how is it that different substances can burn at different temperatures despite all being able to be ignited by the same temp match?
In: Chemistry
Ignition and combustion are two different things entirely.
Magnesium shavings burn incredibly hot up to 3,100 degrees Celsius. But they can be ignited at a temperature around 630-640 degrees Celsius. And it will spontaneously combust at 883 degrees Celsius.
Ignition is setting a substance on fire.
Combustion is that substance burning.
For a lot of substances, the ignition temperature is considerably lower than the combustion temperature.
You can think ignition like giving a ball a gentle push so that it starts rolling down a hill and releasing the energy it had but couldn’t release without the push. The ignition only starts the process. Match has more than enough “push” to ignite many familiar substances.
The temperature of the flame just depends on the amount of energy released, how much stuff that amount of energy heats and properties of the stuff. Different substances release different amounts of heat when burned, require different amounts of oxygen (so some flames have more air compared to fuel and some less) and can store more heat per unit of temperature. All these things relate to the various different chemical bonds between the atoms you burn. Some bonds are stronger and some weaker.
The ignition temperature is not the same for different substances. The ignition temperature is basically how big of a “push” different molecules need to start a reaction. The match is just very hot allowing it to light most substances
The temperature at which substances burn depends on various factors. But basically it’s an energy balance. A fire losses heat from various sources like convection and radiation, the higher temperature the more energy loss. A fire gains energy from the combustion of the fuel, the amount of energy from that depends on how much is being burnt, and how much energy is gained from the reaction. How much is being burnt is often limited by how much oxygen is available. The energy from the reaction depends on the fuel you can find that for different fuels by searching “heat of reaction”.
The temperature at which something burns, is the equilibrium where the heat out = heat generated.
So burning in a simple sense is material reacting with oxygen and releasing heat. The heat from that reaction causes more material to heat up and react with oxygen, creating a chain reaction that keeps it burning.
The more reactions with oxygen there are the hotter it gets, so from that first reaction it can become much hotter than the first reaction that started it burning if there is enough oxygen.
That’s why things have different “ignition temperature” (the temperature it starts burning) and “burn temperature” (the temperature it can reach burning in air).
Also if you introduce more oxygen it increases the temperature of a fire, that’s why blowing on a fire makes it burn hotter (unless it’s a small flame and you blow hard enough to blow it out).
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