In chapter 3, we discussed two-film theory and the use of the overall mass transfer coefficients that will be one of our foundational components in solving practical mass transfer problems over the course of the semester. In your own words, explain what two-film theory is and how it simplifies real mass transfer across an interface? How does the overall mass transfer coefficient develop from two-film theory? Finally, what is the difference between the overall mass transfer coefficients based on the gas and liquid phase and why might we use one over the other?