50 Fun Facts About Chemical Reactions

Which metal forms the skin of the Statue of Liberty, which turned from shiny brown to green by reacting with air?

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.

Which candy makes Diet Coke erupt in a geyser, not by a chemical reaction but by helping dissolved gas escape?

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.

What forms inside a disposable hand warmer as the powder in it reacts with air and heats up?

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.

Which liquid from the medicine cabinet breaks down into water and oxygen to make the foam called elephant's toothpaste?

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.

Which kitchen powder fizzes with vinegar in a model volcano because the reaction gives off carbon dioxide gas?

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.

Which insects react a chemical called luciferin with oxygen inside their abdomens after dark?

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.

How does the light of a glow stick change in hot water, since heat speeds up the reaction inside?

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.

The fire triangle is a simple model of the three things every fire needs: heat, oxygen and what else?

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.

Which reaction in green leaves uses sunlight to turn carbon dioxide and water into sugar and oxygen?

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.

Which household cleaner must never be mixed with ammonia, because the two react to release toxic chloramine fumes?

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.

In a chemical equation, what name is given to the new substances written on the right-hand side of the arrow?

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.

When a chemical equation is read aloud, which word is spoken for the arrow between the two sides?

Yields is used instead of an equals sign because a reaction has a direction. The arrowhead always points toward the new substances being made.

In the balanced equation 2H₂ + O₂ → 2H₂O, what are the large numbers written in front of the formulas called?

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.

What is a substance that speeds up a chemical reaction without being used up, like the platinum in a car exhaust?

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.

Which reaction type follows the pattern AB → A + B, as when electricity splits water into hydrogen and oxygen?

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.

Which reaction type is A + BC → AC + B, as when zinc pushes hydrogen out of an acid?

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.

What do chemists call the cloudy solid that suddenly appears when two clear solutions are mixed and react?

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.

Which type of medicine works by neutralization, using a mild base to settle heartburn and indigestion?

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.

Which French chemist showed by careful weighing that mass is never lost in a reaction, then died on the guillotine?

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.

Which protein molecules, such as the amylase in saliva, speed up the chemical reactions inside living things?

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.

Which word describes a reaction that takes in heat from its surroundings, so that its container feels cold to the touch?

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.

Which mixture of aluminum powder and iron oxide burns hot enough to weld railway tracks together?

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.

Which term, coined by Svante Arrhenius, names the hurdle that molecules must clear before they are able to react?

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.

A cloud of flour dust in a mill can explode, unlike a sack of flour, because the particles expose far more what?

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.

The chemistry mnemonic OIL RIG reminds students that oxidation is loss, and reduction is gain, of which particles?

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.

In a chemical equation, what does a double arrow pointing both ways (⇌) tell you about the reaction?

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.

When wood burns to ash and smoke, what happens to its atoms, according to the law of conservation of mass?

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.

Which sugar do the body's cells combine with oxygen in cellular respiration, releasing energy, carbon dioxide and water?

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.

Which single-celled fungus makes bread dough rise by turning its sugars into carbon dioxide gas and alcohol?

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.

Which everyday item has been made for thousands of years by reacting fats or oils with a strong alkali such as lye?

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.

Which browning process between sugars and amino acids, named after a French chemist, flavors seared steak and toast?

The Maillard reaction only gets going at about 140 °C, hotter than boiling water, which is why boiled food never browns. Its discoverer was trying to work out how the body builds proteins.

Which dye made from lichens turns red in acids and blue in bases, and is sold soaked into paper test strips?

Litmus was first used to study acids and bases around the year 1300 by a Catalan physician. It lives on in everyday speech, where a litmus test is any single question that settles a matter.

Which corrosive liquid, made by the lining of the human stomach, gives off hydrogen gas when zinc is dropped into it?

Hydrochloric acid keeps the stomach at a pH of about 1 to 2, which helps digest food and kills most swallowed microbes. A base released further along the gut cancels it out again.

Which pale rock made of calcium carbonate fizzes in acid and is slowly dissolved by acid rain on old cathedrals?

Limestone caves exist for the same reason. Rainwater dissolves the rock a little at a time, which is why most of the world's cave systems are found in it.

Which poisonous gas with no color or smell forms when gas, wood or coal burns without enough oxygen?

Carbon monoxide forms when a flame is starved of air, which is why a faulty heater in a closed room is so dangerous. Homes need alarms for it because human senses cannot detect it at all.

The Haber process makes ammonia for fertilizer by combining hydrogen with which gas, the main ingredient of air?

Nitrogen makes up about 78% of the air but is so stable that it hardly reacts with anything. Forcing it to combine takes great heat and pressure, plus powdered iron to help it along.

Which lifting gas is safer than hydrogen in airships because it almost never takes part in chemical reactions?

Helium is chemically inert, so a stray spark cannot set it alight. Hydrogen lifts a little better but burns fiercely, as the airship Hindenburg showed when it caught fire in 1937.

Silver spoons turn black by reacting with a gas containing which yellow element, also behind the stink of rotten eggs?

Sulfur reaches the silver as traces of hydrogen sulfide in the air, and the dark film it leaves is called tarnish. Museums rub it away with a very gentle abrasive such as calcium carbonate.

Which imaginary fire-like substance did chemists of the 1700s wrongly believe escaped from anything that burned?

Phlogiston takes its name from the Greek for 'burning up'. The idea collapsed once careful weighing in closed vessels showed that burning things take in a gas from the air instead.

Which English church minister isolated oxygen by heating a mercury compound, and also invented carbonated water?

Joseph Priestley tested his new gas on mice, which surprised him by surviving a long time in it, and then breathed it himself. He claimed that science was only a hobby.

Which metal, named after a Scottish village, gives fireworks and emergency flares their deep red color?

Strontium takes its name from Strontian in Scotland, where its ore was found in 1790. Chemists recognized it as a new element from the crimson color it gave to a flame.

Which scientist's Christmas lectures for children at the Royal Institution explained chemistry using one candle?

Michael Faraday founded the Christmas lectures for young people in 1825, and they are still given every year. He told his audience that many of the candle experiments could be tried at home.

Which mixture of two strong acids can dissolve gold, and was once used to hide Nobel Prize medals from the Nazis?

Aqua regia means 'royal water' in Latin. When Germany invaded Denmark, a chemist dissolved two gold Nobel medals in it, left the jar on a laboratory shelf, and recovered the gold after the war.

Which branch of chemistry uses balanced equations to calculate exactly how much of each substance a reaction needs?

Stoichiometry comes from Greek words meaning 'element' and 'measure'. It works like scaling up a recipe, with the balanced equation giving the proportions of every ingredient.

What do chemists call the ingredient that runs out first and stops a reaction, like buns before the hot dogs?

The limiting reagent sets a ceiling on how much a reaction can make, however much of everything else is on hand. Whatever is left over at the end is said to be in excess.

Which idea explains reaction rates by saying molecules must meet with enough energy and in the right orientation?

Collision theory explains why most meetings between molecules come to nothing. Only the few that are hard enough, and lined up the right way, break old bonds and form new ones.

Which French chemist's principle says a reaction at equilibrium shifts to counteract any change made to it?

Henry Le Chatelier set out the rule in 1884. It is why ammonia plants run at a compromise temperature, since cooler conditions favor more ammonia but make the reaction too slow.

Which chemical do crime-scene investigators spray because it glows blue on reacting with the iron in blood?

Luminol glows for only about 30 seconds each time it is sprayed. Investigators therefore work in a darkened room and record the faint blue light with a long-exposure photograph.

Which insect defends itself by mixing chemicals inside its abdomen to fire a near-boiling, foul spray at attackers?

The bombardier beetle keeps its chemicals in a reservoir and lets them into a second chamber only when threatened. The reaction there heats the spray almost to the boiling point of water.

Which liquid turns blue-black when dripped onto starchy foods such as bread or potato?

Iodine and starch together make an intense blue-black color, a reaction first described in 1814. It is still the standard school test for starch in food and in plant leaves.