WB JEE Medical WB JEE Medical Solved Paper-2009

  • question_answer
    Equal volumes of molar hydrochloric acid and sulphuric acid are neutralized by dilute NaOH solution and x kcal and y kcal of heat are liberated respectively. Which of the following is true?

    A)  \[x=y\]

    B)  \[x=\frac{y}{2}\]

    C)  \[~x=2y\]                          

    D)  None of these

    Correct Answer: B

    Solution :

                     Heat of neutralisation = Heat of formation of water (1 mol) \[HCl+NaOH\xrightarrow{{}}NaCl+{{H}_{2}}O;\] \[\Delta H=-x\] or \[\underset{1\,mol}{\mathop{{{H}^{+}}}}\,+\underset{1\,mol}{\mathop{O{{H}^{-}}}}\,\xrightarrow{{}}\underset{1\,mol}{\mathop{{{H}_{2}}O;}}\,\]          \[\Delta H=x\] \[{{H}_{2}}S{{O}_{4}}+2NaOH\to N{{a}_{2}}S{{O}_{4}}+2{{H}_{2}}O;\Delta H=-y\]or \[2{{H}^{+}}+2O{{H}^{-}}\xrightarrow{{}}2{{H}_{2}}O;\]                \[\Delta H=-y\] \[{{H}^{+}}+O{{H}^{-}}\xrightarrow{{}}{{H}_{2}}O;\]        \[\Delta H=-\frac{y}{2}\] \[\Rightarrow \]               \[\Delta H=\Delta H\] \[\therefore \]  \[x=\frac{y}{2}\]


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