An ideal gas is expanded from (p1,V1,T1) to (p2,V2,T2) under different conditions. The correct statement(s) among the following is/are:
A
The work done on the gas is maximum when it is compressed irreversibly from (p2,V2) to (p1,V1) against constant pressure p1
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B
The work done by the gas is less when it is expanded reversibly from V1 to V2 under adiabatic conditions as compared to that when expanded reversibly from V1 to V2 under isothermal conditions
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C
The change in internal energy of the gas is (i) zero, if it is expanded reversibly with T1=T2, and (ii) positive, if it is expanded reversibly under adiabatic conditions with T1≠T2
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D
If the expansion is carried out freely, it is simultaneously both isothermal as well as adiabatic
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Solution
The correct options are A The work done on the gas is maximum when it is compressed irreversibly from (p2,V2) to (p1,V1) against constant pressure p1 B The work done by the gas is less when it is expanded reversibly from V1 to V2 under adiabatic conditions as compared to that when expanded reversibly from V1 to V2 under isothermal conditions D If the expansion is carried out freely, it is simultaneously both isothermal as well as adiabatic Case of expanding thus →V2>V1 Work done in case of isothermal : Wrev=−nRTlnVfinalVIntial Wirr=−pExt(VFinal−VIntial)
Option -A: The work done on the gas is positive because the gas is compressed; the surroundings do positive work on the gas. Note that the work done on the gas is greater for the irreversible process
wirr > wrev
Option-B:|Wisotherm>Wadiabatic|
Option -C:
(I) zero T1=T2=tempconstant,i.e,△T=0 △E=nCv△T=0 (ii) postive T1≠T2 during adiabatic expansion internal energy decreases .