But Just What Is Fugacity?

If you understand fugacity, congratulations, but it seems to be one of the concepts the eludes many chemical engineering students, at least for a while. In the window at right, you'll find a fugacity tutorial that should help set you straight. And if this isn't enough, the video series Learn ChemE has several other tutorials covering different aspects of fugacity that might finally put your questions to rest. You can check out What Is Fugacity?, What Is Fugacity in a Mixture?, and Three-Component Solution Fugacities, or just check out this long list of all the fugacity tutorial titles for the one that suits you best. 

What other ChE concept took a while to stick?