Change in Enthelpy when Internal Energy does not Change

In summary, the change in enthalpy for a perfect gas undergoing isothermal expansion is 0, as the internal energy (U) does not change. The equation for enthalpy (H) is H=U+PV, but since U does not change, only Δ(PV) is left. However, since PV does not change during isothermal expansion, the final result is still 0.
  • #1
Luscinia
17
0

Homework Statement



The internal energy of a perfect gas does not change when the gas undergoes isothermal expansion. What is the change in enthalpy?

Homework Equations


H=U+PV


The Attempt at a Solution


The answer is 0

Since U, the internal energy, doesn't change, I assumed that the equation would be ΔH=PΔV. Why would PΔV equal 0 if there is an expansion (ΔV is not 0)? I'm guessing that I'm not seeing something here since this seemed to be a rather simple question.
 
Physics news on Phys.org
  • #2
The enthalpy is actually [itex]\Delta H = \Delta U + \Delta (PV)[/itex]. I don't think that PV will change.
 

FAQ: Change in Enthelpy when Internal Energy does not Change

1. What is meant by "Change in Enthalpy when Internal Energy does not Change?"

When the internal energy of a system remains constant, any change in enthalpy is solely due to a change in pressure or volume. This means that there is no change in the amount of energy within the system, but the distribution of energy may shift.

2. How is enthalpy different from internal energy?

Enthalpy is a measurement of the total energy of a system, including both its internal energy and the energy required to create a change in volume or pressure. Internal energy, on the other hand, only measures the energy contained within the system.

3. Can enthalpy change without a change in internal energy?

Yes, enthalpy can change without a change in internal energy if there is a change in pressure or volume. This is because enthalpy takes into account the energy required for such changes.

4. What is an example of a process where enthalpy changes but internal energy does not?

A common example is the melting of ice. When ice melts, the internal energy of the water and ice remain the same, but the enthalpy increases due to the energy required to break the bonds between the water molecules.

5. How is the change in enthalpy calculated when internal energy does not change?

The change in enthalpy can be calculated using the formula ΔH = ΔU + PΔV, where ΔH is the change in enthalpy, ΔU is the change in internal energy, P is the pressure, and ΔV is the change in volume. When ΔU is equal to 0, the change in enthalpy is solely determined by the change in pressure and volume.

Similar threads

Calculation of the change in internal energy of water
Replies
19
Views
4K
Change in internal energy during vapourization of water
Replies
1
Views
4K
Chemistry What does the differential of U mean in an irreversible process?
Replies
11
Views
392
Internal Energy Change: Homework Solutions
Replies
1
Views
2K
Work done by Octane Combustion Engine
Replies
2
Views
2K
Is enthalpy just the sum of internal energy and work against external pressure?
Replies
5
Views
654
Chemistry Calculation of thermodynamic variables for irreversible adiabatic process of ideal gas
Replies
9
Views
537
Chemistry How to understand the energy involved in mass transfer into an open system?
Replies
0
Views
211
Heat, Work, Change in Entropy and Energy
Replies
5
Views
3K
Internal Energy Changes in Various Systems
Replies
5
Views
4K

Hot Threads

Recent Insights

Back
Top