Question

A closed 2.0-l container holds 3.0 mol of an ideal gas. if 200 j of heat is added, what is the change in internal energy of the system?

Answer 1

The first law of thermodynamics states that:

`\Delta U = Q-W`
where

`\Delta U` is the variation of internal energy of the gas
Q is the heat absorbed by the gas
W is the work done by the gas

The container has a fixed volume, so there is no work done on/by the gas (because the work is proportional to the variation of volume:
`W=p \Delta V`). Therefore, W=0, and the equation becomes

`\Delta U = Q`
and the variation of internal energy of the gas is simply equal to the heat added to it:

`\Delta U = Q = +200 J`