. For the reversible reaction

N2(g) + 3H2(g)---> 2NH3(g) + heat .

The equilibrium shifts in forward direction:

A: by increasing the concentration of NH3(g)

B: by decreasing the pressure

C: by decreasing the concentrations of N2(g) and H2(g)

D: by increasing pressure and decreasing temperature


Best Answer


The correct answer is option D, which can be understood as follows:

According to Le Chatelier principle, when any equilibrium is disturbed by any change, it undergoes a change opposite to it to nullify the initial stimulus. 

So, if reactants, in this case , N2 and H2 are decreased, it will lead to production of more of them i.e shift reaction in backward direction. 

Similarly if the product(here ammonia)is increased,reaction will shift to backward direction to decrease the "increased ammonia".

Now if pressure is decreased,reaction will shift to direction where pressure will increase i.e where no.of moles increase( since P proportional to n), so reaction will shift backwards in this case. 

N2(g) + 3H2(g)---> 2NH3(g) + heat 

4 moles         2 moles

Conversely, if pressure is increased, reaction will shift forward to produce more ammonia. 

Similarly, in an exothermic reaction , decreasing temperature will lead to forward shift, since heat is released in the product side, so greater temperature there. 

Now if [NH3(g)] is increased(option A) , reaction will proceed in backward reaction (since increased product has to be compensated). 

If pressure is decreased(option B), converse to above explanation will occur and reaction will again proceed in backward direction. 

Upon decreasing conc. of reactants, N2 and H2, reaction will again shift to backward direction(To compensate the decreased reactants, Le Chatelier Principle). 

Final Answer:

Hence, the correct answer is option D i.e increasing pressure and decreasing temperature will lead to forward shift in this Haters reaction. 


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