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Question
A gas expands isothermally against a constant external pressure of 1 atm from a volume of 10 dm3 to a volume of 20 dm3. It absorbs 300 J of thermal energy from its surrounding. The △U is:
A gas expands isothermally against a constant external pressure of 1 atm from a volume of 10 dm3 to a volume of 20 dm3. It absorbs 300 J of thermal energy from its surrounding. The △U is:
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Solution
The correct option is C −213 J
In general, W=−∫V2V1PdV=−P(V2−V1)
W=−(1 atm)(20−10)=−10 dm3 atm.
=−1atm×10 dm3×8.314 J/K/mol0.08206 dm3−atm/K/mol=−1013 J
According to 1st law of thermodynamics,
△U=q+W=800 J+(−1013 J)=−213 J
Hence, option C is correct.
In general,
W=−∫V2V1PdV=−P(V2−V1)
W=−(1 atm)(20−10)=−10 dm3 atm.
W=−(1 atm)(20−10)=−10 dm3 atm.
=−1atm×10 dm3×8.314 J/K/mol0.08206 dm3−atm/K/mol=−1013 J
According to 1st law of thermodynamics,
△U=q+W=800 J+(−1013 J)=−213 J
Hence, option C is correct.
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