Change of State: Breaking Down What Really Happens

[MathewsMD]

What exactly happens in a change of state? For example, when water turns to ice at 0 degrees Celsius, there is no temperature change, volume change or pressure change. So what exactly is changing? Are intermolecular bonds being broken/formed? If so, why does this not affect the volume of the substance?

 

[Nugatory]

why does this not affect the volume of the substance?

It does. Ice at 0 Celsius floats in water at 0 Celsius, for example.

 

[K^2]

There are plenty of examples where volume does not change, though. Water is a really special case.

Phase transition is all about entropy. In simple terms, something about the way matter is organized has to change. This can be atoms arranging themselves in a lattice when molten metal solidifies, for example. Or it can be just molecules orienting themselves in the same direction, such as the case with liquid crystals. Or a really interesting case of a feromagnetic, such as a piece of iron, taken past Curie point. Nothing in the structure changes. Atoms remain organized in the same lattice as before. But individual spins go from being all in the same direction (within a domain) to being randomly oriented. Iron stops being a feromagnetic, but in every other way, it's the same piece of iron.

So phase change can be fairly interesting. It doesn't have to be a change of state of matter. It can be an internal change that's difficult to detect right away. But something does always change.

 

[SteamKing]

The remarkable aspect of the volume change in water as liquid turns to solid is that the volume increases. In many other substances, the volume of the solid is smaller than the volume of the liquid.

 

[pmacias]

In a change of state, the physical state of a substance is altered from one form to another, such as from a solid to a liquid or from a liquid to a gas. This change is a result of the rearrangement of the molecules within the substance. When water turns to ice at 0 degrees Celsius, there is no change in temperature, volume, or pressure because the water molecules are simply rearranging themselves into a more ordered, crystalline structure.

During this process, intermolecular bonds between the water molecules are indeed being formed and broken. In liquid water, the molecules are constantly moving and interacting with each other, but in ice, the molecules are held in a rigid, lattice structure by strong hydrogen bonds. This rearrangement of molecules does not affect the overall volume of the substance because the molecules are still tightly packed together, just in a different arrangement.

It is important to note that a change of state is a physical change, meaning the chemical composition of the substance remains the same. Only the arrangement of the molecules is altered. This is why there is no change in temperature, volume, or pressure during a change of state.

In summary, a change of state involves the rearrangement of molecules within a substance, resulting in a different physical state. While intermolecular bonds are being formed and broken, the overall volume of the substance remains the same due to the close packing of the molecules.