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
= 8.314 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
Further, V is inversely proportional to d
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
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:
- 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.
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