Combustion = Exothermic

[Ian_Lee_1E]

Hello, I am a little confused on why combustion is exothermic.

I thought combustion uses heat to break bonds so it was going to be endothermic.

What is the explanation to why they are exothermic reactions?

[Jeffrey Hablewitz 2I]

You are right that breaking to bonds of the reactants is an endothermic process. But combustion is always exothermic because the formation of O-H bonds in H₂O and C=O bonds in CO₂ always releases more energy than required to break the O=O bonds in O₂ and the C-C/C-H bonds in the material being combusted.

[Sharon Kim 2A]

Yes, you are breaking bonds in the reactions but you are still forming bonds to make CO2 and H2O. I'm thinking that since there are both processes of forming bonds and breaking bonds, the energy released from forming bonds is much larger than the energy needed to break the bonds.

[Tanya Bearson 2K]

One way you can conceptualize this is that combustion reactions will be hot due to the fact that something is being burned. This heat is coming from the large amount of thermal energy released. This is a good indication that it is an exothermic reaction.

[Melis Kasaba 2B]

Combustion is always exothermic because it's an oxidation reaction that produces heat. All chemical reactions involve breaking bonds and then making new ones, so if the energy released by the new bonds is greater than the energy needed to break the original bonds.

[Kayle Lim 2C]

Sometimes I get confused with the definitions of exothermic and endothermic reactions too, so I can see why you would think this! Combustion always releases more energy than it uses which results in the production of heat. An example of combustion would be a car using gasoline. CO2 is produced and releases energy which warms the surroundings. This would be an exothermic reaction taking place. I hope this helps to visualize the relationship with combustion being an exothermic reaction!

[Mingzi Yang 1E]

I have the same question too! All the explanations clarified my question!

[alexandralopez 3F]

Yes thats right! But, the energy released from forming bonds is much larger than the energy needed to break the bonds which is what makes it exothermic

[Annie Liang 3D]

Combustion is exothermic because the overall the reaction is releasing energy. Even though you are putting in energy to break the bonds, there is a larger release in energy.

[Vivian_Le_1L]

Yes, combustion does require energy to break bonds, however, the energy released to form the new bonds is greater than the energy taken in. Thus, the reaction is overall releasing energy and exothermic.

[Alexandra Salata 2L]

It’s an oxidation reaction that releases heat. But relatively speaking, the energy released from forming bonds is larger than that of breaking bonds as well.

[Samir 3I]

Most of the time we see carbon-carbon and/or carbon-hydrogen bonds being broken (think hydrocarbons in gas, oil, and even wood) we know that combustion is occurring because these bonds are being broken releasing the large amounts of energy they "store" (making the reaction exothermic). The result of the reaction is H2O, CO2, and energy, another telltale sign that combustion is occurring.

[Shivani Kapur 2J]

The energy that is released from forming the bonds in the products is greater than the energy used to break the bonds in the reactants.

[jasmineculilap_3F]

It's exothermic because there are still bonds being formed that release more energy than the energy needed to break bonds.

[Astha Patel 2J]

When you form the bonds to make water and carbon dioxide, that releases more energy than it takes to break the bonds in the reactants. Also, think of combustion as producing heat, so you know that it's "releasing" heat, and would therefore be exothermic.

[Keshav Patel 14B 2B]

The way to look at combustion is by looking at the products and reactants. If the products don’t have bonds, then the products combusted and released heat to break their bonds.

[Jaden Kwon 3C]

Even though bonds are broken in combustion reactions, the energy released when forming bonds is higher than the energy required to break bonds which makes combustion exothermic. Another way to think about it is in real life where burning something makes the surroundings hot which means combustion is exothermic.

[Ansh Patel 2I]

Hi! You're correct in that combustion requires energy to break bonds, but the energy released when new bonds are formed is greater than the energy absorbed, making it exothermic.

[Jamie2002]

Combustion is exothermic because a water molecule is being formed. Formation of bonds releases energy, so it is exothermic.

[Hasan Mirza 3F]

The bonds being formed release more heat than the bonds broken, but more generally think of a fire. As a fire burns heat is released into the surroundings and is obviously exothermic. Heat isn't a reactant, it is a product.

[Nicoli Peiris 1B]

Combustion is exothermic because the energy release when new bonds are formed is greater than the energy needed to break bonds in the reactants.

[Carly_Lipschitz_3H]

Combustion is exothermic because it produces heat. The energy released by the bonds exceeds the energy that was used to break the bonds, making the process exothermic.

[James_Hankee_1C]

Combustion produces heat so it is exothermic. The energy released is greater than the energy to form the bonds

[Gian Boco 2G]

While heat is required to break the bonds initially, the bonds formed release more energy than that initial amount of inputted energy, resulting in a net release of energy.