A gas sample is cooled and loses 65 J of heat. The gas contracts as it cools and work done on the system equal to 20 J. What are q, w and △U ?
A
q=−65J,w=20J,△U=−45J
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B
q=65J,w=10J,△U=−35J
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C
q=−70J,w=10J,△U=35J
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D
q=65J,w=20J,△U=45J
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Solution
The correct option is Aq=−65J,w=20J,△U=−45J From first law of thermodynamics △U=q+w
where ΔU = change in internal energy of the system q = heat energy during the process w = work done during the process q=−65Jw=20J △U=−65+20=−45J