In a thermodynamic process, pressure of a fixed mass of a gas is changed in such a manner that the gas releases 20 J of heat and 8 J of work is done on the gas. If the initial internal energy of the gas was 30 J, 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 releases 20 J of heat and 8 J of work is done on the gas. If the initial internal energy of the gas was 30 J, the final internal energy will be: (A) 18 J (B) 9 J (C) 4.5 J (D) 36 J

Tardigrade Admin · Accepted Answer

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

Q

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

(Δ U)

of the system and the rest in doing work

(W)

by the system,
hence

Q = Δ U + W

Heat released by system

Q = - 20 J

Work done on the gas

W = - 8 J

∴ Δ U = Q - W

= - 20 - (- 8) = - 12 J

Final internal energy

U_{f} = U_{i} + Δ U = 30 - 12 = 18 J

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

18 J

9 J

4.5 J

36 J

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