Chapter 2: Gaseous State and Liquid State

Chapter 2: Gaseous State and Liquid State

Chapter 2: Gaseous State and Liquid State – Quick Revision/Short Notes

High Yield Facts

  • 1 mole =. 6.023 x 1023 molecules

= 22.4L of gas at NTP/STP

  • 1 atom = 760mmHg = 760 torr = 105Pascal (N m-2)

= 1.01 Barr

1 mm =1 torr; 1 atm= 1 Barr

  • R = 0.032L atm k-I mol-I

= 8.314Jk-1mol-1

= 8.314 Nm k-1 mol-1

= 8.314 x 1O7Erg k-1mol-1

= 1.99 Cal mol-1k-1

  • Gas constant for a single molecule is called Boltzmann constant (k)

  • Boyle’s Law: At constant temperature, V is inversely proportional to P i.e. PV=constant

or, P1V1=P2V2

Further, V is inversely proportional to d

Where,

V=Volume, d=density, V=Volume

Thus, d is directly proportional to P ( at constant temperature and mass ) i.e. d/P=constant

or, d1/p1 = d2/p2

 

Graphs: (At constant temperature)

  • P vs V is rectangular hyperbola

  • P vs 1/V is Straight line

  • P vs PV or V vs PV is a straight line with parallel to pressure and Volume axis respectively.

 

  • The graphs of’ Boyle’s law are called isotherms.

Note: Pressure of a pure gas is measured by manometer while that of a mixture of gases by a barometer.

 

  • Charle’s Law:

At constant pressure; V is directly proportional to T

Keeping volume constant P is directly proportional to T

At constant pressure, the volume of given mass of a substance changes by 1/273 of its Volume at 0°C for each degree of change in temperature.

Where, V= Volume, T= Temperature

  • At -273oC, volume or given gas becomes zero (i.e. its, gaseous state does not exist),
  • this is called absolute Zero temperature.
  • Actually, before the temperature of -273°C is reached, all gases become liquid to which Charle’s law does not apply.
  • At absolute , zero, temperature, the volume, pressure, kinetic energy and heat content of a gas is zero.
  • A plot between volume of the gas against absolute temperature at Constant pressure is known as isobar, it is always straight line.
  • For a definite of the gas, a plot of V vs T (k) at constant pressure is a straight line passing through the origin.

  • A plot of v vs T (‘_’C) at constant pressure is a straight line cutting the temperature axis at -273°C.

 

  • The gas equation: (Relation between A pressure, volume and temperature of a gas): This equation combines the Boyle’s

and Charle’s laws.

R= universal gas constant for ‘n’ mole of gas, the equation becomes PV=nRT

For initial and final pressure, volume and temperature,

  • Dalton‘s law or partial pressure:

Total Pressure (P) = Sum of individual partial pressure exerted by a mixture of gases

P=p1+p2+p3+……. pn

Criteria > The gases mixture should contain non-reacting gases.

  • SO2 and Cl2, NH3 and HCl do not obey Dalton’s law of partial pressure because they react with each other.
  • Partial pressure (p) = Mole fraction x Total pressure

P1 = n1/ n1+n2+…. + nn x P

No. of moles (n) = mass (m) / Molecular mass (M)

 

  • Graham’s law of diffusion of gases;

Rate of diffusion is inversely proportional to square root of Vapor density (d)

  • Kinetic Theory of Gases:

Postulates:

  • Molecules are in constant motion in all direction.
  • Molecular volume negligible as compared to total volume.
  • Collision between gas molecules is perfectly elastic.
  • Pressure exerted by gas due to collision of gas molecules with vessel walls.
  • No effective intermolecular force of attraction.
  • Eav directly proportional to T
  • Molecular speed:

  • Vander Waal’s equation:

Where, a = coefficient of intermolecular attraction

b= excluded volume per mole

Units of a= atm lit2 mol-2 or Pa m6 mol-2

b= lit mol-1 or m3 mol-1

 

  • Liquid State:
  • Surface tension: force acting at right angles to surface of liquid along 1 cm length of surface, which makes the liquid surface behaves as a stretched surface.

Surface tension increases with decreases in temperature.

Unit of Surface Tension is Jm-2 or Nm-1 (dyne cm-1)

  • Viscosity: the internal resistance to a liquid flow exerted by the layers of same liquid.

=> Increases with decrease in temperature.

3) Molarity (M): It is the number of moles of solute dissolved in 1000ml of solution.

For more quick revision short notes in Chemistry click HERE

 

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