"Why is chemistry so hard" is searched by students in the autumn of their first real chemistry course, by parents of a child who was fine in science until this year, and by college students in a required general chemistry course that is going badly. The honest answer is that chemistry is hard in five particular ways, that most students have two of them, and that each has a fix. Finding yours is the whole job.
The honest answer
Chemistry sits between physics and biology and borrows the difficulties of both. From physics it takes calculation and abstract models. From biology it takes a large body of facts and vocabulary. Then it adds a problem neither has: everything it describes happens at a scale you cannot see, so you must carry a picture of atoms and molecules in your head and reason from it, without ever being able to check the picture against anything.
Students who find chemistry easy are not usually cleverer. They have the picture. A reaction, to them, is particles rearranging; an equation is a sentence about that; a calculation is counting particles by weighing them. Students who find chemistry hard have symbols and rules instead of the picture, and symbols and rules are hard to remember, impossible to apply to a new situation, and feel arbitrary, because without the picture they are.
1. It is three subjects in one
Physical chemistry is mostly maths and models: moles, gases, energy, rates, equilibrium. Organic chemistry is patterns and mechanisms: a few families of molecules and how they react. Inorganic chemistry is a body of facts organised by the periodic table. They need different ways of thinking, and a student who is good at one is often lost in another, which is why "I am good at chemistry" and "I am bad at chemistry" are both usually half true.
What to do: find out which of the three is the problem; it is rarely all three. Then study it in its own way: physical chemistry by doing calculations, organic by drawing mechanisms until the patterns show, inorganic by the periodic table, learning trends down a group and across a period rather than facts one by one.
2. It happens at a scale you cannot see
In physics, you can watch the ball fall. In biology, you can look at the cell. In chemistry, the thing that is actually happening, particles colliding and rearranging, is invisible, and the student has to imagine it correctly and reason from the imagined picture. Most school chemistry is taught in symbols because symbols fit on a board, and the particle picture is left to be inferred. Many students never infer it.
What to do: draw particles. For every reaction, draw the before and after at the particle level: how many of each, what bonds broke, what formed. For every solution, draw what is floating in it. The questions that decide grades in AP, A-level and IB chemistry ask for exactly this, because the mark schemes credit explanation at the particle level and nothing else.
3. The maths arrives without warning
A chemistry course usually opens descriptively: atoms, the periodic table, bonding, with little calculation. Then the mole arrives, and with it ratios, unit conversions, rearranged formulas, and later logarithms for pH and equilibrium. Students who chose chemistry as the non-mathematical science are ambushed, and because the maths is inside a chemistry chapter, nobody tells them that their problem is maths.
What to do: name the maths. Chemistry needs ratio and proportion, rearranging a formula with three or four symbols, unit conversion, scientific notation, and later logarithms. Each is a week of separate practice. A student who is "bad at chemistry" from the mole onward is very often fine at chemistry and weak at ratios.
4. The vocabulary is enormous
Chemistry has more technical words than any other school science, and many of them are ordinary words with precise meanings that differ from the everyday ones: strong, weak, concentrated, dilute, saturated, reduce, oxidise, spontaneous. A question that says "a strong acid" means something specific, and a student who reads it in the everyday sense answers a different question. The vocabulary is also layered: you cannot understand "equilibrium constant" without "equilibrium", or "oxidising agent" without "oxidation", and the definitions pile up.
What to do: keep a definitions page per topic, in your own words, with one example each, and test yourself on it weekly, by recall rather than by rereading. The method that makes chemistry vocabulary stay is set out in active recall for chemistry. And read exam questions twice, underlining every technical word, before answering.
5. Everything depends on the mole
Chemistry is cumulative in a particular way. The mole, taught early, is the idea that lets you count particles by weighing them. Stoichiometry uses it. Concentration uses it. Gases, energy changes, rates, equilibrium, acids and bases, electrochemistry: every one of them uses it. A student who did not fully get the mole in the first term meets it again, disguised, in every later chapter, and each chapter feels mysterious for a reason that has nothing to do with that chapter.
What to do: go back to the mole, whatever year you are in. Three questions test it: how many moles are in 11 grams of carbon dioxide; what mass of water forms when 4 grams of hydrogen burns completely; what is the concentration when 5.85 grams of sodium chloride dissolves to make 500 millilitres of solution. (0.25 mol; 36 g; 0.2 mol per litre.) A student who can do all three without hesitation is ready for every later chapter; one who cannot should spend a week here before anything else.
Which reason is yours?
| If this sounds like you | The likely reason |
|---|---|
| "I was fine until the calculations started" | 3, and probably 5: the maths, and the mole |
| "I can do the calculations but cannot explain anything" | 2: no particle picture |
| "I understand it in class and forget it by the test" | 4: vocabulary learned by rereading instead of recall |
| "Organic makes sense and physical chemistry does not" (or the reverse) | 1: three subjects, and one of them is yours |
| "Every new chapter feels like it assumes something I never learned" | 5: the mole, almost certainly |
| "I know the facts and lose marks on the six-mark questions" | 2 and 4: the mark scheme wants particles and precise words |
| "I am just not a chemistry person" | Usually 2 and 3 together, with a label on top |
Most students find two rows. That is the whole problem, and it is smaller than "chemistry".
Chemistry at each level
| Level | What makes it hard there |
|---|---|
| Middle school and Class 9 to 10 | The first symbols and equations; balancing; the first mole calculations, where reason 5 begins |
| High school chemistry and IGCSE or GCSE | The mole in earnest; the six-mark explanation questions that want particles and the exact word |
| AP Chemistry | A college year in a school year; equilibrium and acids and bases, where reasons 2, 3 and 4 arrive together; the detail is in is AP Chemistry hard |
| A-level and IB | Volume: all three branches at depth; organic mechanisms; the practical and the internal assessment |
| CBSE Class 11 and 12 | The Class 11 jump, with the mole concept, atomic structure and equilibrium in the first months; the organic chapters of Class 12 |
| College general chemistry | Pace, and the assumption that the mole and the particle picture are already there |
Chemistry against physics and biology
Physics has fewer facts and more maths in every topic; chemistry has more facts and maths in particular units, so physics is harder to start and chemistry harder to finish. Biology has the most to remember and the least to calculate, and gives you something to picture for every idea, which is why students who found biology easy are often surprised by chemistry. The full comparison with physics, with a ten-question check that predicts which you will find harder, is in is physics harder than chemistry.
What to do this month
- Find the reason, from the table. Twenty minutes with a marked test: sort every lost mark into maths, explanation, vocabulary, or a topic that assumed something earlier.
- If it is the mole, a week there, with the three questions above as the test.
- If it is the picture, draw particles for every reaction and every solution for a fortnight.
- If it is the maths, ten minutes a day of ratios, rearranging and unit conversion, separate from chemistry.
- If it is vocabulary, a definitions page per topic and a weekly recall test.
- Then twenty minutes a day of questions from past papers, with the mark scheme beside you, so that you learn what an answer has to contain.
Where to get help
A 1-on-1 online chemistry class with a tutor who holds a master's in chemistry does what a classroom cannot: reads your answers and tells you which of the five reasons is yours, then teaches that. The mole rebuilt if it needs rebuilding, particles drawn until the picture is there, and the mark scheme used from the first month. For high school and AP Chemistry, IGCSE and GCSE, A-level, IB and CBSE Class 11 and 12. The free 30-minute first class is a real lesson on the topic you bring.
Questions parents ask
1Why is chemistry so hard?
2Why is chemistry so hard for me but easy for others?
3Is chemistry harder than physics?
4Is chemistry harder than biology?
5What is the hardest part of chemistry?
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Shobha
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Teaching maths, science and English to children online since 2018. 500+ students, 20+ tutors, families in nine countries.