Final answer:
The work done by a system will cause a decrease in the internal energy, assuming no heat is transferred to or from the system.
Step-by-step explanation:
The first law of thermodynamics states that the change in internal energy of a closed system equals the net heat transfer into the system minus the net work done by the system. In equation form, the first law of thermodynamics is AU = Q-W.
If heat is added to the system, it increases the internal energy and a positive value of Q is used. On the other hand, if heat is removed from the system, it decreases the internal energy and a negative value of Q is used.
Therefore, the work done by a system will cause a decrease in the internal energy assuming no heat is transferred to or from the system.