<< Chapter < Page Chapter >> Page >

The vapor pressures of several liquids at several temperatures are shown in Figure 5. The vapor pressure for each liquid increases smoothly with temperature, although the relationship between vapor pressure and temperature is definitely not proportional.

The data in Figure 5 also clearly show that the vapor pressure depends strongly on what the liquid substance is. As an example, look at the vapor pressures of these five liquids at 50 ºC. The vapor pressure of phenol is tiny, whereas the vapor pressure of dimethyl ether is literally off the chart. The other three liquids have varying vapor pressures in between.

These variations in vapor pressure reflect the differing "volatilities" of the liquids: those with higher vapor pressures are more volatile, which makes sense since the liquid more readily transitions to the gaseous phase. In addition, there is a very interesting correlation between the volatility of a liquid and its boiling point. Without exception, the substances with high boiling points have low vapor pressures and vice versa. We will explore this correlation in detail in the next Concept Development Study.

Observation 3: Dynamic Equilibrium between Liquid and Gas Phases

There are several very interesting questions raised by our observations of phase equilibrium and vapor pressure. The first we will consider is why the vapor pressure at equilibrium with the liquid does not depend on the volume of the container into which the liquid evaporates. Nor does it depend on the amount of liquid in the container. Why do we always get the same pressure at equilibrium for the same temperature, regardless of other conditions? We need to understand how the vapor and liquid coexist in equilibrium. How is this equilibrium achieved?

To approach these questions, let us look again at the experimental set up in Figure 4. We begin with a container with a fixed volume containing some liquid, and equilibrium is achieved at the vapor pressure of the liquid at the fixed temperature given. When we adjust the volume to a larger fixed volume, the pressure automatically and immediately adjusts at equilibrium to exactly the same vapor pressure. This looks like magic. How is this possible?

Since the vapor exerts the same pressure in a larger volume at the same temperature, the Ideal Gas Law tells us that there are more molecules in the vapor after the volume is increased and equilibrium is reestablished. Therefore, more liquid must have evaporated to achieve this equilibrium, since the liquid is the only possible source of these extra molecules in the vapor phase. This leads us to ask how the liquid responded to the increase in overhead volume, since changing the volume presumably only affected the space in which the gas molecules move, not the liquid molecules. How did the liquid “know” to evaporate when the volume increased? We moved the piston, but the piston was not in contact with the liquid. So the molecules in the liquid could not detect the increase in volume for the gas, and thus could not possibly be responding to that increase. Nevertheless, more liquid molecules evaporated after the volume was increased.

Questions & Answers

what is mutation
Janga Reply
what is a cell
Sifune Reply
how is urine form
Sifune
what is antagonism?
mahase Reply
classification of plants, gymnosperm features.
Linsy Reply
what is the features of gymnosperm
Linsy
how many types of solid did we have
Samuel Reply
what is an ionic bond
Samuel
What is Atoms
Daprince Reply
what is fallopian tube
Merolyn
what is bladder
Merolyn
what's bulbourethral gland
Eduek Reply
urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
onuoha Reply
State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
Jeremiah
what is heart
Konadu Reply
how is urine formed in human
Konadu
how is urine formed in human
Rahma
what is the diference between a cavity and a canal
Pelagie Reply
what is the causative agent of malaria
Diamond
malaria is caused by an insect called mosquito.
Naomi
Malaria is cause by female anopheles mosquito
Isaac
Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
Olalekan
a canal is more needed in a root but a cavity is a bad effect
Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
Muhsin Reply
respiration is the process in which we breath in oxygen and breath out carbon dioxide
Achor
how are lungs work
Commander
where does digestion begins
Achiri Reply
in the mouth
EZEKIEL
what are the functions of follicle stimulating harmones?
Rashima Reply
stimulates the follicle to release the mature ovum into the oviduct
Davonte
what are the functions of Endocrine and pituitary gland
Chinaza
endocrine secrete hormone and regulate body process
Achor
while pituitary gland is an example of endocrine system and it's found in the Brain
Achor
what's biology?
Egbodo Reply
Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
Alfreda
Biology is the study of how living organisms live and survive in a specific environment
Sifune
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Concept development studies in chemistry 2013. OpenStax CNX. Oct 07, 2013 Download for free at http://legacy.cnx.org/content/col11579/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Concept development studies in chemistry 2013' conversation and receive update notifications?

Ask