperatures. Each plot of P versus Vat constant T is called an isotherm. From
these isotherms, he determined the values of TP and V for CO. These were
30.98°C, 73.9 atm, and 95.6 mL mol.
16) Relation between critical temperature and van der Waals
constant 'a': Greater the critical temperature, the more easily the gas can be
liquefied. The greater the value of van der Waals constant a', the greater the
intermolecular forces and hence more easily the gas can be liquefied. Thus 'a'
increases in the same order as critical temperature. For example, He and H,
have low values of 'T' and 'a' and hence are difficult to liquefy whereas CO,
NH, and SO, have a high value of 'T' and 'a' and are easy to liquefy.
→Factors affecting vapor pressure:
(1) Nature of the liquid: Weaker are the intermolecular forces, higher is the pressure.
(2) Temperature: Higher the temperature, the greater the vapor
pressure. If P, and P₂ are vapour pressures at temperatures T, and T₂, then by
Clausius-Clapeyron equation.
(3) Boiling point: It is the temperature at which the vapor
pressure of the liquid becomes equal to external pressure. When external
pressure = 1 atm = 760 mm, it is called the normal boiling point.
18) Surface tension of liquids: It is the force acting at right angles to the surface along one centimetre length of the surface. Its units are dynes cm¹ or Nm
19) Surface energy of a liquid: It is the work required to
be done to extend the surface area of the liquid by 1 sq. cm or 1 sq. m. Its
units are ergs cm² or J m². The spherical shape of drops, fire polishing of
glass, and rise of a liquid in a capillary tube are all due to the force of
surface tension.
→Factors affecting surface tension:
(1) Nature of the liquid: Greater the intermolecular forces of attraction, the higher is the surface tension.
(2) Temperature: Surface tension decreases with the increase in temperature because of kinetic energy increases and hence intermolecular attraction decreases
20) Viscosity of liquids: It is the internal resistance of a
liquid to flow or it is the force of friction that one part of the liquid
offers to another part of the liquid. For two layers each of surface area A cm,
separated by distance dx cm and having velocity difference dv cm s
→Factors affecting viscosity :