Naked Science Forum

General Science => General Science => Topic started by: Mariana on 14/02/2019 13:52:11

Title: Why does ice melt?
Post by: Mariana on 14/02/2019 13:52:11

Kaitlyn wants to know:

Why does ice melt?

Can you help?

Title: Re: Why does ice melt?
Post by: Janus on 14/02/2019 16:28:49

Ice is a solid.  This means that the bonds between the molecules hold them in, for the most part, in fixed positions relative to each other.  They do have a small amount of freedom of movement, in that they " jiggle" a bit around these positions.  The jiggling is the result of the Energy due to the temperature of the Ice.  Temperature is a measure of the average kinetic energy of the individual molecules. 
The higher the temperature of the Ice, the greater the KE of the molecules and the more they "jiggle".  When the temp is high enough, the KE of the molecules becomes too great for the bonds to hold them in place (though not enough for the molecules to completely break free of each other),  and the molecule start to "slide" around each other, and Ice becomes a liquid. Iincrease the temp even more and the molecules can't even hold each other close, and they become completely free agents. The water turns into a gas).

Title: Re: Why does ice melt?
Post by: Petrochemicals on 15/02/2019 02:53:29

Ice forms at different temperatures under different pressures. Lower the pressure and the bond do not form until a lower temperature, super cooled water lower than 0C is present in the lower pressure upper atmosphere due to the energy in the water being more than the force it is experiencing.

Title: Re: Why does ice melt?
Post by: chiralSPO on 15/02/2019 03:10:58

Quote from: Petrochemicals on 15/02/2019 02:53:29

Ice forms at different temperatures under different pressures. Lower the pressure and the bond do not form until a lower temperature, super cooled water lower than 0C is present in the lower pressure upper atmosphere due to the energy in the water being more than the force it is experiencing.

I believe you have that backwards--water is an example of a substance that has a higher freezing point at lower pressures (attributed to the lower density of the solid as compared to the liquid). At sufficiently low pressures, the liquid is completely unstable, and only solid and gaseous phases are left to interconvert (by sublimation and deposition).

Title: Re: Why does ice melt?
Post by: Petrochemicals on 16/02/2019 03:47:06

Quote from: chiralSPO on 15/02/2019 03:10:58

Quote from: Petrochemicals on 15/02/2019 02:53:29

Ice forms at different temperatures under different pressures. Lower the pressure and the bond do not form until a lower temperature, super cooled water lower than 0C is present in the lower pressure upper atmosphere due to the energy in the water being more than the force it is experiencing.

I believe you have that backwards--water is an example of a substance that has a higher freezing point at lower pressures (attributed to the lower density of the solid as compared to the liquid). At sufficiently low pressures, the liquid is completely unstable, and only solid and gaseous phases are left to interconvert (by sublimation and deposition).

Thanks for that, i was under the impression it was because of the pressure.Funny stuff though water, the strange density.