1. Problem Statement: For the regular solution model, develop the equations for the compositions of the coexisting phases in a binary system and plot the phase boundary as a function of χ/RT. 2. This question stems from Sandler's Introduction to Applied Statistical Thermodynamics. 3. The attempt at a solution I am having trouble understanding how to approach this problem. I know that the equations I need to develop are a function of x1, x2 -> (1-x1). I do not know where to start when considering an equation for a phase boundary. Any help would be appreciated.