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A gas expands isothermally against a con...

A gas expands isothermally against a constant external pressure of 1 atm from a volume of 10 `dm^(3)` to a volume of 20 `dm^(3)`. It absorbs 800 J of thermal energy from its surroundings. The `Delta`U is

A

`-312` J

B

`+123 J`

C

`-213` J

D

`+231 J`

Text Solution

Verified by Experts

The correct Answer is:
C
`W_("icr") =-P_("ext") (V_(2)-V_(1))`
`W=-1(20-10) = -10 dm^(3) atm = -10 dm^(3) xx (8.314 JK^(-1) mol^(-1))/(0.0821 dm^(3) K^(-1) mol^(-1)) = -1013 J`
From 1st w of thermodynamics `DeltaU = q+W = 800 J+(-1013 J) = -213` J
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