Unit 8 Flashcards
(22 cards)
When a liquid boils in the presence of air the pressure exerted on the liquid by its escaping molecules is called what?
Partial pressure
From a phase diagram where can you see all phases at equilibrium?
At the triple point
Where all lines intersect
What happens above critical point?
There is one indistinguishable phase
What does the triple point represent?
Where solid liquid and vapour are in equilibrium
What is the phase process called in which a solid transforms into a gas?
Sublimation
In the phase diagram of water the line between solid and vapour is positive, Why?
Because the energy change will be positive. Ice has a much smaller volume than its gas so there will be a positive value for volume in the clapeyron equation, meaning positive slope
The most stable phase at a given temperature will be the one with what?
The lowest Gibbs energy
What is supercooling of a pure metal?
The metal cools below freezing point to form a metastable phase. Crystallisation can be prompted, when the crystals form heat is given out which heats it back up to freezing point and freezing can continue
What is it called when the escaping vapour exerts a pressure on the liquid?
Vapour pressure
What does volatile mean>
Has high vapour pressure
What is vapour pressure?
The escaped vapour exerts a pressure on the remaining liquid
What is vapour pressure called in a closed system, and whats different about it?
Saturated vapour pressure
In a closed system an equilibrium between vapour and liquid happens
When does a liquid boil?
When vapour pressure of a liquid is equal to atmospheric pressure
Water phase diagram is unusual, has a negative slope between ice and water, why?
Ice occupies a larger volume than water due to hydrogen bonding this makes the change in V negative in the claperyon equation, giving a negative slope
What is the pressure exerted on liquid molecules by leaving molecules called when there is another gas present?
Partial pressure
How many stable allotropes of sulphur?
2
What is supercritical fluid?
The material produced above critical point, it has properties of both a liquid and a vapour
When is a chemical system at equilibrium?
When gibbs is at its minimum
Why do we use chromatography?
separate a mixture to determine identity
what does the rate of how fast a compound move up the chromatography paper depend on?
How the compound interacts with the solvent and solid (stationary) phase
What is retention time?
how far a compound moves on chromatography paper
On a chromatogram what phase will the last substance interact with the most?
Stationary phase
