Chemical and Biomolecular Engineering

Official blog of the Lehigh University Chemical Engineers

ChE 031 — Material and Energy Balances

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ChE 31 textbookChE 31 is the typical first Chemical Engineering course taken by ChemE majors. As the title of textbook suggests, elementary principles of chemical processes/systems are the focus of the class. When learning anything, you first learn the basics to develop a foundation for more complex ideas, Chem Engineering is no different.

ChE 31 introduces the equation [Accumulation = Generation + Input – Consumption – Output] which is the basis for describing chemical systems. In essence, when mass enters a system it must then leave the system in the same quantity (Input=Output). By examining either molar or mass flow rates and their respective mass and mole fractions, you can determine all variables in a system. Similarly, we just started studying energy balances in systems. In this case, the potential and kinetic energy of the system must be considered, along with the change in enthalpy. Enthalpy is the total thermodynamic energy of a system (internal energy, etc.) Work done by/on the system and heat added/taken from the system must also be considered. As with mass balances, energy that enters a system must equal energy that leaves the system.

A “system” refers to a series pipes and tubes that connect different apparatuses together. These include evaporators, condensers, absorbers, and compressors among many other devices. Solids, liquids, and gases pass through the system and are altered by the different devices. A system always has a goal or function; two liquids may have to be separated, or a reaction may have to take place and then a byproduct may need to be purged from the system. The functional possibilities of a system are truly endless, and they are an imperative aspect of many industries. Oil refineries, plastic manufacturers, and pharmaceutical companies all use chemical processes to complete a task or make a product. The information and procedures taught in ChE 31 form a basis for understanding key aspects of chemical engineering. It is extremely interesting to learn about different processes and types of equipment, and how they are used in the real world. I look forward to applying the techniques and ideals from ChE 31 to later classes and in an eventual career.

Example of a System

Example of a System


Author: Ben Dunmire

I am a sophomore Chemical Engineering major at Lehigh. On campus, I am the president of Club Baseball and a member of AIChE and NSCS. Outside of school, I enjoy the outdoors, fishing, and any type of athletic activity. You can reach me at

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