The complicated interaction between physically distinct, separable sections of matter termed phases that are in contact with each other is described by phase behavior. Solids, liquids, and vapors are the most common phases. In many petroleum applications, phase behavior is critical. Thermodynamics is the study of energy and its changes, which is crucial to understanding phase behavior. We can follow the energy changes that occur during phase transitions and anticipate the result of a process using thermodynamics. The goal of phase-equilibrium thermodynamics is to find properties like temperature, pressure, and phase compositions that emerge once all potential for further change has disappeared.