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Question:
We have been studying chemical and physical changes in 6th grade science class and we were wondering whether hard boiling an egg would be a chemical or a physical change? Thanks for a reply!



Replies:
You decide. Here's what's going on: the proteins in the fresh egg are in the shape of tight little balls. When you boil the egg, these proteins unravel ("denature"), like balls of yarn unraveling into loose skeins. The strands of protein then get all tangled up with one another, so much so that they are locked in place and can no longer move. They also lock into place the other liquid components of the egg, forming all together what's called a "gel" instead of the liquid you started off with. The gel acts like a soft, rubbery solid because of the network of protein strands holding it all together. It's certainly true that when the protein denatures some chemical bonds are broken, but the most important effect is the tangling up process.

The same thing happens when you boil your Jell-o, which is named that way because of course it's a gel. Other famous gels include contact lenses, slug slime -- I am NOT making this up -- and the stuff inside your eyeball.

Christopher Grayce



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