Perpetual motion in chemistry?

Today 25 Inventions Are The Best Thing Since Sliced Bread appeared in my Facebook feed. I’m a bit of a sucker for gadgety things, so I clicked through and had a look.

The ironing board mirror didn’t inspire me (given my normal lack of love for ironing boards, this seems like a short step to 7 years bad luck), but I wish my local council would invest in hourglass traffic lights, I want to know where I can buy universal wrapping paper and the pizza scissors are going on my Christmas list.

useful-inventions-36And then I got to item number 25, the reusable candle.


As you’ll see if you follow the link, the following text sits under the picture: “Image credits: Benjamin Shine (h/t: boredpanda via remarkably)”

The first link, the one that mentions Benjamin Shine, links to a page describing him as a British artist and designer. I hadn’t heard of him, so I reached for Google (other search engines are, apparently, available). I quickly found his webpage. The candle is indeed listed there, and it even has a name. It’s called the Rekindle. Which is quite a cool name, although it’s just possible Amazon might have an issue with it.

Well, Mr Shine might be a talented designer, but I fear his science is a tad shaky (assuming it’s a real design and not some kind of clever joke, in which case my apologies). This invention is the chemistry equivalent of a perpetual motion machine.

In case you’ve never heard of a perpetual motion machine, allow me to explain: it’s a hypothetical machine that continues indefinitely without any source of energy. If you just think about it for a moment you quickly realise that such a thing can’t be possible, because if it were half the world wouldn’t be squabbling over ever-decreasing oil supplies.

It doesn’t, and cannot, work because you can’t create or destroy energy (that’s the first law of thermodynamics. The second law is that we don’t talk about the first law. Perpetual motion machines violate that one too). If a machine is doing work, it will always lose some energy to its surroundings, due to friction and so on. In short, machines always produce less energy than you have to put in to start with.

candle-flame-1-ajhdNow Einstein, who was a terribly clever chap (and jolly good at Maths whilst at school despite the apocryphal story) came up with the famous equation: E=mc2, which rather elegantly links energy with matter. Thus, laws that apply to energy also apply to matter. If you can’t create or destroy energy, you can’t create or destroy matter, either. You can change it from one form to another, and under certain circumstances matter can be converted into energy, but you can’t actually create or destroy it. This is why your chemistry teacher made you balance all those flipping equations at school. It’s also why magic doesn’t work in real life (sorry Harry).

What has this got to do with candles? Well, what is the energy source in a candle? There has to be one, it’s producing heat and light. Here’s a clue: it’s not, as many people think, the wick.

No, it’s the wax. Depending on the source, waxes are basically hydrocarbons. Some of them have a bit of oxygen thrown into the mix as well, but essentially the equation is:

wax + oxygen –> carbon dioxide + water

So, you see, although Mr Shine’s design is interesting, the photos are I’m afraid rather misleading. Although a bit of wax might drip down the sides of a candle as you use it, if you burn it right down there definitely won’t be enough left to fill the container Benjamin Shine has shown filling up in the bottom section of his candle stick. You can’t have your cake and eat it, and you can’t have your candle and burn it too. 

“Oh ye seekers after perpetual motion, how many vain chimeras have you pursued? Go and take your place with the alchemists.”
         — Leonardo da Vinci, 1494

2 thoughts on “Perpetual motion in chemistry?

  1. I’d say the only way the original candle could do a reasonable job at filling up the drippings holder is if it’s a *very* drippy candle. That means the original candle will burn down much faster than a less drippy candle.

    You’ll still only get one candle’s worth of light out of it, but it’ll look nifty.


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