“When ice is on fire, does the ice melt?”
It was one of those questions, the random sort of question a five-year-old (he just turned six last week, but he was five when he asked it) will ask. I don’t have any idea what prompted the question, or where it came from. But, the more I thought about it, the more interesting it sounded.
Can ice burn?
Well, it depends on what you mean by ‘ice’ and by ‘burn’. Here’s how Merriam-Webster defines it:
Full Definition of ice
- frozen water; a sheet or stretch of ice
- a substance resembling ice; especially : the solid state of a substance usually found as a gas or liquid <ammonia ice in the rings of Saturn
- a state of coldness (as from formality or reserve)
- a frozen dessert containing a flavoring (as fruit juice); especially : one containing no milk or cream; British : a serving of ice cream
- slang : diamonds; broadly : jewelry
- an undercover premium paid to a theater employee for choice theater tickets
- methamphetamine in the form of crystals of its hydrochloride salt C10H15N‧HCI when used illicitly for smoking —called also crystal, crystal meth
For these purposes, we’ll stick with the first two definitions. ‘Frozen water’ and ‘the solid state of a substance usually found as gas or liquid’.
Burning, more properly called a combustion reaction, is a little more complicated. There’s an entire subfield of chemistry called thermochemistry that deals with burning (or, more properly, the energy release from a combustion reaction). In general, though, you need a compound to combust and an oxidant to react with the combusting compound, and some energy to get it started. The oxidant and the combusting compound then combine in a chemical reaction to produce one or more new compounds, and since the reaction is exothermic the process of making the new compound(s) generates more energy than it gives off.
Yes, that does mean that once you get a combustion reaction started it will continue as long as it has combustable compounds and oxidants. That’s why fire spreads.
So, can ice burn?
Water does not burn particularly well, because it’s already a product of a combustion reaction. Burning just about anything with hydrogen produces water. Burning hydrocarbon (sugar, wood, meat, alcohol, whatever) produces carbon dioxide and water and heat, burning hydrogen generates water and heat, burning acetylene gas forms carbon dioxide and water, and so on. Because it is the product of a combustion reaction, water is already at a low energy. You’d have to add energy (breaking the chemical bonds between the hydrogen and oxygen) to burn it, and then you’re not actually burning the water. You’re burning the hydrogen gas you released from the water.
Other ices can burn, however. Ethanol (a hydrocarbon) burns, and it freezes at -114 degrees Celsius (-173.2 degrees Fahrenheit). Gasoline (another hydrocarbon) certainly burns, and will freeze between -40 degrees and -60 degrees Celsius (-40 to -76 degrees Fahrenheit), depending on the exact properties of the substances in the gasoline. Acetone (nail polish remover) is another hydrocarbon, which freezes at -95 degrees Celsius (-139 degrees Fahrenheit) and which burns. Other liquids that burn also exist, obviously. And most of them require dangerously cold temperatures to freeze, and then will have fire. Use caution, lots of caution, if you actually plan to try this at home. And then, having exercised caution, you probably shouldn’t try this at home.
But, I really want burning water ice. For reasons.
Well, there’s a couple of different things you can do. The first is to put a layer of (water) ice cubes on top of a layer of calcium carbide. As the ice melts, the water reacts with the calcium carbide to produce hydrogen and acetylene gas, both of which will burn – old fashioned mining lamps actually used this reaction (something I learned when I went spelunking as a Boy Scout). The results look like this:
Another option is to pour alcohol on top of your ice, and light it up. The ice won’t burn, but there will be flames on the ice.
Regardless of which one of these you do, if you do one of them, please exercise caution. Lots of caution, because you’re playing with fire.
But… does the ice melt?
Yes. Because there is something hot near the ice, which will cause it to melt.