An office room contains about 2000 moles of air . The change in the internal energy of this much air when it is cooled from `34 ^@ C ` to `24^@C` at constant pressure of 1.0 atm is
[ Use ` gamm _(" air") = 1.4 ` and universal gas constant `=8.314 J // mol -K]`

Options

A. `-1.9 times 10^5 J`
B. `+1.9 times 10^5 J`
C. `-4.2 times 10^5 J`
D. `+0.7 times 10^5 J`

Answer

C

Explanation

Answer(3) change in internal energy, `U = nC_vdT`
= n. `R/gamma -1 (T_2 -T_1)`.
= `2000 xx 8.314/1.4 -1 (-10)` .
= `-4.15 xx 10^5J` .
`therefore U cong -4.2 xx 10^5J`.