Transcript 61st Vapor pressure _ phase diagram

Aim:
I.O.SWBAT:
1) Define vapor pressure
2) Interpret phase change diagrams
3) Describe critical temperature and pressure
4) Draw a phase change diagram
MOTIVATION: What happens ice at -25oC if your add heat to it?
Do-Now: How does the behavior of a liquid in a closed
container differ from that in an open one?
Vapor: Gas form of
a substance that is
a solid or a liquid at
room temperature.
LIQUID
GAS
Dynamic equilibrium: Vaporization and condensation
occur at the same rate.
Vapor pressure: partial
pressure of the vapor
over the liquid measured
at equilibrium
As more molecules escape the liquid, the pressure
they exert increases.
• At any temperature, some molecules in a liquid
have enough energy to escape.
• As the temperature rises, the fraction of molecules
that have enough energy to escape increases.
Boiling point: is the temperature at which the vapor
pressure of a liquid equals the surroundings pressure.
Vapor Pressure Curves
The normal boiling point is the temperature at which its
vapor pressure is 760 torr.
Volatility: The tendency of a
substance to evaporate easily.
Volatile liquids: Liquids with a
high vapor pressure and weak
intermolecular forces.
(have low boiling points )
PRACTICE:
1)Why does the vapor pressure of a liquid depend on
intermolecular forces?
2)Why does it take longer to hard boil an egg at high
elevations?
3)How does a pressure cooker cook food faster?
Do-Now: Complete hand-out.
Phase diagram: Is a graphic representation of the
relationships between the physical state of a
substance and its pressure and temperature.
• The AB line is the liquid-vapor interface.
• Each point along this line is the boiling point
of the substance at that pressure.
• Triple point (A): solid, liquid and gas are in
nequilibrium.
• Critical point (B): Beyond this temperature gas
cannot be liquefied by increasing pressure.
• The AD line is the interface between liquid and
solid.
• The melting point at each pressure can be found
along this line.
• Below A the substance cannot exist in the
liquid state.
• Along the AC line the solid and gas phases
are in equilibrium.
(the sublimation point at each pressure is along
this line)
Phase Diagram of Water
• The slope of the solid–
liquid line is negative.
– As the pressure is increased
at a temperature just below
the melting point, water goes
from a solid to a liquid.
• The high critical point of
water is due to the
strong van der Waals
forces between water
molecules.
Phase Diagram of Carbon Dioxide
• Carbon dioxide cannot exist
in the liquid state at
pressures below 5.11 atm.
• CO2 sublimes at normal
pressures.
Isotherm: constant temperature
Isobar: constant pressure
PRACTICE:
Complete Hand-Out
HW#44