Three Reflections from Three Basic Principles of Chemical Engineering

Chemical Engineering is often touted as one of the most difficult degree programs in which one could major. Luckily, as far as I know, nobody is expected to learn it unless they want to.

Designing a distillation tower for crude oil might not be the sexiest subject one would want to learn in this era of digital and green economy; but nevertheless, I have extracted *clears throat* three valuable basic principles from the heyday of booming oil-based economy. Worry not, for no mathematics prerequisite is needed.

1. Know your system, boundary, and surroundings
2. In every system there exists balance, equilibrium, and rate
3. All models are wrong, some models are useful

All the three principles above are interconnected and, while by itself is useful for philosophical inquiry, can also be utilized as a framework for practical real-life, non-engineering situations. In fact, I will prove it to you in the last section of this writing.

Reflection #1: Know your system, boundary, and surroundings

In every situation, physical or mental, we can always limit the scope of our interest for that situation. Things which are part of our interest become a group which is called system, while everything else becomes its surroundings. At the border between system and surrounding, we have an imaginary line which we conveniently name boundary.

Illustration of a system, closed by boundary, and encircled by surroundings (Source: Wikipedia)

System has a set of qualities or features which defines the system itself, we call them properties. The value of properties at boundary is called boundary conditions, which define the relationship between our system and its surroundings.

In choosing what comprises the system, there is no right or wrong answer. However, trade-off exists. If our system is too small or too big, defining the boundary conditions will be harder, or even impossible, so much that we cannot do anything about the system.

In life, we call our system as “things that we can control” and its surroundings as “things that we cannot control”. Any objective or measurement of interest can be our properties; we may take, for example, the resolution of the problem and our mental health.

If we decide that we are responsible for everything, we will have an unnecessarily large system. We might find it difficult to evaluate our properties in the boundary conditions since we have taken almost everything conceivable into our system, leaving the surroundings seemingly unrelated. As a result, we will never solve any problem right, or at the best case scenario we will be spending too much time or effort than expected.

Conversely, if we choose to take an overly limited scope of responsibility, our system becomes conveniently minuscule. It becomes very tempting to give up immediately, knowing that our problem will never be solved no matter what due to the apparently uncontrollable surroundings. At the end of the day, we might never get anything done, or at best, our impact is severely diminished.

Reflection #2: In every system there exists balance, equilibrium, and rate

While facing a situation, most people are only aware about its balance, which more or less says, “If our side gains something, the other side loses that thing.” Hence, we are familiar with the concept of zero-sum game.

At its very core, balance states that whatever going in subtracted by whatever going out equals to whatever stays inside. Therefore, if we can expand what are all the sources from which something goes in and what are the destinations to which it goes out, we might think we have the big picture figured out. Balance, however, is not the only universal rule.

Illustration of mass balance of slurry in a settling tank (Source: Wikipedia)

In short, equilibrium dictates the possibility of something to happen, while rate determines the feasibility of it. Something that is feasible must be possible, but the same cannot be said for the reverse. Walking from Mumbai to Madrid, for example, is possible but not feasible for a normal human.

Equilibrium and rate, however, are independent of each other. There is no causal relationship between the endurance of a normal human in walking and the distance separating Mumbai and Madrid. As a result, we need to evaluate both separately, although it might seem that it is counter-intuitive to do so naturally.

We tend to visualize both balance and equilibrium with this image, hence the confusion (Source: Wikipedia)

Balance is pretty much what it is, a set of static and unchangeable equations. It merely states the conservation of things, i.e. things do not just disappear out of nowhere. In contrast, both equilibrium and rate may adapt given different conditions or inherent characteristics.

Walking from Mumbai to Madrid will be impossible if there is a pandemic outbreak. It can be both possible and feasible if, say, things are back to normal and the persons participating are free of constraints and have a strong determination to do so; for example, they are financially extravagant, physically fit adults on indefinite sabbatical leave looking for a once-in-a-lifetime adventure.

Reflection #3: All models are wrong, some models are useful

This point is less exclusive to chemical engineers than the previous two as other professions such as statisticians and economists understand it just as well. In fact, it is a paraphrase of a quote by George Box, a British statistician.

From what time should we take the bus to reach a destination timely to how the stock market is going to look like next year, everyday we are expected to make a forecast, albeit some questions are easier than the other. What stands between a forecast and a random guess is a model.

We subconsciously create a model when deciding how to navigate the public transport (Source: https://www.transjakarta.co.id/peta-rute/)

I’m not going to write down the formal definition of a model here. All you need to know is how to do it. The next time you face a life problem, remember to identify your system, surroundings, and boundary then define its balance, equilibrium, and rate. Then, you already have a model, at least from a Chemical Engineering perspective.

Let us take an example of a common life situation, say, applying for jobs. Recall that the first thing to do is to limit what we can and cannot control.

System

• Which jobs I would apply for and when
• What preparations I take (certifications, seeking help from friends, etc.)
• Financial budgeting for the logistics of job-seeking
• How I dress for and how I behave in the interview
• How I handle rejections

Surroundings

• The overall condition of the economy, which sector is on hiring freeze and which on hiring spree
• Whether the company to which I apply responds positively
• The conduct of the interviewers
• Qualification of other applicants
• Consequence of past actions which I cannot do anything about, e.g. college, GPA, past credentials, etc.

Boundary

• Properties: success chance and self-esteem
• If I have prepared well and the job requirements suit my qualification, offer or rejection is like rolling a dice
• If my interview goes poorly although the interviewer does nothing wrong, I need more practice to improve my success chance in the future
• If I keep getting rejections, I need to improve my qualifications which are feasible and relevant to the jobs I want
• If I keep getting rejections although I have been doing well, I need to relax my criteria for jobs that I am willing to apply for

Now that we have identified our system, surroundings, and boundary; let us proceed to the next step: balance, equilibrium, and rate.

Balance

• The number of jobs I apply for, subtracted by the number of job applications get accepted or rejected, and the number of job applications I respond, equals to the number of job applications in progress

Equilibrium

• My chance of securing an offer decreases as the salary and prestige of the job increase because such job attracts more competitive applicants
• My chance of securing an offer increases as my qualification increases
• The more jobs I apply, the higher my chance to secure an offer is
• The more I network with relevant people, the higher my chance to secure an offer is
• I cannot accept more than one job offers within the same recruiting period

Rate

• How urgent is it for me to secure a job offer immediately? What is my maximum wait time?
• It is faster to apply for a job than to get a confirmation for acceptance or rejection. How long does it take, on average, for any given company to accept or reject my application?
• How often does a new job opening which suits my qualification and interest pop up?
• Is there anything I can do, which I can complete before my maximum waiting time, that will increase my chance for an offer?
• Considering the answers for questions above, how selective should I be in matter of choosing which jobs to apply for? How selective should I be in accepting or rejecting a job offer, should I get one?

This is an example of a useful model, which will help us to decide our approach in the whole job-seeking process, but nonetheless by itself is wrong. Looking at the balance, are you aware of what is being assumed?

Here, we assume that it is impossible to get a job offer out of nowhere without having applied for it. However, in life, such thing happens, despite not in most cases. If we are to include that in our model, though, how and where should we put that element of miracle? Next on, how does that affect our equilibrium and rate?

As a general rule of thumb, a more complex model is not necessarily a better model. In fact, in the majority of cases, the opposite is true. We should keep our model simple enough by including only conceivable and significant elements, to the point of neglecting the others. Are you familiar with the slogan Keep It Simple, Stupid ? It is a design principle employed by the U.S. Navy.

Too long, didn’t read

• In facing a problem, Chemical Engineering suggests us to limit our scope of interest (system) and to define the relationship (boundary) between what is inside and outside (surroundings) of it.
• Identify what are reasonably conserved (balance) in a situation, then list of all possible outcomes (equilibrium), and lastly, how fast those outcomes could happen, compared to the time frame of the situation (rate).
• In identifying the six things previously mentioned, include only simple, conceivable, significant elements, so that when something unexpected happens you know where that does not come from (Keep It Simple, Stupid).