There is gas under the piston. The gas is supplied with an amount of heat equal to 5 kJ.

There is gas under the piston. The gas is supplied with an amount of heat equal to 5 kJ. At the same time, he performs work equal to 12 J. Determine the change in the internal energy of the sestema. Is the internal energy of the system increasing or decreasing?

The change in the internal energy of the system ΔU is the sum of the amount of heat Q = 5 kJ = 5000 J reported to the system and the energy transferred in the process of performing work A on the system, that is: ΔU = A + Q. In our case, under the piston there is a gas that itself performs work equal to 12 J, that is, it loses energy and then A = – 12 J. Let us determine the total change in the internal energy of the system: ΔU = 5000 J – 12 J = 4988 J. Since ΔU> 0, the internal energy of the system increases.
Answer: the change in the internal energy of the system is ΔU = 4988 J, the internal energy of the system has increased.