Ice-Water equilibrium

intothewild SG

Happy New Year ppl.

I have a question about LCP and Ice-Water equilibrium, which I tried to google around but still didnt manange to find my answer.

H20(l) (density = 1kgdm-3) <---> H20(s) (density = 0.92kgdm-3)

Explain why application of pressure to ice at 0 degree Celsius makes it melt. Why do most other solids not show the same behaviour?

My initial analysis:
At first by using LCP, when pressure is applied to ice, the system will try to counteract the change by reducing pressure. To reduce pressure, the system will favor an increase in volume. Ice has a larger volume as compared to water for the same weight.
So why would ice melt if pressure is applied?

Yet in reality, I am aware that ice will melt which explains why and how ice-skaters are able to ice-skate; and why in Winter, boots get stickier as one treads on ice, and hence become dangerous to walk on.

I read in some sites that increasing pressure will cause the melting point of water to decrease, hence, ice melts. But how is that possible?

I think water is such a useful yet bizzare molecule/substance.

Thanks for anyone who can enlighten me.

skythewood SG

when pressure change, melting point change. google on that.

Eyelessz SG

My initial analysis:
At first by using LCP, when pressure is applied to ice, the system will try to counteract the change by reducing pressure.

> This is correct. Now the question gave you density, so make use of that.

According to PV = nRT equation,

when you sub in density, u get : PM/D = nRT

This means density is inversely proportionate to Pressure.

When the system wants to reduce pressure, it has to increase it density, According to LCP, the system will favour the backwards reaction towards an increase in density. Therefore ice would melt when pressure is applied

eagle SG

erm....

PV = nRT is an ideal gas equation, so you can't use it to explain solid/liquid states.

Anyway, to TS, this is what I think...
Ice/Water is at its densest at 4 degrees celsius in liquid form. When we apply pressure, we are in fact forcing the substance that we are applying pressure on to take up less space, i.e. take up less volume, or in other words, become denser since mass remains the same.

Since H2O is at its densest at 4 degrees celsius, high pressure will 'force' the H2O ice to move into its densest state in that liquid form.

Btw, what does LCP stand for?

UltimaOnline SG

Btw, what does LCP stand for?

Le Chatelier's Principle.

>>> Explain why application of pressure to ice at 0 degree Celsius makes it melt. Why do most other solids not show the same behaviour? <<<

As to why ice melts under pressure...

All the explanations offered so far are correct, but here is how I would put it :

Water in solid state exists as a fixed crystalline lattice structure, thanks to hydrogen bonds between water molecules that result in fixed (and precise) geometries with fixed (and precise) hydrogen bond lengths and intermolecular distances. Putting pressure would disrupt such a fixed crystalline lattice structure (that we perceive as a solid state), and hence the chaotic disorderly structure of water that results, is what we perceive as the liquid state.

16/f/lonely SG

Wah....reminds me of the triple point of water. Where ice, water and vapour coexists in equilibrium.

UltimaOnline SG

Wah....reminds me of the triple point of water. Where ice, water and vapour coexists in equilibrium.

Very good.

http://en.wikipedia.org/wiki/Triple_point

So where are you applying to study next, after you get your results, Miss 16 yrs old?

16/f/lonely SG

Very good.

http://en.wikipedia.org/wiki/Triple_point

So where are you applying to study next, after you get your results, Miss 16 yrs old?

Laughing

I thought you don't believe that I really am 16?

I look forward to majoring in economics actually.....am going to ORD in exactly 1 month from today.

16/f/lonely SG

Happy New Year ppl.

I have a question about LCP and Ice-Water equilibrium, which I tried to google around but still didnt manange to find my answer.

H20(l) (density = 1kgdm-3) <---> H20(s) (density = 0.92kgdm-3)

Explain why application of pressure to ice at 0 degree Celsius makes it melt. Why do most other solids not show the same behaviour?

Put it this way. Increasing the pressure exerted on a substance deforms its structure, at the same time increasing the energy transmitted to the substance deforming the structure further. This pushes down the melting point as it becomes easier for the molecules to break free from their rigid positions.

Adding impurities to water will also lower the melting point as the impurities will intefere with the hydrogen bonds formed between the water molecules.

UltimaOnline SG

Laughing

I thought you don't believe that I really am 16?

I look forward to majoring in economics actually.....am going to ORD in exactly 1 month from today.

With your penchant for misdirection, particularly in regard to your sexuality, you wouldn't happen to be in the SAF MDC, would you?

Happy ORD!