MCQ
The entropy change when $2\, moles$ of ideal monoatomic gas is heated from $200\,^oC$ to $300\,^oC$ and isochorically
  • A
    $\frac{3}{2}R\,\ln \left( {\frac{{300}}{{200}}} \right)$
  • B
    $\frac{5}{2}R\,\ln \left( {\frac{{573}}{{273}}} \right)$
  • $3R\,\ln \left( {\frac{{573}}{{473}}} \right)$
  • D
    $\frac{3}{2}R\,\ln \left( {\frac{{573}}{{473}}} \right)$

Answer

Correct option: C.
$3R\,\ln \left( {\frac{{573}}{{473}}} \right)$
c
Solution:- (C) $3 R \ln \left(\frac{573}{473}\right)$

As we know that, $\Delta S = nC _{ V } \ln \frac{ T _{2}}{ T _{1}}+ nR \ln V _{2} V _{1}$

$\because$ The process is isochoric, i.e., volume is constant.

$\therefore \Delta S = nC _{ V } \ln \frac{ T _{2}}{ T _{1}}$

Given:-

$n =2 moles$

$C _{ P }=\frac{3}{2} R [\because$ the gas is monoatomic $]$

$T _{2}=200^{\circ} C =(200+273) K =473 K$

$T _{1}=300^{\circ} C =(300+273) K =573 K$

$\therefore \Delta S =2 \times \frac{3}{2} R \times \ln \left(\frac{573}{473}\right)$

$\Rightarrow \Delta S =3 R \ln \left(\frac{573}{473}\right)$

Hence the change in entropy of the gas is $3 R \ln \left(\frac{573}{473}\right)$

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