Is Chalk Flammable? (A definitive guide)

In this article we will discuss the following: “Is Chalk Flammable”, and other important questions about the nature of chalk.

Is Chalk Flammable?

No. Chalk can’t burn outside industrial conditions. But even in these conditions, no fire rises from the attempt of burning because when chalk burns, it actually absorbs energy instead of releasing it in the form of fire.

What is chalk?

Chalk is a rock. It’s a porous, white, and soft carbonate rock, it comes from the mineral calcite.

Chalk is a type of limestone, approximately made of 97% of calcium carbonate (CaCO3). Like most rocks, its composition is entirely made of inorganic compounds.

Calcium carbonate is the same mineral that composes the shells of all kinds of crustaceous.

Where does it come from?

Chalk was formed during the Cretaceous era, between 65 and 99 million years ago. It was formed at the bottom of the sea, during an arid period of time, by the constant compression of microscopic organisms on the seafloor

The mineral deposit was so common during the Cretaceous Period that its name was given after it. Creta, in Latin, means chalk.

Can chalk burn?

Although simple, this question requires a little science to be answered. 

First, we must understand what fire is and how something catches fire, and then analyze what chalk is made of. In the end, you will realize that chalk could burn, but it won’t do it easily.

But even if it happened, chalk wouldn’t be a fire hazard.

What is fire?

Fire is a chemical reaction where a source of fuel reacts with the air’s oxygen, generating heat and other byproducts.

Usually, fuel is a hydrocarbon or another similar organic compound.

In simple terms: a fire happens when oxygen approaches the carbon, and carbon decides to leave its molecules to start a new one. From this marriage, a strong bond is formed. This new molecule is carbon dioxide, usually.

The main reason why we use petroleum elements as fuel is that once we put some fire on them, they start breaking apart and give us a lot of energy in the form of heat.

This happens because hydrocarbon molecules have a lot of chemical energy within them.

Chemistry is all about energy. The only thing molecules “pursue” in their “life” is stability. They rarely care about anything else. 

One of the ways to achieve stability is by simply losing energy, which is exactly what fuels do when they burn. Burning is just a consequence of the chemical reaction that takes place.

But let’s return to our goal here. What is fire?

CH4 + 2 O2 → CO2 + 2 H2O + energy(fire)

This is how a combustion reaction looks like. The CH4 is the simpler hydrocarbon molecule possible. O2 is the oxygen molecule. The arrow always points towards the result.

Fire is what we can see from the burning of fuel. Combustion commonly generates carbon dioxide (CO2), water(H2O), heat, and light, among other less popular compounds. 

Whenever a fire takes place, it is because this chemical reaction is undergoing. If the reaction stops, fire ceases. But the fire can only continue if it can keep having fuel, oxygen, and heat added to it.

Since the chemical reaction is made with oxygen there’s also another name we can give to it: oxidation. 

Therefore, combustion is a specific kind of oxidation where a fuel gets transformed into simpler compounds, generating energy. That’s what fire is.

What is chalk again?

In essence, chalk is the molecule CaCO3. This means: in every molecule, there is one atom of calcium (Ca), one carbon (C), and three oxygens (O).

Even though calcium carbonate has carbon molecules, it is not an organic compound. This means that it can’t catch fire the way we explained above.

Organic compounds are mainly constituted of carbon and hydrogen. When they burn, the oxygen atoms enter the fuel molecules and steal the carbon. The hydrogen atoms also react with oxygen, giving birth to water.

But inorganic compounds don’t have hydrogens. Also, unlike organic compounds, there’s no guarantee that inorganic compounds would want to bargain with oxygen because they already have low energy.

If we try to burn chalk, the oxygen will not easily steal the carbon from it because it’s a bad trade for both.

But what if we do burn chalk?

If we force to burn CaCO3, at some point oxygen would react, but only after reaching really high temperatures (about 1000ºC/ 1832ºF). The chemical reaction would be the following:

CaCO3 → CaO + CO2

You can see that carbon dioxide was formed, but no water. Also, why isn’t O2 on the left side of this equation?

As we said, this is not an usual burning. The oxygen used in the reaction comes from the CaCO3 itself, not the air. 

Can we even consider this a combustion? Well, I’m not sure. But this is only a formality. In fact, this reaction is very important worldwide, and is named “calcination”.

The big question is: Does chalk catch fire/generate heat?

Well, no. If we apply a lot of heat on chalk, it won’t generate more heat. The calcination reaction does not generate heat on its own, but quite the opposite.

So here’s the thing: Not only chalk can’t burn, but if we try to ignite it by force, the chemical reaction that takes place doesn’t produce fire. It even steals some heat from the surroundings.

Safety Data Sheets

Most products that are commercialized require the writing of a document that contains all the useful safety information regarding the product.

We now present three examples of Chalk materials. None of them is flammable as we expected, and the other risks involved are minimal. Feel free to check the links if you need further safety explanations.

  • Product name: Chalk
    Company name: WuXi XinKe Tools Manufacture Co.,Ltd
    Flammability: none
    Link
  • Product name: French Chalk Poder
    Company name: Oxford
    Flammability: none
    Link
  • Product name: Strait-Line Marking Chalk 7 (Red)
    Company name: American Tool
    Flammability: none
    Link

Conclusion

Chalk is an inorganic structure that can’t burn easily. The chemical reaction that happens if we try to burn chalk doesn’t produce heat on its own, so no fire would arise from it. 

But even if this reaction did produce fire, temperatures around 1000ºC would be needed to do so, which requires a really big fire. 

Frequently Asked Questions (FAQS): Is Chalk Flammable?

is chalk edible?

Well, it may irritate your stomach if consumed dried. In fact, calcium carbonate is used to compose some medicines, especially antacids.

Although, eating raw chalk could lead to the following problems: tooth damage, digestive problems, constipation, lead poisoning, parasites, and feeding disorders.

Will chalk dissolve in water?

Chalk has low solubility in water. On average, only 0.015 grams dissolve in one liter of pure water (0.033lbs in 33.8 ounces).

is chalk a compound?

More or less. Chalk is a rock that’s almost entirely made of the molecule CaCO3, which is a chemical compound. It’s made of 3 different atoms.

Citations

Pyne, Stephen J. Fire: a brief history. University of Washington Press, 2019.

https://en.wikipedia.org/wiki/Chalk
https://en.wikipedia.org/wiki/Carbonate_rock
https://en.wikipedia.org/wiki/Calcination
https://en.wikipedia.org/wiki/Combustion

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