BHU PMT BHU PMT (Mains) Solved Paper-2008

  • question_answer

    Directions : In the following question more than one of the answers given may be correct. Select the correct answer and mark it according to the code:

    For the reaction \[{{C}_{6}}{{H}_{4}}(g)+{{H}_{2}}{{C}_{2}}{{H}_{6}};\]\[\Delta H=-32.7\,k\,cal\] The equilibrium concentration of\[{{C}_{2}}{{H}_{4}}\]can be increased by (1) decreasing the temperature (2) decreasing the pressure (3) removing some \[{{C}_{2}}{{H}_{6}}\] (4) removing some\[{{H}_{2}}\]

    A)  1, 2 and 3 are correct.

    B)  1 and 2 are correct.

    C)  2 and 4 are correct.

    D)  1 and 3 are correct.

    Correct Answer: C

    Solution :

                     According to Le-Chatelie?s principle, any change in concentration, pressure and temperature shifts the reaction in a direction which undo the effect of change. The reaction, \[{{C}_{2}}{{H}_{4}}(g)+{{H}_{2}}(g){{C}_{2}}{{H}_{6}}(g);\]    \[\Delta H=-32.7\text{ }kcal\] Is exothermic, therefore increase in temperature shifts the reaction in backward direction (ie, more\[{{C}_{2}}{{H}_{4}}\]is formed). Number of moles are more at left hand side, therefore decrease in pressure shifts the reaction in backward direction. If some\[{{H}_{2}}\]is removed, then to compensate it, reaction shifts in backward direction


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