Question on Thermal Physics.

[KoalaPowa]

Not homework, just need some help with explaining the effect of the following 2 things on the melting point/freezing point and boiling point of water;

1. Pressure is increased
2. Impurities are added

If possible, can the explanations be as explicit as possible?? I have really no idea how to work on it and any help is greatly appreciated. Thanks!

 

[wbandersonjr]

What do you think happens?

Obviously boiling, freezing, melting points are linked to a specific temperature. What relationships does pressure have to temperature?

How do you think impurities would affect the properties of a material?

 

[KoalaPowa]

From my notes, Pressure is proportional to Temperature (Pressure's Law). I know that the boiling point of water will increase if the pressure increases, because more energy is needed to overcome the intermolecular forces of attraction between water molecules as well as to overcome the increased pressure.
For pressure affecting the melting/freezing point, my notes just say that increased pressure will cause the melting/freezing point to become lower, but they don't explain why.
For impurities, the notes only mention about the boiling point increasing and the melting/freezing point decreasing, also not explaining why.
Is there any way i can apply Pressure's Law (Pressure proportional to Temp.), Charle's Law (Volume proportional to Temp.) and Boyle's Law (Pressure inversely proportional to Volume)?

My take on pressure affecting the melting/freezing point of water is that when pressure is applied to ice, the temperature of the ice will increase (Pressure's Law). When temp. increases, it melts and the volume also decreases (Boyle's Law). So does that mean that for water to become ice again, it will have to lose more energy, thus a lower melting/freezing point? That's where I am left clueless. My understanding of the concept isn't really there yet.

As for impurities, I have really no idea how to start as my notes are just too brief and do not explain anything.

 

[NascentOxygen]

As for impurities, I have really no idea how to start as my notes are just too brief and do not explain anything.

In situations where your notes are too brief, or confusing, there are plenty of online resources you can consult. A good one is http://ask.com where you type in your question, and it comes up with lots of links. Ignore those which are clearly off topic, and refer to some which address your question. Read at least 4 or 5 of the sources, because, after all, this is the web and not all authors are as well-intentioned or as well-informed as we'd hope.

A suitable question to put to ask.com is: how do impurities affect the freezing point of water?

 

[rwisz]

1. Pressure is increased:

When pressure is increased, the molecules in a substance are forced closer together. In the case of water, this means that the molecules are pushed closer together, making it harder for them to break away from each other and change state from solid to liquid, or liquid to gas. This results in an increase in the melting and boiling points of water.

In order to melt, the molecules in a solid must have enough energy to break away from their fixed positions and move around as a liquid. Similarly, in order to boil, the molecules in a liquid must have enough energy to break free from the surface and escape as a gas. When pressure is increased, the molecules are more tightly packed and it takes more energy for them to break free, resulting in a higher melting and boiling point.

2. Impurities are added:

Impurities are substances that are not chemically bonded to the water molecules, but are mixed in with them. These impurities can affect the melting and boiling point of water in different ways, depending on the type and amount of impurities present.

One possible effect is that impurities can disrupt the orderly arrangement of water molecules in a solid, making it easier for them to break away from each other and melt at a lower temperature. This is because the impurities take up space between the water molecules, preventing them from being as tightly packed as they would be in pure water.

On the other hand, impurities can also increase the boiling point of water. This is because the impurities can form stronger bonds with the water molecules, making it harder for them to escape and turn into a gas. This results in a higher boiling point for the water.

In summary, pressure and impurities can both affect the melting and boiling points of water by altering the arrangement and strength of the bonds between water molecules.