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Q & A: Why does a boiled egg harden?

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Most recent answer: 08/24/2012
Q:
As we were all familiar about entropy .As the temperature increases entropy also increases, but when we increase the temperature of an egg, the egg starts changing its state from liquid to solid form.then the entropy will decreases.if it is so then what about 2nd law of thermodynamics.plz explain the phenomema
- MUMTAZ AHMAD (age 21)
KARGIL LADAKH ,J&K ,INDIA
A:
There's no absolute law that solid things have lower entropy than liquid things. In fact, in one very well studied clean case, He3, the liquid freezes to a solid on heating. The reasons are subtle and quantum mechanical, but well understood. The solid has higher spin entropy.

Now for eggs: The hardened egg isn't really a solid in the physics sense. It's more like a glass. Here's what happens to the egg whites as they cook. When they're cold, the chain-like protein (allbumen) molecules are folded up into little balls. There's a specific way each folds. That arrangement has relatively low entropy. The little balls can roll past each other, so the whole thing is liquid. On heating, the molecules unfold and start flopping around. As you might guess, this has higher entropy. Once unfolded, the molecules get tangled up with each other and flow less easily than when they were little balls. When they then cool down they stay tangled up and really get stuck in a fairly rigid rubbery cluster.

The key general lesson to take from this is that entropy is a genuine physical quantity that has to be calculated based on a full microscopic picture. Vague impressions from the outside about what entropy might be doing are often incorrect.

Mike W.



(published on 08/24/2012)

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