How to Study for Chemistry in College: General Chemistry, Unit by Unit

Here is how to study for chemistry in a college General Chemistry course: put a unit on every number you write, get the mole and stoichiometry solid before anything else, work problems with the solution covered, and keep a log of every mistake until it stops recurring. Chemistry exams are mostly problems, so problems are how you study.

This guide makes that concrete for General Chemistry I and II: what the course covers (checked against three universities' course descriptions and the free OpenStax textbook), why it trips people up, a unit-by-unit table with a free place to practice each topic, how to take a chem exam, and what the standardized ACS final looks like.

Exam this week? Jump to how to take a chemistry exam and the catch-up plan.

What General Chemistry I and II cover

General Chemistry is usually a two-semester sequence, and course descriptions read much alike from campus to campus. Ohio State's CHEM 1210 lists dimensional analysis, atomic structure, the mole, stoichiometry, chemical reactions, thermochemistry, electron configuration, bonding, molecular structure, gases, liquids and solids. The University of Illinois describes CHEM 102 as atomic structure, bonding, states of matter, stoichiometry and chemical equilibrium. The University of Georgia sums up CHEM 1211 in one line: stoichiometry, structure, bonding and reactivity.

The free OpenStax Chemistry 2e textbook says it follows the scope and sequence of the two-semester general chemistry course. Its chapters map onto the two semesters like this:

The split varies. Illinois, for example, puts chemical equilibrium in its first semester, where many schools save it for the second. Some departments teach "atoms first," with electron structure before stoichiometry. Your syllabus's schedule decides what each exam covers.

College Board lists AP Chemistry's college equivalent as "A one-year, introductory college general chemistry course" (College Board). That makes Lykke's free AP Chemistry course a solid practice bank for Gen Chem I and II: it isn't your school's course, but it works through the same chemistry one topic at a time, and the table below links its sections.

Why general chemistry is hard

Most of the difficulty is in a few places you can name and work on.

• It's a math course in disguise. Nearly every problem is a chain of conversions: grams to moles, moles to moles through an equation, moles to liters or joules. Illinois lists credit in (or exemption from) a math course as a prerequisite for CHEM 102, and Ohio State requires a math placement level or a C- or better in a listed math course for CHEM 1210. The math is mostly algebra, scientific notation and, for pH, logarithms.
• Doing the math alongside it is risky. The University of Georgia's chemistry department reports that, in prior years' data, 60% of students who enrolled in precalculus (MATH 1113) and CHEM 1211 in the same semester failed or withdrew from CHEM 1211. Taking precalculus first improves those numbers, it says, and it strongly encourages students who still need precalculus to take its CHEM 1210, a basics course, and start CHEM 1211 the next semester (UGA Chemistry).
• The mole is the bottleneck. A study of 5,636 students in first-semester chemistry at a large public university, over four semesters, found that students in the bottom quarter of SAT math scores struggled across every topic but disproportionately on the mole concept and stoichiometry. The researchers found the gap wasn't explained by algebra-heavy topics alone, and the at-risk students who did well on the mole and stoichiometry went on to perform about as well as their peers (Ralph & Lewis, 2018).
• It's cumulative. Molarity uses the mole; titration uses molarity; equilibrium and acid-base problems use all of it. A shaky September unit is still costing you points in December.
• Concepts and calculations are tested together. You need to explain why a bond is polar or why a gas behaves non-ideally, and also compute a yield to three significant figures. A study routine that drills only one of those leaves a gap.

The hopeful part is the study's final result, about the students who did well on the mole. It shows a link, not proof that one causes the other, but it points to the mole and stoichiometry as the first place to put extra hours.

How to study for chemistry: five habits

The learning research behind recall, spacing and mixed practice is in our guide to studying for midterms. In a chemistry course, it comes down to five habits.

1. Do every calculation with dimensional analysis

OpenStax states the rule in one sentence: dimensional analysis means the units are multiplied, divided and canceled exactly like the numbers. Write every quantity with its unit, set up conversion factors so the unwanted unit cancels, and check that what remains is the unit the question asked for. For example, how many grams of NaCl are in 250. mL of a 0.150 M solution?

• 1. mL × (1 L / 1000 mL) × (0.150 mol NaCl / 1 L) × (58.44 g NaCl / 1 mol NaCl) = 2.19 g NaCl

Milliliters cancel, liters cancel, moles cancel, and grams are left. If you end up with g²/mol, you know the setup is wrong before you touch the calculator. This one habit covers unit conversions, molarity, gas stoichiometry and most of thermochemistry. Lykke's free Stoichiometry: The Mole Bridge demo shows the grams-to-moles-to-particles chain as a picture you can play with.

2. Work problems with the solution covered

Reading a worked example feels like learning; producing one is the test. For each example in your textbook or lecture notes, cover the solution, set up the problem yourself, and uncover it one line at a time only when you're stuck. Then do the end-of-chapter problems with the answers closed. When you check, compare the setup, not just the final number: a right answer from a wrong setup will fail on the next problem.

3. Keep an error log

Give each missed problem one line: where it came from, what went wrong, the cause and the fix. Chemistry errors tend to fall into a few causes, and naming them shows you which to drill:

Redo each logged problem from a blank page two or three days later, and again in the week before the exam. Our Calculus 1 guide uses the same log for math, which helps if you're taking both this semester.

4. Mix earlier units into every week

Homework sorted by section tells you which method to use. An exam doesn't. Once a week, do a short mixed set (two problems from each earlier unit) and name the method before you start: a limiting-reactant problem, a gas law, Hess's law, a dilution. This is also how a cumulative final stops being a surprise.

Before lecture, skim the section so the professor's examples aren't the first time you've seen the idea; our guide to taking notes in college covers how to keep up with a lecture full of worked problems.

5. Memorize the short list, and nothing else

Most of general chemistry is method, but a few facts have to be in your head because no problem gives them to you: the names, formulas and charges of the common polyatomic ions (nitrate, sulfate, phosphate, ammonium and the rest of your instructor's list), the solubility rules, which acids and bases are strong, the seven elements that exist as diatomic molecules (H2, N2, O2, F2, Cl2, Br2, I2) and the metric prefixes. Put them on flashcards in the first weeks and review them a few minutes at a time, because naming, net ionic equations and pH problems all assume them. Then find out what your exams supply, and don't spend time memorizing it: an ACS exam, for example, prints the periodic table and constants in the booklet.

How to pass general chemistry: a unit-by-unit practice plan

Work through the rows in your syllabus's order. Each link is free: the AP Chemistry sections explain the topic with quizzes and flashcards, and the demos let you change a variable and watch what happens.

A good week in any unit:

1. The day of each lecture, work that section's examples with the solutions covered and take the matching section's quiz.
2. Do the homework closed-book first, and log each miss.
3. Once a week, mix in earlier units and redo the logged problems that are due.
4. When a formula feels like symbol-pushing, open the demo and change one variable at a time.
5. Two weeks before an exam, switch to the 14-day plan with your department's old exams as the practice tests.

The federal credit-hour definition assumes at least two hours of out-of-class work each week for every hour of classroom instruction (34 CFR 600.2), so a 3-credit chemistry lecture plans on about 6 hours a week outside class, before any lab reports. Spread them across most days.

How to take a chemistry exam

Before exam day, read your syllabus for four rules and practice under them: whether a calculator is allowed (and which kind), whether you get a periodic table, whether constants and equations are supplied or you need to memorize them, and how answers are graded (significant figures, units, work shown).

On the exam:

1. Skim, then budget by points. Do the fastest questions first so a stuck equilibrium problem can't eat the time for three quick conversions.
2. Write units on every line. Dimensional analysis catches setup errors as you go, and graders can give partial credit only for work they can see.
3. Round once, at the end. Carry extra digits through a multi-step calculation and round the final answer. OpenStax's significant-figure rules: when you multiply or divide, keep as many significant figures as the measurement with the fewest; when you add or subtract, keep as many decimal places as the number with the fewest. Exact numbers, such as counts and defined conversions, don't limit you.
4. Check that the answer is chemically possible. A percent yield over 100%, a negative concentration or a pH of 15 for a weak acid means something went wrong.
5. Label your answer. Write "37.6 g AlCl3," not "37.6," and box it.
6. Answer "explain" questions with a reason. "Higher boiling point because of hydrogen bonding between molecules" earns credit; "stronger forces" may not.

What to know about the ACS general chemistry exam

Many departments give a standardized final written by the American Chemical Society's Division of Chemical Education Examinations Institute. Ask your instructor whether yours does, and which version. From the Institute's own pages:

• Length: the first-term, second-term and full-year general chemistry exams each have 70 questions in 110 minutes (the 2024 full-year exam allows 112). Brief versions have 50 questions in 55 minutes, and there are conceptual and paired-question versions with fewer questions (exam list). Seventy questions in 110 minutes is about 94 seconds each.
• Format and guessing: multiple choice, one mark per question, scored on right answers only. Because there's no penalty for a wrong answer, the administering directions tell instructors to advise students to answer every question.
• What you can bring: no reference material. Your instructor may allow a non-programmable calculator. The reference data you need, such as a periodic table and constants, is printed in the booklet, and instructors must account for every booklet when the exam ends.
• Scores: on the 2021 first-term exam, the national mean was 39.3 out of 70 (about 56%) and the median 38, across 2,660 students at 28 institutions. A raw score of 50 was at the 74th percentile (GC21F norms). How that turns into a grade is your instructor's decision: the Institute lets departments use its exams in whatever way works for their class.

Since the real exams stay secure, the official practice material is sold by the Institute: a General Chemistry study guide with over 600 problems, split into first-term and second-term halves of eight chapters each, and 50-question online practice exams for first-term, second-term and full-year material (study materials). The guide's chapter list doubles as a checklist. First term: atomic structure, electronic structure, formula calculations and the mole, stoichiometry, solutions and aqueous reactions, heat and enthalpy, structure and bonding, and states of matter. Second term: more solutions and aqueous reactions, kinetics, equilibrium, acids and bases, solubility equilibria, thermodynamics, electrochemistry and nuclear chemistry.

For a 70-question multiple-choice final, the practice that pays is timed mixed sets: 20 questions in 30 minutes, drawn from every unit, graded and logged.

Common general chemistry mistakes, and one worked example

1. Comparing grams instead of moles. Reactions happen in moles. Convert every mass first.
2. Skipping the mole ratio. A balanced equation's coefficients are the only bridge from one substance to another.
3. Picking the limiting reactant by eye. Neither the smaller mass nor the smaller number of moles tells you which reactant runs out. See the example below.
4. Rounding at every step. It drifts your answer away from the key's. Round once.
5. Mixing up mL and L, or °C and K. Molarity is per liter, and the gas laws need kelvins.
6. Forgetting that ΔH changes sign. Reverse a reaction in a Hess's law problem and the sign of its ΔH flips; multiply it by 2 and ΔH doubles.
7. Treating every acid as strong. A weak acid needs an equilibrium (ICE) setup; its pH isn't simply −log of its concentration.

Worked example: finding the limiting reactant

Aluminum reacts with chlorine: 2Al + 3Cl2 → 2AlCl3. You start with 10.0 g of Al and 30.0 g of Cl2. Which runs out, and how many grams of AlCl3 can form?

1. Convert both to moles. 10.0 g Al × (1 mol / 26.98 g) = 0.371 mol Al. 30.0 g Cl2 × (1 mol / 70.90 g) = 0.423 mol Cl2.
2. Use the ratio to test one reactant. All the aluminum would need 0.371 mol Al × (3 mol Cl2 / 2 mol Al) = 0.556 mol Cl2. You have only 0.423 mol, so chlorine is the limiting reactant and aluminum is in excess.
3. Find the product from the limiting reactant. 0.423 mol Cl2 × (2 mol AlCl3 / 3 mol Cl2) = 0.282 mol AlCl3. At 133.33 g/mol, that's 37.6 g of AlCl3.
4. Check what's left. The reaction uses 0.282 mol of Al, or 7.61 g, so 2.39 g of aluminum is left over.

The trap: aluminum has the smaller mass (10.0 g against 30.0 g) and the smaller number of moles (0.371 against 0.423), so both shortcuts point at aluminum. That route predicts 49.4 g of product, an answer that's 31% too high. Only the mole ratio gets it right. OpenStax works another case in its section on reaction yields, and the AP Chemistry section on stoichiometry has more to practice on.

How to catch up in general chemistry

If you're behind at midterm time, triage from the next exam rather than restarting the textbook.

1. List what the next exam covers, and make that the whole plan until exam day.
2. Fix the mole first. If you can't move between grams, moles and particles without notes, start there: it's what the later units are made of. High School Chemistry's section on stoichiometry and the mole rebuilds it from scratch if your last chemistry class was a while ago.
3. Rebuild each topic with one example and three problems. Read one worked example, close it, solve three similar problems, and log what you miss.
4. Do the grade math. Check the syllabus for dropped quizzes, a final that replaces a low exam or curves, and work out what you need on the rest.
5. Get help this week. Bring your error log to office hours, your department's help room or your campus tutoring center, and ask about one specific problem.
6. Decide before the deadline. If the numbers don't work, talk with your instructor and advisor before your school's withdrawal date; our guide on whether to drop a class walks through the trade-offs, including financial aid.

Free resources for general chemistry

• OpenStax Chemistry 2e: a free textbook for the two-semester course, online or as a PDF, with worked examples and end-of-chapter exercises. A second explanation for any chapter of your own book.
• MIT OpenCourseWare 5.111SC: MIT's intro chemistry, with lecture videos, problem sets with solutions and exams with answer keys. 5.112 is the version for students with a strong chemistry background. Both lean more on electronic structure than a typical first semester.
• Khan Academy chemistry: free videos and practice by topic, including stoichiometry and limiting reactants.
• LibreTexts General Chemistry: free general chemistry textbooks, useful when you want a third explanation.
• Your department's old exams: the closest rehearsal for the real thing. Ask whether they're posted.
• Lykke's free AP Chemistry course: intro college-level chemistry by topic, with quizzes and flashcards. When Gen Chem II is behind you, our organic chemistry guide covers what comes next.