NEET NEET SOLVED PAPER 2015 (Re)

  • question_answer
    4.0 g of a gas occupies 22.4 L at NTP. The specific heat capacity of the gas at constant volume is \[5.0J{{K}^{-1}}mo{{l}^{-1}}\]. If the speed of sound in this gas at NTP is 952 \[m{{s}^{-1}}\] then the heat capacity at constant pressure is (Take gas constant R = 8.3 \[J{{K}^{-1}}mo{{l}^{-1}}\])                

    A)  8.0 \[J{{K}^{-1}}mo{{l}^{-1}}\]                  

    B)  7.5 \[J{{K}^{-1}}mo{{l}^{-1}}\]

    C)         7.0 \[J{{K}^{-1}}mo{{l}^{-1}}\]  

    D)         8.5 \[J{{K}^{-1}}mo{{l}^{-1}}\]

    Correct Answer: A

    Solution :

    Given, \[M=4gm,V=22.4L,{{C}_{v}}=5J{{K}^{-1}}mo{{l}^{-1}}\] \[{{V}_{sound}}=952m/s,{{C}_{p}}=?\] As. velocity of sound, \[{{V}_{sound}}=\sqrt{\frac{\gamma PV}{My}}\] \[\Rightarrow \,\,\,\,\,\,\,\,\gamma =\frac{M}{pV}v_{sound}^{2}=\frac{{{C}_{p}}}{{{C}_{v}}}\] so heat capacity at constant pressure, \[{{C}_{p}}={{C}_{v}}\left[ \frac{M}{pV} \right]v_{sound}^{2}=5\left[ \frac{4\times {{10}^{-3}}}{{{10}^{5}}\times 22.4\times {{10}^{-3}}} \right]{{(952)}^{3}}\]\[=\frac{20}{22.4}\times {{(952)}^{2}}\times {{10}^{-5}}\] \[=809.200\times {{10}^{-5}}\,=8.09\,\,J/mol\,K\].


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