Question

An office room contains about 4000 moles of air. The change in the internal energy of this much air when it is cooled from 34° C to 19° C at a constant pressure of 1.0 atm is (Use `gamma_"air"` = 1.4 and Universal gas constant = 8.314 J / mol K) ____________.

Options

• -1.25 x 10⁶ J

• +1.25 x 10⁶ J

• -4.2 x 10⁵ J

• +4.2 x 10⁵ J

Answer 1

An office room contains about 4000 moles of air. The change in the internal energy of this much air when it is cooled from 34° C to 19° C at a constant pressure of 1.0 atm is -1.25 x 10⁶ J.

Explanation:

`"dU" = "n" xx "C"_"v" xx "d" theta`

`= "n" xx "R"/(gamma -1) xx "d" theta      ......(because  "C"_"v" = "R"/(gamma - 1))`

`= 4000 xx 8.314/0.4 xx (-15)`

`= 1.25 xx 10^6  "J"`