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Microscope: Fire vs lava

Mike

29 August, 2013

Welcome to Double Helix magazine’s Q&A section – Microscope. We take a close look at small questions full of big ideas.

Q: I want to know which is hotter, fire or lava? Or are they both the same?
Double Helix reader, Mical from New South Wales

Stylised image of an erupting volcano — Which is hotter – fire or lava?

Shaking is something you do when you’re feeling cold. But, it’s also what tiny particles do when they’re hot.

All atoms, big and small, bounce and jiggle about randomly. Heat describes how energy makes them move this way. On the other hand, temperature is a measurement of the amount of bounce and jiggle there is in bunches of atoms. So, which has bouncier particles – fire or lava? The answer might surprise you.

Fire is a chemical reaction caused by a fuel, such as wood, gas or oil, combining with oxygen. When the molecules of fuel recombine with oxygen, other chemicals, such as carbon dioxide and water, are formed. This swapping of atoms releases a lot of the fuel’s energy in the form of light and heat. The energy in this heat and light depends on the chemicals in the fuel and how quickly they combine with oxygen.

If the fire is a burning candle, parts of the flame can be as hot as 1400 °C! However, since the wick is small and thin, the hot area is tiny, so it doesn’t contain a lot of heat energy.

How does that compare with lava? Molten rock in the mantle under Earth’s crust is under a lot of pressure. Radioactive particles also knock the molten rock’s atoms around, making them hot. Close to Earth’s core, the mantle’s temperature can be as high as 4000 °C. But near the surface, the molten rock (or magma) is a lot cooler. In fact, as it spills out onto Earth’s surface as lava, the runny rock’s temperature is only a little lower than the hottest part of a candle flame: about 1200 °C. On the other hand, a big blob of lava contains many more bouncing particles than a small candle flame, so it has a lot more heat energy.

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Categories:

Earth and space sciences, Science

Tags:

Earth sciences, fire, heat, lava, magma, microscope, question, temperature

7 responses

Lola

21 November, 2019

Nice

Reply
Mr.Wu

7 January, 2020

We all know that fire is about 600-800 degrees Celsius, and lava was 700-1200 Celsius and of course lava would be hotter than fire. But my question is that will lava MELT fire? If those information was added, I think this is a good piece of information.

Thanks.

Reply
1. David
  
  8 January, 2020
  
  Hi Mr Wu,
  I don’t think fire can melt – it’s not a solid!
  
  Reply
Harry

24 June, 2020

So who is the hotter?

Reply
1. David
  
  24 June, 2020
  
  TLDR: The hot bit of a candle flame is usually hotter than lava coming out of a volcano. But lava is more dangerous to touch than a candle flame.
  
  Reply
George Purevdorj

11 December, 2020

By far one of the most stupid questions I have heard. Everybody knows that fire is the one that melts stuff. Not the one that gets melted. The temperature of the fire depends on its fuel. So quit blaming it for being so cold. If you replace wood with Dicyanoacetylene, the temperature of the fire will shoot up from a weak 1000 degrees to a Jesus-Christ-that’s-hot 4990 degrees celsius. Make the ozone as the oxidizer and boom! 5,730 °C. Lava is technically a fuel too. It’s just a liquid rock that is burning. You can see lava flowing and some parts of it are obviously on fire. And also, put some stones into a gas torch furnace. Wait for a little bit and then you have lava. You can never expect lava to be hotter than it is due to the fact that IT IS ACTUALLY A SUBSTANCE THAT JUST GOT MELTED. Which means it is not technically generating heat. It’s just conducting it. Fire on the other hand has no limits to how hot it can get as long as you have the right fuel. If you melt candle wax and touch it as soon as you take away the fire, you will actually burn your hand. The same goes for lava. It’s like a melting wax down there inside earth and when it comes out, it would temporarily still have it’s heat but will quickly lose it. Because unlike fire and just like a melted candle wax, it does not generate heat. Lava=Melted substances that are on a bigger scale.

Reply
Sanji2sickk

4 December, 2021

no way so Mr 3 > Akainu

Reply