Question

if the heat enter to a system is 400 joule , find increase in its internal energy if the work done is 100 joule

Answer 1

Task. If the heat enter to a system is 400 joule, find increase in its internal energy if the work done is 100 joule.

Solution. By the first law of thermodynamics the change $\Delta U$ of internal energy of the system is equal to the difference of the heat $\Delta Q$ added to the system and work $\Delta W$ done by the system:

$\Delta U=\Delta Q-\Delta W.$

In our case

$\Delta Q=400\ joule,$

and

$\Delta W=100\ joule,$

whence the internal energy increases by

$\Delta U=\Delta Q-\Delta W=400-100=300\ joule.$