Question

A system does 125 J of work and cools down by releasing 438 J of heat. The change in internal energy is ____________ J.

Answer 1

Given that,

Work done by the system = 125 J

Energy released when it cools down = 438 J

To find,

The change in internal energy.

Solution,

As heat is released by the system, Q = -438 J

Work done by the system, W = -125 J

Using the first law of thermodynamics. The change in internal energy is given by :

$\Delta U=Q-W\\\\=-438-125\\\\=-563\ J$

So, the change in internal energy is 563 J.