# Mechanical Engineering - Thermodynamics - Discussion

Discussion Forum : Thermodynamics - Section 2 (Q.No. 19)

19.

The free expansion process is a constant enthalpy process.

Discussion:

13 comments Page 1 of 2.
Mayur B said:
3 years ago

For ideal gases, as we know, internal energy and enthalpy are a function of temperature only, so if internal energy U remains constant, temperature T also remains constant which means enthalpy also remains constant.

Tejveer sharma said:
3 years ago

Well known that in free expansion temperature remains constant so internal energy must be constant.

But on another hand, because enthalpy is a point function and in this by considering the only initial and final point. It follows Boyle's law( PV=C). It is already seen that internal energy U is constant and so (U+PV)=C, and hence enthalpy remains constant.

But on another hand, because enthalpy is a point function and in this by considering the only initial and final point. It follows Boyle's law( PV=C). It is already seen that internal energy U is constant and so (U+PV)=C, and hence enthalpy remains constant.

Ashutosh kumar said:
4 years ago

For an ideal gas, temp remains constant during the free expansion process and internal energy & enthalpy both are a function of temperature so it becomes zero.

But this is not true for real gases.

And in question nothing mention about gases.

So, option incorrect should be the answer.

But this is not true for real gases.

And in question nothing mention about gases.

So, option incorrect should be the answer.

Arunkumar said:
4 years ago

Enthalpy is a constant pressure & volume.

The free expansion process is an expanded in volume increase and pressure decrease.

So, constant enthalpy is correct.

The free expansion process is an expanded in volume increase and pressure decrease.

So, constant enthalpy is correct.

Akhila said:
4 years ago

The free expansion process is also called as constant internal energy process so the answer is false.

Sandeep said:
4 years ago

Initial and final enthalpy are same but we can not say this process is constant enthalpy process because during expansion enthalpy first increases then decreases.

Aditya loachab said:
5 years ago

Throttling process is also called isenthalpic process in which enthalpy remains constant before and after throttling process so it's not a correct answer.

S Bera said:
6 years ago

In Free expansion process dQ=0,du=0,dw=0,enthalpy =0(const).

Hari said:
7 years ago

Free expansion process: Q = Delta U + W = 0.

Enthalpy: U + PV.

So, Internal energy is =0.

Enthalpy = PV.

Enthalpy: U + PV.

So, Internal energy is =0.

Enthalpy = PV.

Mohammed Riyas said:
7 years ago

Free expansion must be an irreversible non flow process. So internal energy should be constant.

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