Why Chemistry Is the Subject Where Prior Knowledge Does the Most Damage

In most subjects, prior knowledge helps.

A student who has read widely comes to history class with context. A student who has grown up speaking a language comes to linguistics class with intuitions. Prior exposure to ideas, even informal and imprecise exposure, gives new learning somewhere to attach.

Chemistry is different. In chemistry, prior knowledge — the everyday, informal, common-sense understanding of the physical world that students have been building their entire lives — is one of the primary obstacles to learning.

Not because students are wrong to have it. Because it is coherent, internally consistent, deeply embedded, and wrong in exactly the ways that matter most for understanding chemistry.

The problem with everyday chemical intuition

Students arrive in chemistry class having already formed models of how substances work. These models were built from experience — from mixing things in kitchens, from reading warning labels, from absorbing cultural narratives about science — and they function well enough for navigating everyday life.

The problem is that chemistry, at the level where it becomes interesting and useful, operates differently from the world those models describe.

Everyday experience teaches that strong means intense. A strong smell, a strong flavor, a strong feeling — all of these are more of the thing in question. Students carry this directly into chemistry and read strong acid as meaning very acidic, with a correspondingly low pH. This is not always true. Strong refers to dissociation, not intensity. A dilute strong acid can be less acidic than a concentrated weak acid. The everyday model produces errors on almost every question that requires distinguishing strength from concentration.

Everyday experience teaches that equilibrium means balance, and balance means stillness. A balanced scale is motionless. An equilibrium between two things means neither is winning. Students apply this to chemical equilibrium and picture a system that has stopped — reactants and products sitting in fixed quantities with nothing happening. The dynamic model — both reactions ongoing, rates matched — is not just new information. It directly contradicts the picture students already have.

Everyday experience teaches that chemicals are dangerous and that natural substances are safe. Students who have absorbed this narrative approach chemistry with a framework that has no relationship to how substances actually behave. Concentration, context, and mechanism determine toxicity, not the origin or name of a substance. But the framework arrived before the chemistry class did, and it will resist correction long after the unit ends.

Why this is worse in chemistry than other sciences

Every science has to contend with prior models. Students come to physics with intuitions about motion that Aristotle shared and Newton corrected. They come to biology with essentialist intuitions about species that Darwin spent his career dismantling.

Chemistry is particularly vulnerable for two reasons.

The first is that chemistry language overlaps heavily with everyday language. Strong, weak, pure, natural, organic, acid, base, salt — all of these words exist in both ordinary English and chemical English with different meanings. In physics, the technical vocabulary is more distinctive. Force, acceleration, and momentum have everyday meanings, but they are also clearly technical terms. In chemistry, students routinely believe they understand a word when they have only encountered its everyday version.

The second is that the everyday models are often partially correct. Acids are generally corrosive in concentrated form. Strong acids do tend to have lower pH than weak acids at comparable concentrations. Equilibrium does involve a kind of stability. The partial correctness of the everyday model makes it harder to displace — students can generate correct answers in familiar contexts and never discover that their underlying model is wrong.

The misconceptions that persist longest

Research on chemistry misconceptions consistently identifies the same clusters — not because students are unusually resistant, but because these particular everyday models are especially robust.

The particle model of matter is one. Students understand, in a general sense, that substances are made of particles. They do not intuitively understand that those particles are in constant motion, that the space between them is genuinely empty, that dissolving does not destroy particles but separates them. The static particle model — particles as tiny, stationary chunks of substance — produces errors in anything involving phase changes, dissolving, or reaction mechanisms.

The substance model of chemical change is another. Students tend to think of chemical reactions as substances acquiring new properties, rather than as old bonds breaking and new bonds forming. The atoms are continuous with what they were before; only their arrangement changes. This is genuinely hard to grasp because it contradicts the appearance of reactions — wood that burns seems to disappear, not rearrange. The everyday model of destruction-and-creation is wrong in ways that undermine understanding of conservation, stoichiometry, and reaction mechanisms.

The energy model is a third. Students have a strong intuitive model of heat as a substance — something that flows into and out of objects, a kind of fluid that makes things hotter when it accumulates. The thermodynamic model — energy as a property of particle motion, transferred through collisions — is alien to everyday experience and resists the heat-as-fluid intuition even after explicit correction.

What this means for teaching

The implication is not that prior knowledge should be ignored. It is that it cannot be overwritten simply by presenting correct information.

A student who has the strong-means-intense model does not abandon it when the teacher says “strong refers to dissociation.” The correct definition sits alongside the incorrect model, waiting to be applied when the context makes it obvious and ignored when the context is ambiguous. The incorrect model remains available and will be selected under pressure — in an exam, in a novel problem, in any situation where the student cannot recall which rule applies.

Dislodging a prior model requires something the correct definition alone cannot provide: a direct confrontation between the model and a case it cannot explain. Show the student a concentrated weak acid with a lower pH than a dilute strong acid. The everyday model predicts the wrong answer. The student notices. The gap between the model and the observation creates the need for a better model — and the better model, when it arrives, has somewhere to land.

This is the sequence that works: surface the prior model, create a situation it cannot handle, build the replacement from there. It is slower than presenting the correct information directly. It produces understanding that the faster sequence does not.

The specific challenge for out-of-field teachers

Out-of-field chemistry teachers often share their students’ prior models.

Not because they are less intelligent or less prepared than specialist teachers. Because they learned chemistry the same way their students did — through definitions presented without the confrontations that would have displaced the everyday model underneath. The performance of understanding was adequate for assessment purposes. The underlying model was never replaced.

This matters because a teacher who holds the same prior model as their students cannot see it operating in student responses. The errors look like carelessness or failure to study rather than evidence of a specific wrong model. The correction addresses the surface without touching the structure.

Building the correct model — not just the correct information — before teaching a unit is the preparation that changes this. It is also the preparation that most teacher training does not provide, because most teacher training treats content knowledge as a matter of correct facts rather than coherent models.

If you want to know which prior models in chemistry you’re most likely to be working with — in yourself and in your students — the **free self-check is a useful diagnostic. And if the units where prior knowledge does the most damage — stoichiometry, equilibrium, acids and bases — are the ones you’re currently planning, the Survival Guides** are built around identifying and replacing the models that standard instruction leaves in place.

The students who are hardest to teach

The students who resist chemistry most strongly are often not the ones with the weakest prior knowledge. They are the ones with the most coherent prior model — a model that has served them well, that has been reinforced consistently, and that they have no particular reason to doubt.

The student who “just doesn’t get chemistry” is frequently a student whose prior model is so consistent and so deeply embedded that the correct model cannot find purchase. Every new concept is interpreted through the old lens. Every correct answer learned is a surface pattern that leaves the underlying model intact.

These students are not beyond reach. They require the one thing the textbook sequence almost never provides: a direct and honest confrontation between what they already believe and what they are being asked to believe instead.

That confrontation is uncomfortable. It is also the only thing that works.

I write for out-of-field chemistry teachers navigating content they didn’t study. Follow for more. Not sure where your gaps are? The **free self-check **takes five minutes.