Question

1. can ice be melted merely by applying pressure? how about dry ice? Explain your answers.
2. explain how the solid liquid line in the phase diagram of water differs in character from the solid liquid line in the phase diagrams of most other substances such as CO2.
3. which phase of a substance (gas, liquid or soild) is most likely to be the stable phase:(A) at low temperature and high presumes (b)at high temperature and low pressure?
4. at what temperature and pressures does a substance behave as a supercritical fluid?
5. explain why a needle floats on the surface of water but sinks in a container of methanol?
6. explain why the plumbing in a house may burst If the temperature in the house drops below O°C?
7. a hot needle sinks when placed on the surface of cold water but a cold needle floats why?
8.what kind of intermoloccular force must be overcome as (a) soild CO2 sublime (b) CHC13 boils (c) ice melts?

Answer 1

1) Unlike most subtances Ice is less dense that water. If you apply pressure in Ice you are in fact promoting a reduction in volume, the only way to do this is water become liquid. Dry Ice fallow the normal behavior, apply pressure over it favours the solid state.

2) As it was explained above the solid liquid line in water has a negative slop means that increasing pressure at a given temperature favours the liquid phase contrary to Dry Ice that favour the solid phase with increase of pressure.

3) a) solid phase 3b) gas phase

4) At temperatures and pressures above the critical temperature and critical pressure.

5) because the water has a higher superficial tension that metanol, in this way water seems to form a film in the surface of it.

6) Because water in solid state occupies a major volume that in liquid state. That can broke the plumbing.

7) The hot needle transmits heat to their surroundings, heating the water, disturbing the molecular forces at the surface, canceling the surface tension forces that hold it floating.

8) a) dipole-dipole b)van der waals c) hydrogen bonds