<< Chapter < Page Chapter >> Page >


We have observed and defined phase transitions and phase equilibrium. We have also observed equilibrium in avariety of reaction systems. We will assume an understanding of the postulates of the Kinetic Molecular Theory and of the energetics of chemical reactions.


We have developed an understanding of the concept of equilibrium, both for phase equilibrium and reactionequilibrium. As an illustration, at normal atmospheric pressure, we expect to find H 2 O in solid form below 0°C, in liquid form below 100°C, and in gaseous form above 100°C. What changes as we movefrom low temperature to high temperature cause these transitions in which phase is observed? Viewed differently, if a sample of gaseouswater at 120°C is cooled to below 100°C, virtually all of the water vapor spontaneously condenses to form theliquid: H 2 O ( g ) H 2 O ( l ) spontaneous below100°C By contrast, very little of liquid water at 80°C spontaneously converts to gaseous water: H 2 O ( l ) H 2 O ( g ) not spontaneous below100°C We can thus rephrase our question as, what determines which processes are spontaneous and which are not? Whatfactors determine what phase is "stable"?

As we know, at certain temperatures and pressures, more than one phase can be stable. For example, at 1 atmpressure and 0°C, H 2 O ( s ) H 2 O ( l ) equilibrium at 0°C Small variations in the amount of heat applied or extracted to the liquid-solid equilibrium cause shifts towardsliquid or solid without changing the temperature of the two phases at equilibrium. Therefore, when the two phases are at equilibrium,neither direction of the phase transition is spontaneous at 0°C. We therefore need to understand what factors determinewhen two or more phases can co-exist at equilibrium.

This analysis leaves unanswered a series of questions regarding the differences between liquids and gases. Theconcept of a gas phase or a liquid phase is not a characteristic of an individual molecule. In fact, it does not make any sense torefer to the "phase" of an individual molecule. The phase is a collective property of large numbers of molecules.Although we can discuss the importance of molecular properties regarding liquid and gas phases, we have not discussed the factorswhich determine whether the gas phase or the liquid phase is most stable at a given temperature and pressure.

These same questions can be applied to reaction equilibrium. When a mixture of reactants and products isnot at equilibrium, the reaction will occur spontaneously in one direction or the other until the reaction achieves equilibrium.What determines the direction of spontaneity? What is the driving force towards equilibrium? How does the system know that equilibrium has been achieved? Our goal will be to understand the driving forces behind spontaneousprocesses and the determination of the equilibrium point, both for phase equilibrium and reaction equilibrium.

Observation 1: spontaneous mixing

We begin by examining common characteristics of spontaneous processes, and for simplicity, we focus on processesnot involving phase transitions or chemical reactions. A very clear example of such a process is mixing. Imagine putting a drop of blueink in a glass of water. At first, the blue dye in the ink is highly concentrated. Therefore, the molecules of the dye areclosely congregated. Slowly but steadily, the dye begins to diffuse throughout the entire glass of water, so that eventually the waterappears as a uniform blue color. This occurs more readily with agitation or stirring but occurs spontaneously even without sucheffort. Careful measurements show that this process occurs without a change in temperature, so there is no energy input or releasedduring the mixing.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, General chemistry ii. OpenStax CNX. Mar 25, 2005 Download for free at http://cnx.org/content/col10262/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'General chemistry ii' conversation and receive update notifications?