Internal energy

[Stevin1H]

Can someone explain the concept behind when the change in internal energy would be equal to 0?

[Karishma_1G]

Delta U for an isothermal reversible expansion is zero. These types of reactions usually take place in a heat reservoir. The energy that is lost when the system does work is replaced by heat energy from the surroundings. Therefore q and w are equal in magnitude and opposite in sign; q is positive since heat is coming into the system and w is negative since work is being done by the system. So when you add q and w to get delta U, it is zero.

[CHEM 14B Lover]

"The energy lost as work is replaced by heat"; but you say these reactions normally happen in a heat bath? What if there isn't a heat bath? Would it simply not be isothermal reversible?