January 21, 2016

Junior Intermediate Chemistry - Imp Questions for 4 Marks

Q: Write any 4 postulates of Kinetic molecular theory of gases. (4 M)
A: Collisions of gas molecules is perfectly elastic. Average Kinetic energy of the gas molecules ∝ T. There is no force of attraction between the molecules of the gas at normal P and T. Gas molecules move in all possible directions in straight lines but randomly.

Q: State Le Chatlier's principle. Explain the effect of temperature and pressure on the synthesis of NH3 by Haber's process.

A: If a chemical reaction at equilibrium is disturbed either by change in pressure or concentration or temperature, then the system will be shifted towards the direction in which the change is nullified or minimised

Effect of P: By increasing pressure upto 200 atm, equilibrium will be shifted from 4 moles side to 2 moles side to form more NH3.

Effect of T: Forward reaction is exothermic. Increase in 'T' favours backward reaction, decrease in 'T' makes rate of forward reaction slow. So an optimum temperature 725 K to 775 K is used to get more NH3.

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