BCECE Engineering BCECE Engineering Solved Paper-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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