Chemistry Chapter (2) Gaseous State

                                                    

POINTS TO REMEMBER

• Matter exists in four states i.e. solid,liquid,gas and plasma.
• The simplest form of matter is the gaseous state.
• Gases don’t have definite shape and volume.
• Their molecules move rapidly in all directions in a random way . So, they occupy the whole space open to them.
•   There are large empty spaces between molecules.
•  Gases can diffuse and effuse.
• Gases can be compressed by applying pressure.
• Gases can be expand on heating or by increasing the available volume.
• When sudden expansion of gases takes place ,it is called Joule Thomson effect.
• The molecules collide with one another and with the walls of container with perfectly elastic collisions.
• Because of negligible inter molecular forces, the gases have low densities.
• Gases or their mixtures are homogeneous.
• Gases can be liquefied,if subjected to low temperatures or high pressures.

Boyle’s Law: 

At constant temperature, volume of a given mass of a gas is inversely proportional to the pressure applied on it.

  ·       The isotherm of CO₂ was first studies by Andrews.

Charle’s Law:

At constant pressure, the volume of a given mass of a gas is directly proportional to the absolute temperature.

  ·    Zero of the absolute scale corresponds to – 273^oC.

  ·       The graph that show the variation of volume of the gas with absolute temperature at constant pressure is called isobar or isoplestics.

Gay –Lussac’s Law or Amonton’law: 

At constant volume, the pressure of a given mass of a gas is directly proportional to the absolute temperature.

 ·   The variation of the pressure of gas with absolute temperature at constant volume is called isochore.

 ·       Ideal gas equation holds good at low pressure and high temperature.

 ·       A gas which obeys gas laws completely at all conditions of temperature and pressure is called ideal or perfect gas.

 ·    Non-ideal or real gases behaves ideally at high temperature and low pressure.

  ·       Gram Molar Volume: 

     The volume occupied by one mole of an ideal gas at STP is equal  to 22.4 dm² .22.4 dm² is known as Gram molar volume.

  ·       The value of gas constant (R) for one molecule of a gas is called Boltzmann constant (K).

  ·       Thus K=1.38 x 10^-16 erg mole^-1 degree^-1 J mole^-1 degree^-1..

  ·       Dalton’s Law of Partial Pressure: 

   When two or more gases which do not react chemically are kept in a close space ,the total pressure exerted by the mixture is equal to the sum of the partial pressure of individual gases.

 ·   The pressure due to water vapour at a given temperature is known as aqueous tension or saturated water vapour pressure.

  ·       Pressure of dry gas= Total pressure – aqueous tension.

  ·       Graham’s Law of Diffusion: 

     At constant temperature and pressure, the rate of diffusion of gas is inversely proportional to the square root of its density.

  ·       Lighter gases diffuse faster than heavier gases.

  ·       The volume of a gas diffused per unit time is called the rate of diffusion.

  ·       Avogadro’s Law: 

   Equal volume of ideal gases at the same temperature and pressure contain equal number of molecules.

  To calculate the pressure or volume of a real gas under the non-ideal conditions,alternative kinetic equation has been developed.This is known as the vander waal’s Equation.

Plasma

  ·       Plasma is a substance in which many of the atoms or molecules are effectively ionized allowing charges to flow freely.

  ·       Most of the universe consists of the matter in the plasma state. The ionization is caused by high temperatures or by radiation.

  ·       Plasma is a conductor of electricity and it has unique physics  compared to solids, liquids,and gases.

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