Chapter 12 Charges Of Phase Flashcards
What is a closed system
One that matter cannot get into or out of.. But energy can
Define equilibrium
The dynamic condition in which two opposing changes occur at equal rates in the same closed system
Define a theoretical construct
No system can be completely closed but can come close
Define phase
Any part of a system with uniform composition and properties
Give an example of a phase
A flash of water with a stopper in it is a liquid vapor closed system. Here two phases are liquid and vapor
What can water molecules at the surface gain
Energy and escape the surface (evaporate)
What are h2o molecules below the surface held in place by
Surrounding molecules
Why do surface molecules evaporate easily
Because they are not held at the surface
What will some of the molecules do that escaped?
They will lose energy and return to the surface of the liquid (condense)
What happens if temperature remains constant
There will be a point where the amount evaporating will equal amounts condensing. Equilibrium will be established
What happens at equilibrium
The relative amounts of liquid and vapor will be constant not necessarily equal
Give two equilibrium expressions
Liquid + heat energy -> vapor (evap)
Vapor -> liquid + energy (condensation)
liquid+ heat vapor
What is Le Chatlier’s principle
When a system at equilibrium is disturbed by a stress, a new equilibrium point will be established that will minimize the stress
-for Le Chatlier’s, stress is a charge in pressure, temperature or volume of a container
What happens when you have more liquid at new equilibrium point
Add energy and reaction is pushed in reverse (right to left so more liquid at new equilibrium point; also less vapor)
What happens when pressure increases
Will push reaction equilibrium to the left
What happens when pressure decreases
Will push reaction equilibrium to the right
What happens when volume of the system increases
Pressure decreases
What happens when a volume of the system is decreased
Pressure increases
Define EVP
The pressure exerted by a vapor that is at equilibrium with its liquid temperature dependent
What happens if the temperature of the liquid is increased
More liquid molecules will gain enough KE to escape from the surface of the liquid
If the temperature of the liquid is increased what does it cause the vapor pressure to do
To increase, exerting a higher EVP, a new equilibrium point will be established with more vapor and use less liquid. Therefore EVP changes with temperature
Define volatile liquids
Give three examples
Evaporate quickly cause of weak attraction between molecules
Ether, ammonia, perfume
Define nonvolatile liquids
Give two examples
Evaporate slowly cause of strong attractions between molecules
Water, oil
Define boiling
The change of a liquid to a vapor within the liquid as well as a surface
When does boiling occur
When EVP equals atmospheric pressure at certain place and time
Define boiling point
It is temperature at which EVP of a specific liquid equals atmospheric pressure (which changes..)
What happens at low altitudes
Boiling point is low
What happens at high altitudes
Boiling point is high
What is constant at boiling point? Why?
Temperature is constant at boiling point, continued addition of heat provides energy to evaporate the liquid but temperature will not get higher
When will water boil faster but not hotter
Adding salt
To keep a liquid boiling what do you do
Continue to add heat
Define molar heat of evaporation
Amount of energy needed to vaporize one mole of a liquid at it’s boiling point
What kind of attraction do molecules have at high values & low values
Strong attraction ; weak attractions
When do freezing and melting occur
At same temperature for specific substances
What must a solid gain to become a liquid
Energy
What must a liquid lose to become a solid
Energy
