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Is it possible to freeze water if it is directly exposed to $-1\ \mathrm{^\circ C}$ and not $0\ \mathrm{^\circ C}$? Is freezing point the minimum temperature at which a substance can be froze?

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    $\begingroup$ Yes, it will start cooling down to -1, going though 0 and then freezing at 0. You can in theory supercool water, but that's another story. The freezing point is the temperature that a substance is frozen below it. $\endgroup$ – Gimelist Aug 15 '16 at 6:40
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Yes it is possible. Even if you expose water to an object at −50 °C, it will freeze. This is due to the fact that when you place two objects, heat transfer occurs. It is not a spontaneous process, it will take time for water to release heat and cool and eventually freeze.

Freezing point is merely the degree temperature at which a substance changes from liquid to solid phase. It is the temperature at which the substance will freeze.

Hope this helps.

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    $\begingroup$ I down voted this. To me you missed key points. "Heat" transfer takes place from hot to cold. Liquid water would decrease in temperature to 0 C at which point the liquid water would start to freeze. Once all the water has frozen to ice, then the ice would cool to -1 C. $\endgroup$ – MaxW Aug 15 '16 at 18:01
  • $\begingroup$ Yes, I've missed all that...thanks @MaxW, for telling me what's wrong before downvoting, which for me is seldom seen. $\endgroup$ – Akshar Gandhi Aug 18 '16 at 6:05
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At atmospheric pressure it is possible to supercool water down to almost -50°C before it freezes. The water has to be very pure and not in contact with surfaces which will act as nucleation sites but supercooled water droplets are common in clouds and pose a danger to aircraft (ice formation on the wings). 0°C is the "freezing point" because it is the temperature that most fairly pure water will freeze at and the point at which ice will melt. If you slowly apply heat to ice (Ice 1h, hexagonal ice, is the stable form of ice at ~0°C and 1 atm) starting below 0°C, temperature rises until 0° when temperature will stop rising until the ice is melted (phase change from solid to liquid) after the ice is melted, temperature will begin to rise again (the rate of rise per energy input is known as its specific heat capacity, Cp, and that rate is different for liquid and solid water.)

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It is possible by pressure too! Above $10~\mathrm{MPa}$ melting point of water decreases. At $209.9~\mathrm{MPa}$ melting point become $-21.9°\mathrm{C}$. For more information, see this page.

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