Criteria of purity and melting and boiling points Flashcards
(9 cards)
What is sublimation?
A phase change from a solid directly to a gas.
What is deposition?
A phase change from a gas directly to a solid.
What is the expected freezing point?
The temperature at which a liquid normally turns into a solid under standard conditions.
What is supercooling?
When a liquid is cooled below its freezing point but remains a liquid.
Why does supercooling happen?
The liquid is pure, with no nucleation sites (like dust or particles).
Gentle cooling means there’s not enough disturbance for molecules to bond and form a solid.
When disturbed, it freezes rapidly as molecules quickly bond into a solid structure.
Why do pure substances have fixed melting/boiling points?
All molecules have the same intermolecular forces, so they all change state at the same temperature when enough energy is provided.
Why do impure substances melt or boil over a range of temperatures?
Impurities disrupt the uniform structure, so different parts of the substance change state at different temperatures.
Why does state matter when discussing intermolecular forces?
In liquids and gases, particles are more randomly arranged, so their intermolecular forces are not uniform.
Why is the criteria of purity important in chemistry?
- Ensures substances like food, drinks, and medicine are free from harmful contaminants.
- Especially critical for medicines that go into the body, as impurities can be dangerous.
