In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out 30 J of heat and 10 J of work is done on the gas. If the initial internal energy of the gas was 40 J, then the final internal energy will be:

Question

In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out 30 J of heat and 10 J of work is done on the gas. If the initial internal energy of the gas was 40 J, then the final internal energy will be: (A) 30 J (B) 20 J (C) 60 J (D) 40 J

Tardigrade Admin · Accepted Answer

Energy remains conserved in the process according to first law of thermodynamics.
If an amount of heat

Q

is given to a system, a part of it is used in increasing the internal energy

(Δ U)

of the system and the rest in doing work

(W)

by the system.
Hence, we have

Q = Δ U + W

(first law of thermodynamics)
Given,

Q = - 30 J, W = - 10 J

∴ Δ U = - 30 + 10 = - 20 J

\Rightarrow U_{f} = - U_{i} = - 20 J

\Rightarrow U_{f} - 40 = - 20

\Rightarrow U_{f} = 40 - 20 = 20 J

Q. In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out 30J of heat and 10J of work is done on the gas. If the initial internal energy of the gas was 40J, then the final internal energy will be:

30 J

20 J

60 J

40 J

Q. In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out $30 J$ of heat and $10 J$ of work is done on the gas. If the initial internal energy of the gas was $40 J$ , then the final internal energy will be: