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A beaker of water being heated over a flame. The beaker is shown at three different times. In the first, at twenty degrees C, a small bubble sits on the bottom of the beaker. In the second step, the water temperature is fifty degrees C and the bubble is larger, though still sitting on the bottom of the beaker. In the third step, the water temperature is one hundred degrees C. The bubble is larger and is rising toward the surface.
(a) An air bubble in water starts out saturated with water vapor at 20 º C size 12{"20"°C} {} . (b) As the temperature rises, water vapor enters the bubble because its vapor pressure increases. The bubble expands to keep its pressure at 1.00 atm. (c) At 100 º C size 12{"100"°C} {} , water vapor enters the bubble continuously because water’s vapor pressure exceeds its partial pressure in the bubble, which must be less than 1.00 atm. The bubble grows and rises to the surface.

Freeze drying is a process in which substances, such as foods, are dried by placing them in a vacuum chamber and lowering the atmospheric pressure around them. How does the lowered atmospheric pressure speed the drying process, and why does it cause the temperature of the food to drop?

Decreased the atmospheric pressure results in decreased partial pressure of water, hence a lower humidity. So evaporation of water from food, for example, will be enhanced. The molecules of water most likely to break away from the food will be those with the greatest velocities. Those remaining thus have a lower average velocity and a lower temperature. This can (and does) result in the freezing and drying of the food; hence the process is aptly named freeze drying.

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Phet explorations: states of matter

Watch different types of molecules form a solid, liquid, or gas. Add or remove heat and watch the phase change. Change the temperature or volume of a container and see a pressure-temperature diagram respond in real time. Relate the interaction potential to the forces between molecules.

States of Matter: Basics

Section summary

  • Relative humidity is the fraction of water vapor in a gas compared to the saturation value.
  • The saturation vapor density can be determined from the vapor pressure for a given temperature.
  • Percent relative humidity is defined to be
    percent relative humidity = vapor density saturation vapor density × 100 . size 12{ size 11{"percent relative humidity"= { { size 11{"vapor density"}} over { size 11{"saturation vapor density"}} } times "100" "." }} {}
  • The dew point is the temperature at which air reaches 100% relative humidity.

Conceptual questions

Because humidity depends only on water’s vapor pressure and temperature, are the saturation vapor densities listed in [link] valid in an atmosphere of helium at a pressure of 1 . 01 × 10 5 N/m 2 size 12{1 "." "01"´"10" rSup { size 8{5} } " N/m" rSup { size 8{2} } } {} , rather than air? Are those values affected by altitude on Earth?

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Why does a beaker of 40 . 0 º C size 12{"40" "." 0°C} {} water placed in a vacuum chamber start to boil as the chamber is evacuated (air is pumped out of the chamber)? At what pressure does the boiling begin? Would food cook any faster in such a beaker?

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Why does rubbing alcohol evaporate much more rapidly than water at STP (standard temperature and pressure)?

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Dry air is 78.1% nitrogen. What is the partial pressure of nitrogen when the atmospheric pressure is 1 . 01 × 10 5 N/m 2 size 12{1 "." "01"´"10" rSup { size 8{5} } " N/m" rSup { size 8{2} } } {} ?

7 . 89 × 10 4 Pa size 12{ size 11{7 "." "89" times "10" rSup { size 8{4} } " Pa"}} {}

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(a) What is the vapor pressure of water at 20 . 0 º C size 12{"20" "." 0°C} {} ? (b) What percentage of atmospheric pressure does this correspond to? (c) What percent of 20 . 0 º C size 12{"20" "." 0°C} {} air is water vapor if it has 100% relative humidity? (The density of dry air at 20 . 0 º C size 12{"20" "." 0°C} {} is 1 . 20 kg/m 3 size 12{1 "." "20"" kg/m" rSup { size 8{3} } } {} .)

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Pressure cookers increase cooking speed by raising the boiling temperature of water above its value at atmospheric pressure. (a) What pressure is necessary to raise the boiling point to 120 . 0 º C size 12{"120" "." 0°C} {} ? (b) What gauge pressure does this correspond to?

(a) 1 . 99 × 10 5 Pa size 12{ size 11{1 "." "99" times "10" rSup { size 8{5} } " Pa"}} {}

(b) 0.97 atm

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Questions & Answers

the definition of photon
Bright Reply
8kg of a hot liquid initial T is 90°© is missed with another liquid 3kg at 20° calculate e équilibrium T
Balki Reply
8kg of a hot liquid initial T is 90°© is missed with another liquid 3kg at 20° calculate e équilibrium T
answer plz
what are the products when acid and base mixed?
salt and water
What's this place about?
@Austin your answer should be SALT and WATER
salts and water
what work done
Dennis Reply
work done is the product of force and distance moved in the direction of force
Work done = force (F) * distance (D)
what is resounance
explain the three laws of isaac Newton with the reference
glory Reply
1st law ; a body will continue to stay at a state of rest or continue to move at a uniform motion on a straight line unless an external force is been acted upon
3rd law; in every action there is an equal or opposite reaction
2nd law: F=ma
why am i not having access to the Link in your exemples /figures ?
Augustine Reply
what is circut
hasiya Reply
newtons law of motion
First law:In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.
is the ability to do work
Adjah Reply
u from
any body online hain
ability to do work is energy
what is energy
Mercy Reply
energy is ability of the capacity to doing work
what is vector
mosco Reply
A quantity that has both magnitude and direction
can a body with out mass float in space
Is the quantity that has both magnitude and direction
Yes it can float in space,e.g.polyethene has no mass that's why it can float in space
that's my suggestion,any other explanation can be given also,thanks
A charge of 1.6*10^-6C is placed in a uniform electric field in a density 2*5^10Nc^-1, what is the magnitude of the electric force exerted on the charge?
Omotosho Reply
what's phenomena
Enoch Reply
Phenomena is an observable fact or event.
Prove that 1/d+1/v=1/f
James Reply
What interference
Moyinoluwa Reply
What is a polarized light called?
what is a half life
Mama Reply
the time taken for a radioactive element to decay by half of its original mass
what is radioactive element
Half of the total time required by a radioactive nuclear atom to totally disintegrate
radioactive elements are those with unstable nuclei(ie have protons more than neutrons, or neutrons more than protons
in other words, the radioactive atom or elements have unequal number of protons to neutrons.
state the laws of refraction
state laws of reflection
Why does a bicycle rider bends towards the corner when is turning?
When do we say that the stone thrown vertically up wards accelerate negatively?
Give two importance of insulator placed between plates of a capacitor.
Macho had a shoe with a big sole moving in mudy Road, shanitah had a shoe with a small sole. Give reasons for those two cases.
when was the name taken from
Biola Reply
retardation of a car
when was the name retardation taken
did you mean a motion with velocity decreases uniformly by the time? then, the vector acceleration is opposite direction with vector velocity
what's velocity
Velocity is the rate of change of displacement
Practice Key Terms 4

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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