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Vapor pressure, partial pressure, and dalton’s law

Vapor pressure is defined as the pressure at which a gas coexists with its solid or liquid phase. Vapor pressure is created by faster molecules that break away from the liquid or solid and enter the gas phase. The vapor pressure of a substance depends on both the substance and its temperature—an increase in temperature increases the vapor pressure.

Partial pressure is defined as the pressure a gas would create if it occupied the total volume available. In a mixture of gases, the total pressure is the sum of partial pressures of the component gases , assuming ideal gas behavior and no chemical reactions between the components. This law is known as Dalton’s law of partial pressures    , after the English scientist John Dalton (1766–1844), who proposed it. Dalton’s law is based on kinetic theory, where each gas creates its pressure by molecular collisions, independent of other gases present. It is consistent with the fact that pressures add according to Pascal’s Principle . Thus water evaporates and ice sublimates when their vapor pressures exceed the partial pressure of water vapor in the surrounding mixture of gases. If their vapor pressures are less than the partial pressure of water vapor in the surrounding gas, liquid droplets or ice crystals (frost) form.

Is energy transfer involved in a phase change? If so, will energy have to be supplied to change phase from solid to liquid and liquid to gas? What about gas to liquid and liquid to solid? Why do they spray the orange trees with water in Florida when the temperatures are near or just below freezing?

Yes, energy transfer is involved in a phase change. We know that atoms and molecules in solids and liquids are bound to each other because we know that force is required to separate them. So in a phase change from solid to liquid and liquid to gas, a force must be exerted, perhaps by collision, to separate atoms and molecules. Force exerted through a distance is work, and energy is needed to do work to go from solid to liquid and liquid to gas. This is intuitively consistent with the need for energy to melt ice or boil water. The converse is also true. Going from gas to liquid or liquid to solid involves atoms and molecules pushing together, doing work and releasing energy.

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Phet explorations: states of matter—basics

Heat, cool, and compress atoms and molecules and watch as they change between solid, liquid, and gas phases.

States of Matter: Basics

Section summary

  • Most substances have three distinct phases: gas, liquid, and solid.
  • Phase changes among the various phases of matter depend on temperature and pressure.
  • The existence of the three phases with respect to pressure and temperature can be described in a phase diagram.
  • Two phases coexist (i.e., they are in thermal equilibrium) at a set of pressures and temperatures. These are described as a line on a phase diagram.
  • The three phases coexist at a single pressure and temperature. This is known as the triple point and is described by a single point on a phase diagram.
  • A gas at a temperature below its boiling point is called a vapor.
  • Vapor pressure is the pressure at which a gas coexists with its solid or liquid phase.
  • Partial pressure is the pressure a gas would create if it existed alone.
  • Dalton’s law states that the total pressure is the sum of the partial pressures of all of the gases present.

Conceptual questions

A pressure cooker contains water and steam in equilibrium at a pressure greater than atmospheric pressure. How does this greater pressure increase cooking speed?

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Why does condensation form most rapidly on the coldest object in a room—for example, on a glass of ice water?

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What is the vapor pressure of solid carbon dioxide (dry ice) at 78 . 5 º C size 12{ +- "78" "." 5°C} {} ?

The phase diagram (pressure versus temperature graph showing the three phases) for carbon dioxide. The triple point is five point one one atmospheres and negative fifty-six point six degrees Celsius. The critical point is seventy-three atmospheres and thirty-one degrees C. The phase change from solid to vapor at standard pressure of one atmosphere is negative seventy-eight point five degrees C.
The phase diagram for carbon dioxide. The axes are nonlinear, and the graph is not to scale. Dry ice is solid carbon dioxide and has a sublimation temperature of 78 . 5 º C size 12{ +- "78" "." 5°C} {} .
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Can carbon dioxide be liquefied at room temperature ( 20 º C size 12{"20"°C} {} )? If so, how? If not, why not? (See [link] .)

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Oxygen cannot be liquefied at room temperature by placing it under a large enough pressure to force its molecules together. Explain why this is.

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What is the distinction between gas and vapor?

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Questions & Answers

Suppose a speck of dust in an electrostatic precipitator has 1.0000×1012 protons in it and has a net charge of –5.00 nC (a very large charge for a small speck). How many electrons does it have?
Alexia Reply
how would I work this problem
how can you have not an integer number of protons? If, on the other hand it supposed to be 1e12, then 1.6e-19C/proton • 1e12 protons=1.6e-7 C is the charge of the protons in the speck, so the difference between this and 5e-9C is made up by electrons
what is angular velocity
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Mya Reply
Why is light bright?
Abraham Reply
what is radioactive element
Attah Reply
an 8.0 capacitor is connected by to the terminals of 60Hz whoes rms voltage is 150v. a.find the capacity reactance and rms to the circuit
Aisha Reply
thanks so much. i undersooth well
Valdes Reply
what is physics
Nwafor Reply
is the study of matter in relation to energy
a submersible pump is dropped a borehole and hits the level of water at the bottom of the borehole 5 seconds later.determine the level of water in the borehole
Obrian Reply
what is power?
aron Reply
power P = Work done per second W/ t. It means the more power, the stronger machine
e.g. heart Uses 2 W per beat.
A spherica, concave shaving mirror has a radius of curvature of 32 cm .what is the magnification of a persons face. when it is 12cm to the left of the vertex of the mirror
Alona Reply
did you solve?
my name is Abu m.konnek I am a student of a electrical engineer and I want you to help me
the magnification k = f/(f-d) with focus f = R/2 =16 cm; d =12 cm k = 16/4 =4
what do we call velocity
A weather vane is some sort of directional arrow parallel to the ground that may rotate freely in a horizontal plane. A typical weather vane has a large cross-sectional area perpendicular to the direction the arrow is pointing, like a “One Way” street sign. The purpose of the weather vane is to indicate the direction of the wind. As wind blows pa
Kavita Reply
what about the wind vane
If a prism is fully imersed in water then the ray of light will normally dispersed or their is any difference?
Anurag Reply
the same behavior thru the prism out or in water bud abbot
If this will experimented with a hollow(vaccum) prism in water then what will be result ?
What was the previous far point of a patient who had laser correction that reduced the power of her eye by 7.00 D, producing a normal distant vision power of 50.0 D for her?
Jaydie Reply
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
What is the far point of a person whose eyes have a relaxed power of 50.5 D?
A young woman with normal distant vision has a 10.0% ability to accommodate (that is, increase) the power of her eyes. What is the closest object she can see clearly?
29/20 ? maybes
In what ways does physics affect the society both positively or negatively
Princewill Reply

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