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Chemical reactions that release heat are called exothermic. A burning log in the fireplace is an exothermic reaction: It gives off lots of heat. A dynamiteexplosion is exothermic, too. It releases a tremendous amount of energy in

seconds, energy in the form of heat, light, sound, and wave motion in the air!

BLASTS FROM THE PASTTo dig through thick stone, builders in the ancientworld, such as the Aztecs and the Romans, relied on aprimitive technique. They heated the rock theyneeded to move, then cooled it quickly. The suddentemperature change was supposed to make the rockcrack so the builders could break it apart. Whether itworked was a matter of chance.

About 1,000 years ago, the Chinese inventedgunpowder by combining charcoal, sulfur, andpotassium nitrate. In the 13th century, the Europeansmade a similar discovery and began usinggunpowder in weaponry and for blasting to clearbuilding sites. But gunpowder is very volatile; theslightest shock can set it off, and there were manyaccidents. What’s more, gunpowder blasts are noteffective in breaking up rock.

Finally, in 1846, Italian scientist Ascanio Sobrerocreated nitroglycerin, an extremely volatilecompound made up of nitrates and glycerol. It waspowerful enough to be valuable as a blasting agent,but too dangerous to use. A minor tremor couldcause an explosion.

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1 The blasting cap detonates, providing the initial shock that ignites a chemical reaction in the stick of dynamite.

2 The chemical reaction happens in a fraction of a second and travels from one end of the dynamite to the other.

3 The reaction produces a growing amount of hot gas, which forms amoving high-pressure zone.

4 The area in front of the chemical reaction is a low-pressure zone because the temperature stays the same. The change from low to highpressure happens so fast that a tremendous force is created.

5 This force can’t be contained in the stick of dynamite. And an explosionoccurs, blowing apart whatever is in its way.

AN INSIDE VIEW OF DYNAMITE

A BETTER WAYAlfred Nobel, a Swedishchemist, found a way topreserve nitroglycerin’sexplosive power anddecrease its volatility. First,Nobel mixed the nitroglycerinwith non-volatile clay. Themixture was much harder to detonate but, oncedetonated, was still powerful. He packed the mixtureinto cardboard tubes and attached a blasting cap—asimple wooden plug filled with gunpowder with afuse. Only by lighting the fuse and detonating thegunpowder could an explosive reaction be set off.The problem of unpredictable reactions was solved.

Dynamite was much safer than gunpowder ornitroglycerin alone, but there were occasionalaccidents. The nitroglycerin sometimes crystallized,meaning it was no longer mixed with the stabilizingclay. It could also sweat to the surface of the sticks orpuddle in the crates in which it was stored.

BigBangStockholm, Sweden, 1866Stockholm, Sweden, 1866

PEACE OF MINDAlfred Nobel was shocked to see

himself referred to in a newspaperas the “Merchant of Death.” To

counteract this perception, he established the NobelPrizes to be given for achievements in the sciencesand literature and, most important, for peace.

AN EXPLOSION OF USESThe Panama Canal connects the Atlantic and PacificOceans. By the time it opened in 1914, it had been adream for centuries. And dynamite made it happen.It took 67 million pounds (30.4 million kg) ofdynamite to move 175million cubic yards of earth(enough to fill the EmpireState Building 500 times).

Dynamite has been usedto prevent or minimizedamage, too. Because adynamite explosiondecreases the amount of oxygen in the air, ithelps contain fires, which need oxygen to burn.In 1991, during the Persian Gulf War, as Iraqitroops retreated from Kuwait, they set oil fieldson fire. The fires raged out of control. Americantroops exploded dynamite near the wells, andthe fires died down long enough for the troopsto cover the wells.

Nobel Prize medal

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HEAT WAVE You wouldn’t need a thermometer to tell youthat a dynamite explosion gives off heat. What aboutreactions that aren’t so dramatic? Try this: Put an outdoorthermometer in a clean jar with a lid. Wait five minutes.While you’re waiting, soak a small steel wool pad (withoutsoap) in 1/4 cup of vinegar for a minute or two. After the fiveminutes have passed, record the temperature in the jar,then remove the thermometer. Squeeze the steel wool asdry as you can (but don’t rinse it) and wrap it around thebase of the thermometer. Put the wrapped thermometerback in the jar and cover the jar with the lid. Wait fiveminutes, then take the temperature and record it. Unwrapthe thermometer, rinse, and dry it. Using a clean, dry jar anda dry (unsoaked) piece of steel wool, repeat the procedureand record the temperature. What happened? Why? Howwould you characterize the reaction that took place?

Heart patients are sometimes treated with nitroglycerin. It makes blood vessels

expand, enabling the blood to flow more freely and lowering blood pressure to help prevent heart attacks. The

amount of nitroglycerin in a tablet is tiny and

not harmful.

To make way for a new stadium, buildersdetonated dynamite to bring down theKingdome in Seattle, Washington.

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