# Is Delta Enthalpy Zero for an Isothermal Gas Expansion Process?

• sachin123
In summary, delta enthalpy is not zero for exothermic or endothermic reactions. It can be zero when there is no change in energy during a reaction, indicating equilibrium or no reaction. Delta enthalpy is related to internal energy through the equation: delta H = delta U + P * delta V. Internal energy refers to the total energy of a system.
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.

sachin123 said:
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.

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.

## 1. Is delta enthalpy zero for an exothermic reaction?

No, delta enthalpy is not zero for an exothermic reaction. In an exothermic reaction, energy is released, resulting in a negative value for delta enthalpy.

## 2. Is delta enthalpy zero for an endothermic reaction?

No, delta enthalpy is not zero for an endothermic reaction. In an endothermic reaction, energy is absorbed, resulting in a positive value for delta enthalpy.

## 3. Can delta enthalpy ever be zero?

Yes, delta enthalpy can be zero in some cases. This occurs when there is no change in energy during a reaction, meaning that the reactants and products have the same enthalpy.

## 4. What does a delta enthalpy of zero indicate?

A delta enthalpy of zero indicates that there is no change in energy during a reaction. This could mean that the reaction is at equilibrium or that there is no reaction occurring.

## 5. How is delta enthalpy related to internal energy?

Delta enthalpy is related to internal energy through the equation: delta H = delta U + P * delta V. This equation takes into account changes in both internal energy and pressure-volume work. Internal energy refers to the total energy of a system, including both kinetic and potential energy.

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