# Entropy change in a boiling egg

Yesterday in a rather intuitive Q/A session, by a visiting researcher in my town, this question got my attention.What he said was that if you boil an egg, the entropy inside the egg would increase.Now common convention and logic dictates that the entropy will decrease(considering only the innards of the egg in the system), but this guy would not give up.He insisted on the contrary,and has given us time to think it out.

I don't know which SE site to referer to, for this question.Any migration of this question, if necessary would be helpful. Thanks!

• After the egg has cooled down and is in equilibrium with its environment? – user12029 Mar 10 '16 at 18:33
• You might say that, or rather that after it has hardened up – Abhinav Mar 10 '16 at 18:34
• Entropy always has a tendency to increase. Have fun "unboiling" an egg. The solidification is not of the same liquid that was originally present. Boiling results in a denaturing of protein which changes the chemical AND physical properties of the egg. – Jaywalker Mar 10 '16 at 18:56
• To add more to what @Jaywalker said, a denatured protein has many more degrees of freedom than a folded on, hence higher entropy. Take a look at this video for a graphical idea of why. When the proteins in an egg are denatured each protein is more free to flop around, but together they happen to form a solid. Many people associate solids with lower temperature and therefore lower entropy. This association holds for many systems, but not for eggs. – James Rowland Mar 10 '16 at 20:08
• @JamesRowland this should be an answer – nluigi Mar 11 '16 at 6:01

I’ve come across several claims that a (hard) boiled egg has greater entropy than an unboiled egg. None of them cite any peer-reviewed research to back up their claim. While it is possible that entropy increases when you boil an egg, it is also possible that it does not. It is even possible that it stays the same.

I did my own literature search to see if I could find any publication that answered the question. What I found left the question very much up in the air. So I contacted Greg Weiss, a scientist who has done research on a related topic: ‘unboiling’ an egg: https://www.livescience.com/49610-scientists-unboil-egg.html . Dr. Weiss was kind enough to discuss the topic with me via email.

Here’s the tl;dr summary: Whether a hard-boiled egg has greater entropy all boils down to the question of how structured are the assemblies found in aggregated ovalbumin. Furthermore, we can't just consider the assemblies found in the ovalbumin aggregate since we're talking about assemblies composed of all the types of protein in the overall albumen. (BTW, it's important to note that heated egg white doesn't just form any type of aggregate, it forms a gel, which presumably implies additional structure.)

For those who are interested in the details, here is the full email thread: https://docs.google.com/document/d/1Yt-usFLd3sm7MYpVTfwy3Yza6t3Ub6Q3lUZo7on5_wk/edit?usp=sharing

• "all boils down to" I see what you did there xD – pentane Apr 2 '18 at 0:17

An intuitive way of thinking about boiling an egg, is that you start a pool with a bunch of balls of yarn floating in it. Then when you heat the egg, it causes all the balls of yarn to unravel, and rather than a pool with some balls in it now it's a tangled mess of yarn. Before, each ball was free to move around as a unit, now each segment of each strand can wiggle around separately. This creates a whole lot more possible states and increases the entropy.

If you do an entropy balance on an egg as a closed system (Make it closed by sealing it if you have to), it looks like this: $$\frac Q{T_b} + \sigma = S_{\rm final} - S_{\rm initial}$$ where $T_b$ is the absolute temperature of the egg and sigma is the entropy production. Then adding heat to this system produces a positive $Q\over T_b$ entropy transport term into the egg. The entropy production (sigma) of this (or any) process is always positive, so the entropy of the egg increases as it is boiled and hardens. That is, of course, unless the egg gives off heat as it hardens. Then, if sigma is small enough, the egg's entropy could decrease. So it depends on whether or not the egg hardening process is endothermic or exothermic.

• Doesnt experience show (you need a heat source to boil an egg), that the process is endothermic? – lalala Apr 1 '18 at 20:51

I like the answer by Nick Gall, but I will be controversial here.

An egg while in boiling water is not a closed system, so anything goes.

A seed crystal growing in a solution is not a closed system, the crystal coming out has lower entropy than the solution, the extra going into the solution and the black body radiation ( counting microstates) of the system.

I can accept the hypothesis that the unraveling of the proteins while being boiled increases the entropy in the sub system, while the egg is still liquid. But then it solidifies. Solidity means a depletion in the degrees of freedom, of those strands, so also in the number of microstates available, which after taken out of the water as hard boiled will not change. (unless eaten).

I will say that as in the crystal, the only degrees of freedom are rotations and vibrations , so the entropy of the boiled egg is smaller than the entropy of a soft boiled egg, with all those protein strands waving around. Whether it is smaller than a raw egg, one has to experiment. My guess is since the strands are folded in the raw egg, but they have more degrees of freedom of moving in the liquid, higher than the solidified ones in the hard boiled, the entropy of the raw egg is higher than the hard boiled one. It is a guess, one has to measure, or at least to offer a detailed model, one way or the other, on why hardness of egg is different than hardness of crystal in entropy terms.

• As a student, I'm always overawed by the amazing thought process everyone here has. – Abhinav Jul 11 '19 at 6:58

If you instantly raise the temperature of an isolated egg from 30°C to 90°C it will naturally go from "uncooked state" to "boiled state" (through chemical reactions) after some time. Since we know from the second law of thermodynamics that entropy always increases, it seems rather trivial that the entropy of the second state (ie. boiled), has a higher entropy. There's no need to get into details of internal degrees of freedom and such imho... what am I missing?

• The idea that the solidification of the cooked egg seems rather counterintuitive when you think about increasing entropy in general(takw for instance heated water vaporizing and moving more violently on a molecular level, with added volume etc.) is the crux. It does seem trivial if one simply looks at the thermodynamics law associated doesn't it? – Abhinav Jul 11 '19 at 6:56

So it seems to me that the variables which determine an increase or decrease in entropy are:

1) state of egg pre-boiling; ie temperature of egg 2) entry method: directly into boiling water or boiled with water (gradual increase in temp) 3) amount of water: fully submerged or is it iceberging it 4) population of boiling eggs: wouldn't more eggs take longer to boil, however neglible the measurement, as the heat is dispersed into different systems? 5) length of time in boiling water. Some like it soft, some like it hard. (Some like the yolk gray...) 6) cooling method: sit in pan, air cool, directly into refrigeration, bowl of cool water (just fill bowl once or continuous stream until water remains cool), bowl then into fridge, bowl of ice water then into fridge, how long it stays in the fridge...

While personal taste determines what to enter into these functions, what other variables could be operating? What's the perfect way to boil an egg?

Observation: the eggs that are notoriously frustrating to peel appear to have multiple layers of cooked white. Could it be that the proteins organize themselves into the hard or soft variety at set intervals of time and temperature? If that specific structure is responsive to a very specific temperature and the temperature of a boiling egg increases radiating inward (at this point I'm tempted to consider the position and size of the yolk within but perhaps that becomes comically granular) it makes sense that layers would form.

Could it be argued that entropy within an egg whilst boiling both increases and decreases as there are multiple systems interacting? Maybe thehe proteins folding themselves into a specific pattern is an increase while the effects that has on the next system up appear as a decrease?

• That's a great observation! But I'm in doubt, that if we are considering heat radiating inwards, what reason could we possibly have to think that structure formation wouldn't ultimately tend towards the same end structure, no matter what layer it is, and as such could we just conclude that the layer formation is simply an intermediate stage(which it no doubt is) and that the proverbial push-pull of entropy between consecutive layers(aka interacting systems) that you suggest still has the same net change which tends towards an increment? – Abhinav Jul 11 '19 at 7:46

On boiling an egg entropy increases as due to denaturation the helical structure of protein become more complicated and random coiled structure.

You would have thought that on boiling the liquid protein (albumin) gets solidifies and thus entropy decreases. But that's not the case, we need to look the condition before and after boiling, i,e after boiling the structure gets complicated due to formation of different H bonds.

After boiling a raw egg, the entropy increases because we know that entropy=degree of randomness. Due to the change in temp, but we always thought on the conversion of liquid to solid as raw egg get heated the albumin get converted into a solid due to the hydrogen bonding but here temp get changed from initial to final temperature inside the egg.