The external environment received 1200 J of the amount of heat from the thermodynamic system and performed

The external environment received 1200 J of the amount of heat from the thermodynamic system and performed work on the system by 700 J. How has the internal energy of the system changed?

According to the first law of thermodynamics, the change in the internal energy of the system U is equal to the difference between the heat received Q and the work A by the perfect system. It turns out that you can write down the formula:

U = Q + A.

Consequently, since the external environment performed 700 J of work on the thermodynamic system, and received 1200 J, we write:

U = -1200 + 700 = – 500 J.

A negative sign indicates that the internal energy of the thermodynamic system has decreased.

Answer: the internal energy of the thermodynamic system has decreased by 500 J.