phase change
Evaporation
-Change of phase from liquid to gas
Sublimation
-Form of phase change directly from solid to gas•Example: dry ice (solid carbon dioxide molecules), mothballs, frozen water
Freezing
-Occurs when a liquid changes to a solid-Opposite of melting-When energy is continually removed from a liquid, molecular motion decreases until the forces of attraction bind them together and formation of ice occurs.
Melting
-Occurs when a substance changes phase from a solid to a liquid-Opposite of freezing-When heat is supplied to a solid, added vibration breaks molecules loose from the structure and melting occurs.
Heat of vaporization for water is
2256 joules/g.
Heat of fusion for water is
334 joules/g.
Matter exists in four common phases that involve transfer of internal energy
:-Solid phase (ice) -Liquid phase (ice melts to water )-Gaseous phase (water turns to vapor; addition of more energy vaporizes water to vapor )-Plasma phase (vapor disintegrates to ions and electrons)
The process of boiling
A.cools the water being boiled.B.depends on atmospheric pressure. C.is a change of phase below the water surface.
When you step out after a hot shower you feel cold, but you can feel warm again if you step back into the shower area. Which process is responsible for this?
Condensation
evaporation and our bodies:
Important in cooling our bodies when we overheat-Sweat glands produce perspiration.-Water on our skin absorbs body heat as evaporation cools the body.-Helps to maintain a stable body temperature.
condensation
Opposite of evaporation-Warming process from a gas to a liquid-Gas molecules near a liquid surface are attracted to the liquid-They strike the surface with increased kinetic energy, becoming part of the liquid
latent heat of vaporization
The amount of energy required to change a unit mass of a substance from liquid to gas ad vice versa
latent heat of fusion
The amount of energy required to change a unit mass of a substance from solid to liquid and vice versa
relative humidity
The amount of water vapor in the air at any given time is usually less than that required to saturate the air. Expressed as a percentage.
regelation
The process of melting under pressure and the subsequent refreezing when the pressure is removed.
Condensation in the atmosphere-
When the temperature of the atmosphere is low, the water molecules in the air move slowly.-Slow-moving water molecules stick together, causing condensation.
heat pump
a device that uses work to transfer thermal energy from a colder area to a warmer area
humidity
a measure of the amount of water vapor in the air mass of water per volume of air
Cooling cycle of refrigerator pumps
a special fluid that vaporizes and draws heat from stored food. The gas that forms, along with its energy, is directed to the condensation coils outside the fridge where heat is released and the fluid condenses back to liquid.
to chnage phase From solid to liquid to gas phase•
add energy
saturated air
air that contains as much water vapor as is possible for that temperature
difference between fog and cloud
altitude. fog is cloud at ground level
Some energetic molecules escape from the liquid and
become gas. Average kinetic energy of the remaining molecules in the liquid decreases, resulting in cooler water.
at high altitudes, water
boils at alower temp Example:Buildup of vapor pressure inside a pressure cooker prevents boiling, thus resulting in a higher temperature that cooks the food.Water boils at 95ºC in Denver, CO (high altitude) instead of at 100ºC (sea level).
cool air has a higher chance for
condensation and saturation, as molecules move slower so moreliekly stick together
Change from Solid Liquid Gas Plasma requires
energy to be added to the material.
why does evaporation cool
excited hot molecules leave, and the substance left is cooled
a pure substance has a definite
freezing or melting point at any given pressure
Air conditioner pumps heat energy
from one part of the unit to another
the amount of energy needed to melt ice and boil
is same as the amount of energy release when freezing or condensing
why does pressure cooker reach hgier temp than boiling
it prevents boiling, a cooling process,so it only heats
wehn water turns into gas
its called water vapor
add some energy- ice goes to
liquid, gas, then plasma
Energy causes the molecules to
move more rapidly.
boiling
phase change throughout liquid rather than only surface Rapid evaporation from beneath the surface of a liquid. Rapid form of evaporation beneath the surface forms vapor bubbles.-Bubbles rise to the surface.-If vapor pressure in the bubble is less than the surrounding pressure, then the bubbles collapse.-Hence, bubbles don't form at temperatures below boiling point (vapor pressure is insufficient).
•Farmers in cold climates replace frozen tubs of water with unfrozen ones in their cellars to
prevent jars of food from freezing.
we can boil a substance by
putting it into a vaccum , which then freezes it as boiling is a cooling process
to change phase From gas to liquid to solid phase•
remove energy
Kinetic energy is absorbed by the liquid in condesation
resulting in increased temperature.
A cold soda pop can is wet in warm air because
slow-moving molecules make contact with the cold surface and condense.
In dry cities, the rate of evaporation from your skin is greater than the rate of condensation,
so you feel colder.
boiling point depends on botj
temp and pressure
The phase of material depends upon
the temperature and pressure.
Boiling water at 100ºC is in
thermal equilibrium—boiling water is being cooled as fast as it is being warmed.-In this sense, boiling is a cooling process.
changes of phase almost awalways require
transfer of energy
•In briefly touching a hot skillet with wet finger, energy that normally would flow into your finger instead
vaporizes water. Hence, you're not burned.
steam
water in vapor form; invisible gas made when water is heated to the boiling point 100c
does frozen water evaporate?
yes, called sublimatnion
