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As insulated container is divided into two equal portions. One portion contains an ideal gas at pressure \mathrm{P} and temperature \mathrm{T}, while the other portion is a perfect vacuum. If a hole is opened between the two portions, The change in internal energy is :
 

Option: 1

Less than zero


 


Option: 2

Equal to zero
 


Option: 3

More than zero
 


Option: 4

All of the above


Answers (1)

best_answer

As the system is thermally insulated,

\mathrm{ \Delta Q=0 }

Further as here the gas is expanding against vacuum (surroundings), the process is called free expansion and for it,

\mathrm{ \left.\Delta W=\int P d V=0 \quad \text { [as for vacuum } \mathrm{P}=0\right] }

So in accordance with first law of thermodynamics, i.e. \mathrm{\Delta Q=\Delta U+\Delta W},we

have \mathrm{ 0=\Delta U+0 \text {, i.e. } \Delta U=0 \text { or } U=\text { constant } }

So in this problem internal energy of the gas remains constant, i.e. \mathrm{ \Delta U=0 }. Now as for an ideal gas

\mathrm{ U=\frac{3}{2} \mu R T, \quad \text { i.e. } U \propto T }

So temperature of the gas will also remain constant, i.e. \mathrm{ \Delta T=0. }

Posted by

Irshad Anwar

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