isothermal reactions

[Rhea Shah 2F]

Why is internal energy equal to 0 in an isothermal reaction?

[Jonathan Gong 2H]

To think about an isothermal reaction/process, you can refer to the equation PV = nRT. In an isothermal reaction, the values represented by P and V, respectively, will either increase or decrease so as to maintain constant temperature. So, if pressure decreases, volume increases, which allows temperature to stay constant and internal energy to equal 0. From another perspective, when the gas does expansion work where volume increases, pressure simultaneously decreases. Meaning, the system loses an amount of heat equal to the work of the gas. Ultimately, the heat and work cancel out, making change in internal energy 0.

[Jielena_Bragasin2G]

Internal energy is dependent on temperature; no change in temperature will lead to no change in internal energy.

[zfinn]

isothermal reactions mean there is no change in temperature, and therefore it can't have a change in internal energy

[Keya Jonnalagadda 1A]

Just to clarify - isothermal means there is no temperature. As others have said, internal energy is a state function, which depends on temperature. Thus, without a temperature change, even if you have isothermal expansion, compression, or pressure change, the internal energy will be 0. Delta U = q+w, so even if work is done in such a process, the q will be the exact opposite to match and make sure the internal energy is constant.

[Emil Velasco 1H]

For isothermal, there is no change in temperature therefore there is no change in internal energy

[sarahforman_Dis2I]

Why is internal energy equal to 0 in an isothermal reaction?

One way that a TA explained this concept to me, is the U is a function of T, meaning that if the temperature changes, then the internal energy must change as well (because the molecules will have more motion).

[Brian_Ho_2B]

Why is internal energy equal to 0 in an isothermal reaction?

To add on to what others have said, in an isothermal system such as the isothermal, reversible expansion, delta U equals zero, which may mean that either the system is isolated (eg a very insulated beaker) OR the work is equal to negative heat. In the isothermal reversible expansion, any and all heat applied to the system is ALL converted into work done for the reversible expansion, which is why temperature doesn’t change. None of the heat is used to raise the temperature in a perfect heating engine.

[lauraxie2e]

If temperature doesn't change, internal energy doesn't change.