A gas is allowed to expand in a well insulated container against a constant external pressure of 2 atm from an initial volume of 4.25 L to a final volume of 6.25 L. The change in internal energy (ΔU) of the gas will be:
A
– 675 J
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B
+ 675 J
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C
405.2 J
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D
– 405.2 J
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Solution
The correct option is D – 405.2 J w=−PextΔV=−2(6.25−4.25) =−4Latm =−4×101.3J[∵1Latm=101.3J] =−405.2J
From first law of thermodynamics, ΔU=q+w q=0 for adiabatic process ΔU=w=−405.2J