There have been some discussions here as to what type of processes create entropy rather than just move it around. It is established that a gradient of temperature can create entropy. However, the issue moved to partial pressure, and then even away from that. The previous discussion seemed to revolve around nonequilibrium thermodynamics. For clarity, I thought it would be useful to discuss the entropy creation one gradient at a time. This post presents problems with regards to the gradient of fugacity. 1) Can a nonzero gradient of fugacity create entropy? 2) Are there any conditions where a nonzero gradient of fugacity can't create entropy? 3) What does the adjective "quasistatic" mean with respect to the gradient of fugacity? Here is a link where fugacity is defined. http://en.wikipedia.org/wiki/Fugacity "Fugacity In chemical thermodynamics, the fugacity ( ) of a real gas is an effective pressure which replaces the true mechanical pressure in accurate chemical equilibrium calculations. It is equal to the pressure of an ideal gas which has the same chemical potential as the real gas. For example, nitrogen gas (N2) at 0°C and a pressure of 100 atm has a fugacity of 97.03 atm. This means that the chemical potential of real nitrogen at a pressure of 100 atm is less than if nitrogen were an ideal gas; the value of the chemical potential is that which nitrogen as an ideal gas would have at a pressure of 97.03 atm.” I think that the concept of fugacity is also used with respect to phases that aren't gases. I don't swear to it, but I think the formal definition is quite general with respect to phase. However, the definition in this Wiki article is general enough to start the discussion.