Is Delta Enthalpy Zero for an Isothermal Gas Expansion Process?

[sachin123]

Is delta enthalpy zero for...

Is delta H, for an isothermal process in which a gas expands?
delta H=delta U+work done,correct?
delta U is 0,but work done = nCln(V2/V1).
So,delta H is not equal to 0.But my book says so.

 

[Ygggdrasil]

delta H=delta U+work done,correct?
.

No. deltaH = deltaU + delta(PV). Work done is p delta(V) (under conditions of constant pressure).

For an ideal gas delta(PV) = R delta(nT). As long as the number of gas molecules in the system (n) and the temperature (T) remain constant, delta(PV) = 0.

 

[quicknote]

The answer to this question depends on the specific conditions of the process. In general, delta H (change in enthalpy) is not necessarily equal to 0 for an isothermal process in which a gas expands. This is because enthalpy includes not only the internal energy (delta U) but also the work done on or by the system (nCln(V2/V1)). Therefore, if the work done is not equal to 0, then delta H will also not be equal to 0.

However, if the process is reversible and occurs at constant pressure, then delta H will be equal to 0. This is because at constant pressure, the work done is equal to -PdeltaV, which in this case is equal to nRTln(V2/V1). Since delta U is also equal to nCv(T2-T1), and for an isothermal process T2=T1, delta H will be equal to 0.

It is important to note that the concept of enthalpy is only applicable to reversible processes, and it is possible that your book may be referring to a specific case where the process is reversible and occurs at constant pressure. Therefore, it is always important to consider the specific conditions and assumptions when discussing enthalpy or any other thermodynamic property.