Flash evaporation (FE) is a process widely used in industry to separate volatile compounds from a mixture. The analysis of this process is of great importance due to its rapid nature and variable thermodynamic properties. However, liquid-vapor equilibrium calculations with equations of state consume a large amount of time in numerical simulations. For this reason, in this work a software is presented to solve the Rachford-Rice equation, using McWilliams correlation and Newton Raphson method. Up to 5 compounds were considered to perform the simulation. Three case studies were proposed with the most used specific variables, such as temperature, pressure, molar composition and vapor fraction. The results obtained were compared with the process simulation software ASPEN version 12. In all cases, the results were similar to those of the commercial software.