ChemUnlocked

High school chemistry homework help, study guides, and practice problem solutions that build real understanding.

Simple homework help with clear study guides, step-by-step worked examples, detailed solutions, and 2,642 practice problems sortable from easy to hard, by chemistry topic, and by type — built to help you actually understand the material, not memorize your way through it.

Start with your chemistry unit → Try chemistry practice problems →
15 units · 2,642 practice problems Easy, medium & hard difficulty Free to use Works unit by unit — start anywhere

How ChemUnlocked helps you learn high school chemistry

Understand

Study guides that explain the ideas, not just the formulas

Every unit starts with a guide, not a formula sheet. It walks through why the concept works and when to use it, so when a test question looks unfamiliar, you can still work out what to do.
Practice

Practice problems that show what you know

The practice sets change every time — new numbers, new setups — so memorizing last week's answers won't help. Filter by difficulty, work through a set, then check your reasoning against the full worked solution to see exactly where it broke down.
Study smart

Study skills that make the material stick

Rereading feels like studying, but it rarely builds memory you can use under pressure. These guides cover what does: spacing out review, testing yourself before you feel ready, and studying in a way that holds up once your notes are closed.
Practice Problems

Use practice to check your understanding before the test does

Choose a unit, filter by difficulty — easy, medium, or hard — and start with a Quick Set of 3 to see where you stand. Move into Standard Sets of 9 or Extended Sets of 18 when you want a longer review block. The goal isn't just a right answer — it's catching where your thinking went off track before that shows up on the test.

Open the chemistry practice hub → Browse practice by unit →
practice problems
2,642
unit banks
15
difficulty levels
3
15 Units

Pick the chemistry unit you need right now

Start with the topic your class is on, or go back and rebuild a unit that never fully clicked the first time. Not sure where to start? Go back one unit further than you think you need to. Don't skip straight to random practice when things aren't clicking. Fix the foundation first, then come back and test it.

01 Intro to Chemistry & Lab Safety 02 Matter 03 Atomic Structure 04 Electron Configuration 05 Periodic Table & Trends 06 Nomenclature 07 Moles 08 Chemical Reactions 09 Stoichiometry 10 Chemical Bonding 11 Energy & Thermochemistry 12 Gas Laws 13 Solutions 14 Chemical Equilibrium 15 Acids & Bases
See all chemistry practice by unit → Learn how to study chemistry more effectively → See how ChemUnlocked is built to help you study →
Study Skills

Get more out of the time you already spend studying chemistry

See all study skills guides →

These guides show you how to study chemistry in a way that leads to stronger recall, better problem solving, and fewer false signals that make you think you know it when you do not.

Guide 01 · 6 min read

How to Study Smarter, Not Longer

Small changes — mixing topics, switching up how you study — usually teach you more than another round of rereading.
Read the study guide →
Guide 02 · 7 min read

Why Practice Tests Beat Rereading

Testing yourself does more than check your answers. It's one of the fastest ways to build memory you can actually use.
Read the study guide →
Guide 03 · 6 min read

The Flashcard Method That Works

If flashcards have not been helping, the problem is usually the way they are written or used, not the idea of flashcards itself.
Read the study guide →
Guide 04 · 8 min read

Why Practice Beats AI Answers

Quick answers can finish homework without teaching the solving process. This guide shows why practice and worked solutions usually prepare you better for quizzes and exams.
Read the study guide →
See all study skills guides →
Common Questions

Chemistry homework help & practice — frequently asked questions

Quick answers before you dive in. Have a different question? Reach out — we read every message.

Is ChemUnlocked free to use?
Yes. Every study guide and a set of free sample practice problems are available at no cost, no account required. Premium unlocks longer practice sets — Quick, Standard, and Extended — across all 15 units if you want more reps.
What chemistry topics does ChemUnlocked cover?
All 15 core high school chemistry units, from lab safety and significant figures through gas laws, solutions, chemical equilibrium, and acids & bases. See the full unit list.
How many chemistry practice problems are there?
2,642 practice problems across all 15 units, split between calculation, concept, and multi-step questions — each with a full worked solution.
Can I practice by difficulty level?
Yes. Every unit's problem bank is sorted into easy, medium, and hard, so you can build up gradually from the basics or filter straight to the problems that actually challenge you before a test.
Do the practice problems come with answers and worked solutions?
Yes. Every problem includes a full worked solution, so you can check your reasoning against the answer, not just whether your final number matched.
How is ChemUnlocked different from AI answer generators?
ChemUnlocked is built to teach the solving process, not just hand you an answer. Problem sets are randomized each time, so memorizing one version will not help on the next — you actually have to understand the method. Read more in Why Practice Beats AI Answers.
High School Chemistry · Study Guides & Practice Problems