Download Phase Diagrams

Phase Diagrams
Chapters 13 section 4
Phase Diagrams

Show the relationship between temperature,
pressure and state of matter
– Points on the line: exist as both phases
– Triple point: all three phases at once
– Critical point: can’t exist as a liquid above this
point
At critical temperature: increasing pressure won’t
change a gas to a liquid
 At critical pressure: the pressure required to liquefy a
gas at its critical temperature

Normal Boiling/Freezing Points: occur at
1 atm of pressure
Dynamic Equilibrium
• Dynamic equilibrium: movement of an equal
# of
particles back and forth from one state of matter to another.
•rate of one phase change must equal the rate of another
phase change.
(a)– Open Container
NOT at equilibrium
(b) Closed Container - at
equilibrium between
liquid and vapor phases
- rate of evaporation
equals the rate of
condensation.
How Temperature Affects the Vapor Pressure
• Vapor Pressure is simply the push of a gas above its liquid.
• As the temperature of a liquid increases, so does the number of vapor
particles.
• More vapor particles cause more collisions,
therefore more vapor
pressure. [Direct Relationship: (T ↑ Vapor Pressure ↑)]
Low Temperature
High Temperature
Why Liquids Boil
• Any liquid will boil when the atmospheric (air) pressure
equals the vapor pressure of the liquid.
•Inside of the bubble there is water vapor pressure
pushing outward which keeps the shape of the bubble.
vapor
liquid
This image shows the innerright-side of a bubble.
Why Liquids Boil (Continued)
• Before the water gets hot
enough, the bubble gets squished
by the external atmospheric
pressure pushing in as the bubble
moves up through the water
•The bubble won’t quite make
it to the surface—no boiling
• When the internal water vapor
pressure equals the external air
pressure, the bubble keeps its
shape to the top
•water boils.
Key:
= interior water vapor pressure
= exterior atmospheric pressure
3 Ways to Make Water Boil: How to Get the Pressures Equal
(1) Heat it up: Raising the temperature of the water will increase the
vapor pressure until it equals the atmospheric pressure.
(2) Use a vacuum pump: Lower the external pressure above the liquid
by pulling out the air until the atmospheric pressure is equal to the
vapor pressure of the water.
(3) Do both: Lower the air pressure and heat it.
“Normal Boiling Point” of Water
• At standard pressure (760 mm Hg), water’s normal B.P = 100˚C.
• Once a liquid is boiling, adding heat DOES NOT increase its
temperature. The liquid simply bubbles more.
• On a mountain, the atm. pressure is lower, therefore the temperature
at which the water boils is less than 100˚C.
• Foods in boiling water on a mountain
will take longer to cook since the boiling
water is cooler .
•Some foods, like breads and cakes,
have special cooking instructions for
high altitudes.
Boiling Water Above 100 ºC
• In a pressure cooker, the atm. pressure is higher, therefore the
temperature at which the water boils is more than 100˚C. Foods in a
pressure cooker will cook faster since the water is hotter.
• Water that’s next to volcanic vents on the ocean’s floor will reach
temperatures well above 100˚ C, but it won’t “boil” since the
surrounding pressure is so great!
Boiling Points vs. Pressure
Practice Problems:
1) What is the normal boiling point for ethanoic acid? _______
2) At what temperature will ethanoic acid boil on Mt. Everest when
the pressure is only 30 kPa? _______