<< Chapter < Page Chapter >> Page >

It is important to note that we can vary the relative amount ofNH 3 produced by varying the temperature of the reaction, the volume of the vessel in which the reaction occurs, or the relative startingamounts of N 2 and H 2 . We shall study and analyze this observation in detail in latersections. For now, though, we demonstrate that the concept of reaction equilibrium is general to all reactions.

Consider the reaction

H 2 ( g ) + I 2 ( g ) 2 H I ( g )

If we begin with 1.00 mole of H 2 and 1.00 mole of i 2 at 500 K in a reaction vessel of fixed volume, we observe that, at equilibrium, n H I 1.72 mol , leaving in the equilibrium mixture n H 2 0.14 mol and n I 2 0.14 mol .

Similarly, consider the decomposition reaction

N 2 O 4 ( g ) 2 N O 2 ( g )

At 298K in a 100.0L reaction flask, 1.00 mol ofN 2 O 4 partially decomposes to produce, at equilibrium, n N O 2 0.64 mol and n N 2 O 4 0.68 mol .

Some chemical reactions achieve an equilibrium that appears to be very nearly complete reaction. Forexample,

H 2 ( g ) + Cl 2 ( g ) 2 H Cl ( g )

If we begin with 1.00 mole of H 2 and 1.00 mole of Cl 2 at 298K in a reaction vessel of fixed volume, we observe that, at equilibrium, n H Cl is almost exactly 2.00 mol, leaving virtually no H 2 or Cl 2 This does not mean that the reaction has not come to equilibrium. It means instead that, at equilibrium, there are essentially noreactants remaining.

In each of these cases, the amounts of reactants and products present at equilibrium vary as theconditions are varied but are completely reproducible for fixed conditions. Before making further observations that will lead to aquantitative description of the reaction equilibrium, we consider a qualitative description of equilibrium.

We begin with a dynamic equilibrium description. We know from our studies of phase transitions thatequilibrium occurs when the rate of the forward process ( e.g. evaporation) is matched by the rate of reverse process ( e.g. condensation). Since we have now observed that gas reactions also come to equilibrium, we postulate that at equilibrium the forwardreaction rate is equal to the reverse reaction rate. For example, in the reaction here , the rate of decomposition ofN 2 O 4 molecules at equilibrium must be exactly matched by the rate ofrecombination (or dimerization ) of NO 2 molecules.

To show that the forward and reverse reactions continue to happen at equilibrium, we start with theNO 2 and N 2 O 4 mixture at equilibrium and we vary the volume of the flask containing the mixture. We observe that, if we increase the volumeand the reaction is allowed to come to equilibrium, the amount of NO 2 at equilibrium is larger at the expense of a smaller amount of N 2 O 4 . We can certainly conclude that the amounts of the gases atequilibrium depend on the reaction conditions. However, if the forward and reverse reactions stop once the equilibrium amounts ofmaterial are achieved, the molecules would not "know" that the volume of the container had increased. Since the reactionequilibrium can and does respond to a change in volume, it must be that the change in volume affects the rates of both the forward andreverse processes. This means that both reactions must be occurring at equilibrium, and that their rates must exactly match atequilibrium.

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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 did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
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, Concept development studies in chemistry 2012. OpenStax CNX. Aug 16, 2012 Download for free at http://legacy.cnx.org/content/col11444/1.4
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 2012' conversation and receive update notifications?