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This question already has an answer here:

I would like to know what is the chemistry of cutting. For example, when we use a knife to cut through bread what exactly happens on a molecular level? Are ions formed, do long organic compounds (e.g. in cheese) break, or are just intermolecular interaction that seize to exist?

Thanks a lot in advance.

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marked as duplicate by Todd Minehardt, Jon Custer, bon, Klaus-Dieter Warzecha, ron Jul 18 '16 at 13:45

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It depends. Bread has moth small molecules (like 2-Acetyl-1-pyrroline). These molecules will just pushed aside by the blade. You have hydrogen bond network between water molecules. You break those. Bread has large polymers like starch. Knife breaks those.

A cleaner system to study is a polyethylene. You can freeze it in N2, break under inert atmosphere and study by EPR spectroscopy. You will find free radicals at the breaking point. This is because it costs less energy to break a bond then to move one molecule relative to others.

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Essentially, what you are doing with an everyday knife is wedging your way through the substance. You are pushing aside the particles within the substance. In this instance, bread; you are pushing apart the different particles, requiring you to break the inter molecular forces that held them together.

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