About state of matter and melting point

[songoku]

Homework Statement

Hi all

I have conceptual problems :
1. In cold countries, water in pipe lines freezes in winter season. Freezing causes volumetric expansion and may burst the pipes.
My question :why freezing causes volumetric expansion?


2. Mostly, substance increases their melting point when a pressure is applied in their solid state. Ice is an exception. Applying pressure to ice will lower its melting point.
My question : why when a pressure is applied to an object, the melting point will increase? And why this concept can't be applied to ice?

3. Why does ice has lower density compared to water?

Homework Equations

The Attempt at a Solution

1. I think freezing causes volumetric compression. I imagine the water freezes to ice and I think that the volume becomes smaller.

2. I don't have any ideas.

3. Ice is a solid and I think it should have stronger inter-molecular force compared to water. Stronger inter-molecular force means that it has higher density. But ice floats on water and it means that it has lower density. I don't understand.

Thanks

 

[ideasrule]

All of your questions are related to the structure of ice crystals. See http://www.iapws.org/faq1/freeze.htm for an explanation.

 

[songoku]

Hi ideasrule

Ah thank a lot for the link. I understand the first and third questions but the link doesn't explain about second question.

Thanks