Reaction Lab
Students can balance an equation on paper and still think burning steel wool gets lighter. Reaction Lab puts the reaction in a sealed flask on a scale, so they watch every atom move and the reading stay put.
Using this with a class? Make a free class and add your students yourself: each gets a username and password, with no email or Google account needed. Or give them one join code. Using Google Classroom? Post the link there; with a free class, the link also puts each student in your class, so you see their work. mytekDev is also available from the Google Workspace Marketplace, so your school's Google admin can install it for everyone.A first lesson: One period: balance water and burning methane, run one unbalanced on purpose, then take the lid off and do the zip bag lab beside the real one. A second period for the puzzles and the lab sheet.
Set up a free class Share to Google ClassroomWhat a student actually does
A sealed glass flask sits on a digital scale. Inside it, the molecules of the reaction drift: gases anywhere, liquids low, solids in a pile on the bottom. They are ball-and-stick models in the colors chemists use, and every atom carries its letter. Under the flask the equation is a row of cards, one per substance, each with a + and a − button. The student balances it by adding and taking away whole molecules. The small numbers in a formula cannot be changed: pressing one explains that changing it would make a different substance.
React plays the reaction in four stages: the molecules bump into each other, their bonds let go, each atom travels to a place in a new molecule, and the new bonds form. A graph beside the flask draws the mass the whole way, and a card shows the atoms of each kind before and after as rows of balls, so the count can be read without reading numbers. Tap an atom first and its path stays drawn. When the equation is balanced, the scale does not move. When it is not, the app plays what the equation claims: atoms that vanish, or atoms that come from nowhere, and the scale jumps.
Take the lid off and any gas the reaction makes escapes out of the open top, and the scale goes down by exactly its mass while the molecules wait in the room above. Three reactions have a lab bench: the zip bag of baking soda and vinegar, steel wool burning, and a candle, each on a kitchen scale in grams with a magnifier the student drags over it to see the particles. There are 17 reactions for middle school and 10 more at the high school level, five puzzles, and a lab sheet to hand in.
Water with an oxygen atom too many. The equation says that atom vanished, so the app plays exactly that: it fades, a red ghost stays where it was, and the scale drops from 34 to 18. A real sealed flask never does this, and that is the lesson.
What they are learning while they work
Nothing here is presented as a lesson. This is what the activity is made of.
| What the student does | What it is |
|---|---|
| Adds a hydrogen molecule because the oxygen row on the Atoms card says ≠ | Atoms are conserved. A balanced equation has the same number of each kind of atom on both sides. The card counts by kind, not in total, because a total can match while the kinds do not. |
| Watches the scale stay at 36 while three molecules become two | Mass is conserved because atoms are. Each kind of atom has its own mass wherever it is, so the same atoms weigh the same however they are joined. The number of molecules is allowed to change. |
| Presses the 2 in H₂O to make the count work | Subscripts and coefficients. The small number is part of the substance: H₂O₂ is hydrogen peroxide, not water. Balancing changes how many whole molecules there are, never what they are. |
| Runs water unbalanced and sees an oxygen atom fade out | What an equation claims. An equation is a claim about atoms. An unbalanced one says atoms were made or destroyed, and the app shows that claim happening so it can be seen to be wrong. |
| Takes the lid off burning methane and sees the scale drop | Open and closed systems. In an open container a gas can leave and take its mass with it. The atoms still exist in the room, so the mass did not disappear: it left. |
| Burns steel wool on the lab bench and the reading goes up | Mass from the air. Oxygen from the air joins the iron, so the solid weighs more. The magnifier shows the oxygen molecules coming apart and their atoms joining the iron. |
| Follows one carbon atom from methane into carbon dioxide | Atoms regroup. In a chemical reaction the atoms of the starting substances are regrouped into different molecules with different properties. Nothing about the atom itself changes. |
How to tell whether it landed
Ask, and let them show you. A student who has understood it can answer these without help.
- Three molecules went in and two came out. Why did the scale not change?
- Why can't you balance H₂ + O₂ → H₂O by writing H₂O₂?
- N₂ + H₂ → NH₃ has four atoms on each side. Is it balanced? How do you know?
- With the lid off, the scale went down. Where is that mass now?
- Steel wool gets heavier when it burns. Where did the extra mass come from?
- Your classmate's equation made an atom vanish when it ran. What would you tell them to change?
Use it in your subject
Not a technology class? Then the app is how students show what they learned in your unit. More projects for every subject.
Middle school physical science
MS-PS1-5 directly: a digital model of atoms in a reaction, the number of each kind of atom unchanged, and so the mass. It also models molecules and extended structures for MS-PS1-1, and the lab bench pairs with the before-and-after evidence of MS-PS1-2.
High school chemistry
The start of the equations unit and HS-PS1-7: typed coefficients, atomic mass units to two places, the mass of each side added up, and the odd-oxygen puzzle that makes students double an equation. Moles and grams of a real sample are not in it yet.
Life science
Photosynthesis and respiration are on the shelf as their net equations, with a note that a cell does each in many steps. The same atoms go round: carbon dioxide and water in, sugar and oxygen out, and back.
Homeschool and co-ops
The flask, the scale and the lab bench stand in for a balance and glassware, and the zip bag lab is the one real experiment worth doing at the kitchen table beside it.
Practical notes
- AgesGrades 6 to 8 are the home ground: students balance with whole molecules and read the scale in mass units, which keeps symbolic balancing and atomic masses out of what they are graded on, as MS-PS1-5 does. The high school level adds typed coefficients and atomic mass units for grades 9 and 10.
- TimeOne period for water, methane, an unbalanced run and the lid. A second for the lab bench, the puzzles and the sheet.
- EquipmentA computer or Chromebook with a modern browser. Nothing to install. A projector for Big screen, where the space bar runs the reaction one stage at a time. A printer if you want the sheet on paper.
- CostFree. The app has no paid tier.
- PrepRun water both ways yourself, about ten minutes: one of each and press React, then balance it and press React again. Then take the lid off methane. That is the whole demo.
- In a groupOpen Setup in the app's header: the level, which reactions are on the shelf or one reaction for everyone, whether a reaction only counts once it has also been run unbalanced, the sheet's questions, up to ten of your own, and a printed answer key.
For co-ops, microschools, and classrooms
Set it up once in Setup and hand the project out as the starter; the setup travels with it. With a free account the students' sheets come back to you as saved projects, with their answers and the reactions they balanced.
Common questions
Is it free?
Yes. Reaction Lab has no paid tier, and it can be tried right on this page without an account.
Does it replace the real lab?
No. Do the zip bag lab too; the app's lab bench is there to sit beside it. One thing to know: a sealed bag that puffs up a lot can read a few tenths of a gram low, because the bigger bag is lifted a little by the air it pushes aside. A capped plastic bottle does not puff up and shows no change. Use a scale that reads tenths of a gram.
Why can't students change the small numbers?
Because changing a subscript makes a different substance. It is the most common way students get a balanced-looking equation that means nothing, so the app does not allow it and explains why when they try.
Is this how a reaction really happens?
It shows where the atoms end up, not the exact way they get there. Real molecules break apart and join in many small steps, and atoms of one kind cannot be told apart, so a followed atom's path is one way it could go. How it works in the app says so.
Is the chemistry accurate?
Every equation, formula and atomic mass was checked against sources, along with every sentence a student reads. What is simplified on purpose is listed in the app: salts are drawn as touching clusters, ball sizes are shrunk so the bonds show, and the glow of a flame is drawn but never weighed.
Which reactions are in it?
Seventeen for middle school, among them water, burning methane, rust, steel wool, baking soda and vinegar, photosynthesis and respiration. Ten more at the high school level, among them propane, ethanol, the airbag and the yellow lead iodide.
Does it run on Chromebooks?
Yes. It draws in 2D in the browser with nothing to install, and it has a Big screen mode for a projector.
Still have a question? Ask us, and a person will write back.
Where to go next
Start with Reaction Lab
Trying it costs nothing and takes about five minutes. An account is what makes the work last.
Reaction Lab is one of the making apps on the platform. The atom colors are the ones chemists use in molecule models, every atom carries its letter so color is never the only clue, and the masses are the standard atomic weights.
Page last reviewed November 2026.
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