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BCECE Medical BCECE Medical Solved Papers-2003

  • question_answer
    Equilibrium constant K , for the reaction, \[2HI(g){{H}_{2}}(g)+{{I}_{2}}(g)\]at room temperature is 2.85 and that at 698 K is \[1.4\times {{10}^{-2}}\]. This implies that the forward reaction is:

    A)  exothermic     

    B)  endothermic

    C)  exergonic      

    D)  unpredictable

    Correct Answer: A

    Solution :

    Key Idea: Write expression for equilibrium, constant and apply Le-Chateliers principle                 \[2HI{{H}_{2}}(g)+{{I}_{2}}(g)\]                 \[k=\frac{[{{H}_{2}}]\,[{{I}_{2}}]}{{{[HI]}^{2}}}\] When temperature increases, \[{{K}_{c}}\] decreases. \[\therefore \] Concentration of product decreases. It means forward reaction is not favoured at - higher temperature. This is true for exothermic reactions. So, the forward reaction is exothermic.


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