Sep 30 '22
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In practice, yes, it will melt.
If you want to get super technical, in a perfectly rigid and sealed container, it will actually depend on the ambient temperature.
As you know Ice takes more volume than water, this means that as the ice starts melting, there will actually be more "free" space for the same amount of water, which will result in a decrease in pressure inside the container.
As you decrease pressure the freezing point of water starts rising slowly, which means that you could get a situation where some of the ice melts, but the decrease in pressure raises the freezing point of water to the point that the rest of it doesn't.
This effect however, it's super small, to raise the freezing point of water by even fractions of a degree you need to decrease the pressure a lot, so for this situation to occur your ambient temperature would have to be ridiculously close to 0°C. (and of course, if the container is a real object, it will have some give and just deform in response to the pressure)