What happens to the wax when a candle burns?

We were looking at a candle that we have in our kitchen. And we we were confused as to why when you burn it, the wax seems to get less and less. If the wax is just melting, where does it go? Why does it not all just melt when you burn it and harden back up again when it isn’t burning? — MD, Charlottesville, VA

As the candle burns, its wax melts into a liquid, that liquid “wicks” up the wick (like water flowing up into a paper towel), and then the extreme heat of the flame vaporizes the wax (it is become gaseous wax). Once the wax is a gas, it burns in much the same way that natural gas burns — it reacts with oxygen in the air to become water and carbon dioxide. That reaction released chemical potential energy as thermal energy.

One important difference between a candle flame and a natural gas flame: whereas the flame of a well-adjusted natural gas burner emits very little light (a dim blue glow), the flame of a candle is quite visible. That’s because the wax vapor in a candle flame isn’t mixed well with air before it begins to burn. Instead of burning quickly and completely, as natural gas does in a burner that premixes the gas with air, the wax vapor in a candle flame burns gradually as it continues to mix with air. The partially burned wax forms tiny carbon particles. Those carbon particles are so hot that they glow yellow-hot — they emit thermal radiation. In other words, they are “incandescent”. It’s those glowing carbon particles that produce the candle’s yellowish light. Eventually the carbon particles burn away to carbon dioxide.

Does color affect baking speed?

If I were to heat up a brownie and a white piece of cake, would the brownie heat up faster by radiation transfer because of its darker color? — B

In principle, the brownie would heat up faster by radiation in a hot environment and cool off faster by radiation in a cold environment. A black object is better at both absorbing thermal radiation and emitting thermal radiation, so the brownie would soak up more thermal radiation in the hot environment and give off more thermal radiation in the cold environment.

In practice, however, most of the radiation involved in baking these desserts and letting them cool on a kitchen counter is in the infrared and it’s hard to tell just what color a brownie or cake is in the infrared. It’s likely that both are pretty dark when viewed in infrared light. Basically, even things that look white to your eye are often gray or black in the infrared. Thus I suspect that both the brownie and cake absorb most of the thermal radiation they receive while being baked and emit thermal radiation efficienty while they’re cooling on the counter.

Hydrogen and Energy – Fraud, PR, and Politics

There is a video circulating on the internet which purports to show an “inventor” who has a machine that burns water. Water is broken down into hydrogen and oxygen which is then burned to produce….more water! I maintain that the net energy produced would be about zero since energy must be expended to separate water into hydrogen and oxygen. Your comments please. — ST, Arizona

You have it exactly right. Water itself is burned hydrogen, and the energy required to separate water into hydrogen and oxygen is equal to the energy released when the hydrogen subsequently burns back into water. Energy in and energy out. Just as in bicycling, if you want to roll downhill, you have to pedal uphill first.

Anyone who claims to be able to extract useful energy through a process that starts with water and ends with water is a charlatan. Either they aren’t producing any useful energy or it’s coming from some other source. In these sorts of frauds, there is usually some electrical component that is supposedly needed to keep a minor part of the apparatus functioning. That component isn’t insignificant at all; it’s what actually keeps the entire apparatus functioning!

Hydrogen has such a mythical aura to it, but in the context of energy, it’s just another fuel. Actually, it’s more of any energy storage medium than a basic fuel. That’s because hydrogen doesn’t occur naturally on earth and can only be produced by consuming another form of energy. There is so much talk about “the hydrogen economy” and the notion that hydrogen will rescue us from our dependence on petroleum. Sadly, politicians who promote hydrogen as the energy panacea neither understand science nor respect those who do. Since it takes just as much energy to produce hydrogen from water as is released when that hydrogen burns back into water, hydrogen alone won’t save us.

As we grow progressively more desperate for useable energy, the amount of fraud and misinformation will only increase. There are only a few true sources for useable energy: solar energy (which includes wind power, hydropower, and biomass), fossil fuels (which include petroleum and coal), geothermal energy, and nuclear fuels. Hydrogen is not among them; it can be produced only at the expense of one of the others. Even ethanol, which is touted as an environmentally sound replacement for petroleum, has its problems; producing a gallon of ethanol can all too easily consume a gallon of petroleum.

Where energy is concerned, watch out for fraud, hype, PR, and politics. If we survive the coming energy and climate crises, it will be because we’ve learned to conserve energy and to obtain it primarily from solar and perhaps nuclear sources. It will also be because we’ve learned to set politics and self-interest aside long enough to make accurate analyses and sound decisions.