JEE Main & Advanced Sample Paper JEE Main - Mock Test - 13

  • question_answer
    An ideal gas has a specific heat at constant pressure\[{{C}_{P}}=\frac{5R}{2}\]. The gas is kept in a closed vessel of volume \[0.0083\text{ }{{m}^{3}},\] at a temperature of \[300\text{ }K\]and a pressure of\[1.6\times {{10}^{6}}N/{{m}^{2}}\]. An amount of \[2.49\times {{10}^{4}}\] Joules of heat energy is supplied to the gas. Calculate the final pressure of the gas

    A) \[1.6\times {{10}^{5}}N{{m}^{-2}}\]       

    B) \[1.8\times {{10}^{6}}N{{m}^{-2}}\]

    C) \[3.6\times {{10}^{6}}N{{m}^{-2}}\]      

    D)  \[8.1\times {{10}^{3}}N{{m}^{-2}}\]

    Correct Answer: C

    Solution :

    We know that \[PV=nRT\]
    \[\therefore \,\,n=\frac{PV}{RT}=\frac{1.6\times {{10}^{6}}\times 0.0083}{8.3\times 300}=\frac{16}{3}=5.33\,moles\] \[{{C}_{P}}=\frac{5R}{2}\Rightarrow {{C}_{V}}=\frac{3R}{2}\]
    When \[2.49\times {{10}^{4}}J\] of heat energy is supplied at constant volume then we can use the following relationship to find change in temperature.
    \[Q=n{{C}_{V}}\Delta T\]
    \[\therefore \,\,\,\Delta T=\frac{Q}{n{{C}_{V}}}=\frac{2.49\times {{10}^{4}}}{5.33\times \frac{3}{2}\times 8.3}=375K\]
    Therefore, the final temperature
    \[=300+375=675K\]
    Applying Gay Lussac's Law, to find pressure.
    \[\frac{{{P}_{1}}}{{{T}_{1}}}=\frac{{{P}_{2}}}{{{T}_{2}}}\]
    \[\Rightarrow \,\,\,{{P}_{2}}=\frac{{{P}_{1}}{{T}_{2}}}{{{T}_{1}}}=\frac{1.6\times {{10}^{6}}\times 675}{300}=3.6\times {{10}^{6}}N{{m}^{-2}}\]


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