In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas release `20 J` of heat and `8 J` of work is done on the gas. If initial internal energy of the gas was `30 J`, what will be the final internal energy?

Options

A. `42 J`
B. `12 J`
C. `10 J`
D. `18 J`

Answer

D

Explanation

We know `DeltaQ = DeltaU +DeltaW`. Since heat is released the system, `DeltaQ = -20J`
As work is done on the gas, `Delta W = -8J`
`:. -20J = DeltaU - 8W`
`DeltaU =-12J or U_(f) - U_(i) =-12J`
or `U_(f)=U_i-12=30-12=18J`.