Where can we apply the first law of thermodynamics?

by kulkajinkya
Tags: thermodynamics
kulkajinkya is offline
Apr22-13, 12:55 AM
P: 12
Hi people, I have a question. Where can we apply the first law of thermodynamics? I mean is it applicable between 2 equilibrium points? Or between a reversible process?
When we consider free expansion of a gas into vacuum, we apply the first law. But since the process isn't reversible (or even defined), we apply it between the final and initial equilibrium points and hence conclude ΔU=0.
So my question is is it applicable between 2 equilibrium points, for a reversible process, or for a general irreversible/reversible process?
Phys.Org News Partner Physics news on Phys.org
A 'quantum leap' in encryption technology
Using antineutrinos to monitor nuclear reactors
Bake your own droplet lens
DrClaude is offline
Apr22-13, 07:38 AM
Sci Advisor
PF Gold
DrClaude's Avatar
P: 1,114
The first law of thermodynamics is just a particular formulation of the conservation of energy. Therefore, it applies at all times. It's just that separating energy into work and heat, which you do in thermodynamics, can be difficult for transient processes. When studying equilibrium thermodynamics, it is more common to apply it at the different points where the system is in equilibrium.

Register to reply

Related Discussions
Does the first law of thermodynamics apply to the cosmological universe? Classical Physics 1
Physical Chemistry books (Thermodynamics/Statistical Thermodynamics/Kinetics/QM) Science & Math Textbook Listings 1
Grad School: Apply now & defer, or apply later? Academic Guidance 4
How the first two laws of thermodynamics apply to order General Physics 5
Prof teaches Statistical thermodynamics in a Classical Thermodynamics class Academic Guidance 10