Chemical Reactions
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50 free Chemical Reactions trivia questions with answers — science & nature quiz, new questions added Oct 2026.
A chemical reaction is what happens when substances stop being themselves and turn into something new. It is why a statue changes color over the years, why a cake rises in the oven, why a glow stick lights up when you snap it and why a campfire leaves only ash behind. Once you know what to look for, you see reactions everywhere. This quiz covers the ground a middle school or early high school class does. There are questions on the main reaction types and how to spot them from an equation, on reading and balancing equations, on reactions that give out heat and reactions that take it in, and on what makes a reaction go faster or slower. Others look at the chemistry of the kitchen, the medicine cabinet and the natural world, and at the scientists who first worked out the rules. The opening questions are easy enough for kids and for anyone who remembers a little school science, and the later ones will stretch a student revising for a test. Every answer comes with a short explanation, so a wrong guess still teaches you something. You can play online or print the questions for a classroom.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which metal forms the skin of the Statue of Liberty, which turned from shiny brown to green by reacting with air?
Copper
Copper on the statue was reddish-brown and shiny when it was built, but within twenty years it had turned green. That green layer now protects the metal underneath from further corrosion.
Q 02Which candy makes Diet Coke erupt in a geyser, not by a chemical reaction but by helping dissolved gas escape?
Mentos
Mentos are covered in millions of microscopic pits, and each one gives the dissolved carbon dioxide a place to form bubbles. Nothing new is made, so the eruption counts as a physical change.
Q 03What forms inside a disposable hand warmer as the powder in it reacts with air and heats up?
Rust
Rust gives off heat as it forms, and that is the whole trick. Tearing open the wrapper lets air reach the iron, and the pouch then stays warm for many hours.
Q 04Which liquid from the medicine cabinet breaks down into water and oxygen to make the foam called elephant's toothpaste?
Hydrogen peroxide
Hydrogen peroxide normally breaks down far too slowly to notice. The demonstration adds a helper chemical to speed it up, and dish detergent to trap the escaping oxygen as a column of hot foam.
Q 05Which kitchen powder fizzes with vinegar in a model volcano because the reaction gives off carbon dioxide gas?
Baking soda
Baking soda does the same job in cakes and cookies. An acid in the mix, such as cream of tartar, sets off the gas that puffs up the dough.
Q 06Which insects react a chemical called luciferin with oxygen inside their abdomens after dark?
Fireflies
Fireflies make what scientists call cold light, a glow with no infrared in it. The firefly's light-making chemistry is now borrowed for forensic work and medical tests.
Q 07How does the light of a glow stick change in hot water, since heat speeds up the reaction inside?
Brighter but fades sooner
It glows brighter but fades sooner, and the trick works the other way too. A glow stick left in the freezer turns dim, yet it lasts far longer because the cold slows the reaction down.
Q 08The fire triangle is a simple model of the three things every fire needs: heat, oxygen and what else?
Fuel
Fuel is the side of the triangle that runs out by itself, since a fire with nothing left to burn simply stops. Take away any one of the three and the flames die.
Q 09Which reaction in green leaves uses sunlight to turn carbon dioxide and water into sugar and oxygen?
Photosynthesis
Photosynthesis made, and still tops up, the oxygen in Earth's atmosphere. It also supplies most of the energy that complex life runs on, because nearly every food chain starts with it.
Q 10Which household cleaner must never be mixed with ammonia, because the two react to release toxic chloramine fumes?
Bleach
Bleach and ammonia do not give off chlorine gas, as many people think. They react to make chloramines instead, which are still dangerously toxic to breathe.
Q 11In a chemical equation, what name is given to the new substances written on the right-hand side of the arrow?
Products
Products usually behave nothing like the substances that went in. That is how explosive hydrogen and the oxygen that feeds a fire can combine into water, which puts fires out.
Q 12When a chemical equation is read aloud, which word is spoken for the arrow between the two sides?
Yields
Yields is used instead of an equals sign because a reaction has a direction. The arrowhead always points toward the new substances being made.
Q 13In the balanced equation 2H₂ + O₂ → 2H₂O, what are the large numbers written in front of the formulas called?
Coefficients
Q 21Which word describes a reaction that takes in heat from its surroundings, so that its container feels cold to the touch?
Endothermic
Endothermic reactions pull heat in, so whatever they touch gets colder. A classic classroom demonstration mixes two solids that turn cold enough to freeze water.
Q 22Which mixture of aluminum powder and iron oxide burns hot enough to weld railway tracks together?
Thermite
Thermite carries its own oxygen, locked inside the iron oxide. It therefore needs no air at all, and can even be used for welding under water.
Q 23Which term, coined by Svante Arrhenius, names the hurdle that molecules must clear before they are able to react?
Activation energy
Coefficients are the only numbers a chemist may change to balance an equation. Changing the small subscripts instead would turn water into a completely different substance.
Q 14What is a substance that speeds up a chemical reaction without being used up, like the platinum in a car exhaust?
Catalyst
A catalyst comes out of the reaction unchanged, so it can be used again and again. That is why a thin coating of precious metal can clean a car's exhaust fumes for years.
Q 15Which reaction type follows the pattern AB → A + B, as when electricity splits water into hydrogen and oxygen?
Decomposition
Decomposition is the exact opposite of synthesis, with one compound coming apart into simpler pieces. A lightning-fast version of it inflates a car's airbag in a crash.
Q 16Which reaction type is A + BC → AC + B, as when zinc pushes hydrogen out of an acid?
Single replacement
Single replacement means one element takes another's place inside a compound. It only happens when the newcomer is the more reactive of the two, so zinc can do it to an acid but gold cannot.
Q 17What do chemists call the cloudy solid that suddenly appears when two clear solutions are mixed and react?
Precipitate
A precipitate forms when one of the new compounds cannot stay dissolved. In the 'golden rain' demonstration, two colorless solutions are mixed and a vivid golden-yellow solid appears.
Q 18Which type of medicine works by neutralization, using a mild base to settle heartburn and indigestion?
Antacid
An antacid reacts with the acid in the stomach and cancels it out. Many chewable tablets use calcium carbonate, the same compound found in chalk, eggshells and seashells.
Q 19Which French chemist showed by careful weighing that mass is never lost in a reaction, then died on the guillotine?
Antoine Lavoisier
Antoine Lavoisier measured more precisely than anyone before him. He was executed in 1794 because of his other career, collecting taxes for the crown, and not because of his science.
Q 20Which protein molecules, such as the amylase in saliva, speed up the chemical reactions inside living things?
Enzymes
Enzymes such as amylase are the reason plain rice or potato starts to taste sweet as you chew. The starch is already being broken down into sugar before you swallow.
Activation energy is why a mix of gas and air sits harmlessly in a stove until a spark arrives. Heating things up helps because more of the molecules then carry enough of it to react.
Q 24A cloud of flour dust in a mill can explode, unlike a sack of flour, because the particles expose far more what?
Surface area
Surface area decides how fast a solid can burn, because only the outside of each grain touches the air. A flour-dust blast destroyed a Minnesota mill in 1878 and killed 18 people.
Q 25The chemistry mnemonic OIL RIG reminds students that oxidation is loss, and reduction is gain, of which particles?
Electrons
Electrons change hands whenever something burns or corrodes. The word oxidation is a leftover from the days when chemists thought oxygen always had to be involved.
Q 26In a chemical equation, what does a double arrow pointing both ways (⇌) tell you about the reaction?
It is reversible
It is reversible, meaning the new substances can turn back into the old ones. Left alone, such a reaction settles into a balance in which both directions run at the same speed.
Q 27When wood burns to ash and smoke, what happens to its atoms, according to the law of conservation of mass?
They are rearranged
They are rearranged into new substances, never created or destroyed. Catch all the smoke, gases and ash from a fire and they would weigh the same as the wood plus the oxygen it used.
Q 28Which sugar do the body's cells combine with oxygen in cellular respiration, releasing energy, carbon dioxide and water?
Glucose
Glucose is technically being burned inside every cell. It happens so slowly, and in so many small steps, that the body can capture the energy instead of going up in flames.
Q 29Which single-celled fungus makes bread dough rise by turning its sugars into carbon dioxide gas and alcohol?
Yeast
Yeast makes the same two things when beer is brewed. Bakers want the gas, which puffs up the dough, while brewers are after the alcohol.
Q 30Which everyday item has been made for thousands of years by reacting fats or oils with a strong alkali such as lye?
Soap
Soap-like material was already being made in ancient Babylon around 2800 BC. The reaction splits each fat molecule apart and sets free glycerin, which is sometimes left in the bar to soften it.