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July 04, 2007

Loaded with bear

Calories are a measure of heat. A small calorie is the amount of heat it takes to raise a gram of water from 3.5 degrees centigrade to 4.5 degrees centigrade. A large Calorie (capital C, also called a kilocalorie) is the amount of heat it takes to raise a kilogram of water (2.2 lbs) from 3.5o C. to 4.5o C. (OK, technically these are 4o calories, so don't write me to complain). The "Calories" we read about in nutrition are large calories. The prototypical male weighs 70 kg. So 70 Calories of heat energy released from food is enough to heat him up one degree centigrade. That's enough to be called a "fever." This seems like a lot of heat, especially as most people eat around 2500 Calories a day. Since there is usually a substantial heat difference between us and the environment and we also lose heat by evaporating water (sensible and insensible water loss), we manage to get rid of the excess we need to keep our bodies at 37o C. (body temperature in centigrade). More on this at the old site here. This post is about the surprisingly large amount of energy in a small amount of sugar. In particular, the energy in one little gummi bear.

The energy in a gummi bear is mainly locked up in table sugar (sucrose). Sucrose is a carbohydrate (a disaccharide, meaning it is made up of two subunits of smaller sugars, glucose and fructose). Each of these is itself a structure made of carbon, hydrogen and oxygen atoms connected in a particular pattern. If you think of the atoms as analogous to bricks and think of a building as made up of these bricks, you will understand two things. One, it takes energy to assemble the bricks into a building. That's the job of the construction trades. The other is that if the building comes tumbling down it releases a lot of energy in the process. Sometimes you have to put in some work to get the building to fall down but when you do it releases more energy than you put into it. That's what's happening with the sucrose in the gummi bear. There is a lot of energy locked up in the structure that gets released when we let it come apart. It comes apart by combining with oxygen and disintegrating.

You can see the remarkable amount of energy in the small amount of sucrose in a single gummi bear by a demonstration. The video below has made the rounds on the internet so you may have seen it before, but there was no explanation for most of the postings. In the demo a gummi bear is dropped into a test tube that has melted potassium chlorate in it. Potassium chlorate is one atom of potassium, one of chlorine and three atoms of oxygen. In other words, it is oxygen rich and is frequently used in highschool chemistry laboratories to generate oxygen gas. One way to do it is just to heat the potassium chlorate, which is a white powder, in a test tube until it melts.

The gummi bear is mainly sucrose (what did you think it was made out of? bear meat?). When it comes in contact with the oxygen in the test tube some of the sucrose disintegrates and this releases heat energy. The released heat causes the potassium chlorate to release more oxygen and a positive feedback loop develops.

Here's the result.

Cross-posted by Revere at Effect Measure


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I never expected Gummi Bears to be made of bear meat. "Gummi" is German for rubber. Gummi Bears should be made out of rubber. But I suppose they're probably made out of sucrose and pectin. Pectin is a polysaccharide that would react with the chlorate as well. Rubber would also react with molten potassium chlorate, but probably more slowly. Bear meat would too, for that matter.

I've welcomed the new calorie labeling in deciding what to buy fast food places. It instantly reveals what I could only guess before and I've been surprised how misguided some of my guesses were. Who would have thought a smallish carrot muffin could be so calorie-heavy?

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