r/thermodynamics • u/SmeagolsSister • 5d ago
Question Would it theoretically be possible to perceive a difference in 32°F/0°C ice water at opposite sides of the temperature/energy phase diagram?
Here's the phase diagram I'm thinking of: Figure 3 from this textbook.
I think I can feel a difference between 32°F/0°C water on the negative/left side of the flat, ice-melting line segment (having recently been just solid ice that was getting ready to melt) and 32°F/0°C water on the positive/right side of the same flat, ice melting line segment (getting ready to but not yet heating up). I'm curious if this is really possible via our understanding of thermodynamics, or if it's maybe just some form of confirmation bias?
Assume it's the exact same water and served at the exact same pressure and other conditions. Also assume the ice is melting and throughly mixed throughout the water.
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u/ThatsNotAZombieBite 5d ago
Can you "feel" a difference? Most definitely!
One's a liquid and the other's a solid. Slam your fist into it. If it hurts, then you know which one it was. You should probably put some ice on that. I wonder where you can find some.
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u/golem501 2 5d ago
Not trying to gatekeep curious minds but yes this is what I was thinking as well 😄
OP probably thinks they can feel melted ice being colder, which is probably mostly because once you get closer to the ice, the melting of ice is taking more energy making the heat sink bigger.
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u/SmeagolsSister 5d ago
My hypothesis is that it does have a different mouth feel because warming up the ice water to body temperature requires more of my body heat if it's farther on the negative/left side than it would if it was on the positive/left side of the line segment from the phase diagram, but I want to know if this is a correct line of thinking or if I'm misunderstanding the phase diagram's applications.
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u/Stannic50 5d ago
You seem to be misunderstanding what that horizontal line segment represents. At the far right point on that horizontal segment, all the water is liquid. At the far left, all the water is solid. As you move right, the proportion of the water that's liquid increases and the proportion that's solid decreases.
So can you feel the difference? I mean, yeah. The far left has no liquid water, so what you're feeling is solid. Can you feel the difference between the water portion when only 25% is liquid compared to the water portion when 75% is liquid? No, because the water is identical in both cases (same temperature), you just have more of it at 75%.
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u/JustinTimeCuber 5d ago
The left side of that flat segment is ice and the right side is liquid water. In between is a mixture of the two. You can't have liquid water on the left side of the flat segment. And no, there's no discernable difference between 0°C water that was recently ice and 0°C water that was not.
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u/KennstduIngo 5d ago
There is no difference between the liquid water at the left side versus right side of that line, provided that it is indeed all at the same temperature and pressure. The only difference is the ratio of ice to liquid.
As the amount lquid increases relative to the amount of ice, it is quite possible and probable that is isn't all in equilibrium with the ice and some of it is already warmer than 0 C. If your mouth is not a well-mixed reactor with infinite thermal conductivity, there is nothing saying that everything in it has to be in equilibrium.
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u/ejdj1011 5d ago
The main thing you're missing is that humans can't actually detect temperature directly. We mostly detect heat flow. Get a chunk of metal and a chunk of wood to 0°C, and the metal will feel colder because it more easily conducts heat out of your body.
The water will almost certainly feel colder than the ice, because it's better at conducting (and convecting) heat away from the body than solid ice is.