# What does a chemical engineer *do* anyways?

I am writing this because the general public (or at least the readers of this blog) have little knowledge or even an inkling as to what a chemical engineer does at his or her job. As Arthur C. Clarke might say, it might as well be magic.

Basically, I’m an accountant.

Some readers might scoff at that statement. My engineering buddies back in undergrad years would often joke about how accounting is the refuge of weed-outs in a last-ditch effort to obtain a non-Charmin degree.

But nonetheless – I am an accountant. But what “accounting” do I do?

Chemical engineers have a variety of tasks related to the sizing of equipment (such as reactors and separations), researching and investigating new technologies, the management of plant operations, the design and analysis of control systems, and environmental compliance and protection. But in all of these tasks, the first two steps are the same:

1. Write the equations of mass, energy, and momentum balance, and if necessary, the equations of entropy and population balance.*

2. Solve these equations using pencil and paper for basic problems, or a computer for practical problems.

That’s a pretty good two-sentence summary of what a chemical engineer does. Each of these equations follows the same basic form:

rate of accumulation of X in a volume = (rate of X in) – (rate of X out) + (rate of X generated) – (rate of X consumed)

The analogy to accounting is obvious:

rate of accumulation of money in the company = rate money is made – rate money is spent

I am too lazy to write the LaTeX for these balance equations, since they are awfully large in their general form (and it would be obnoxiously pedantic anyways). Googling will help the interested reader. The balance equations for mass and energy are the most important equations to solve. All other activities in chemical engineering, whether its making longer-lasting batteries, making condoms that don’t break as often, refining gasoline that burns cleaner, and building power plants that put out more juice, start with the writing and solution of these equations.

The take home message is this:

The first shovel of earth cannot be dug for the project without, at the bare minimum, having a complete mass and energy balance for the entire plant, from the raw feed input, the final finished products being wheeled out the door.

*For processes that involve discrete particles (such as crystals, pharmaceuticals, and powders), population balances are also needed. Entropy balances are useful for investigating the feasibility of a process, e.g. “under the best-possible circumstances thermodynamics will allow, is the system still possible to build and function as described?”