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Observation 3: temperature dependence of the reaction equilibrium

We have previously observed that phase equilibrium, and in particular vapor pressure, depend on thetemperature, but we have not yet studied the variation of reaction equilibrium with temperature. We focus our initial study on this reaction and we measure the equilibrium partial pressures at a variety of temperatures. From these measurements, we can compile the datashowing the temperature dependence of the equilibrium constant K p for this reaction in [link] .

Equilibrium constant for the synthesis of hi
T (K) K p
500 6.25 × 10 –3
550 8.81 × 10 –3
650 1.49 × 10 –2
700 1.84 × 10 –2
720 1.98 × 10 –2

Note that the equilibrium constant increases dramatically with temperature. As a result, at equilibrium, thepressure of HImust also increase dramatically as the temperature is increased.

These data do not seem to have a simple relationship between K p and temperature. We must appeal to arguments based on Thermodynamics, from which it is possible to show that theequilibrium constant should vary with temperature according to the following equation:

K p Δ H ° R T Δ S ° R

If Δ H ° and Δ S ° do not depend strongly on the temperature, then this equation would predict a simple straight line relationship between K p and 1 T . In addition, the slope of this line should be Δ H ° R . We test this possibility with the graph in [link] .

Inverse of temperature vs. natural log of equilibrium constant

In fact, we do observe a straight line through the data. In this case, the line has a negative slope. Notecarefully that this means that K p is increasing with temperature. The negative slope via [link] means that Δ H ° R must be negative, and indeed for this reaction in this temperature range, Δ H ° 15.6 kJ mol . This value matches well with the slope of the line in [link] .

Given the validity of [link] in describing the temperature dependence of the equilibrium constant, we can also predict that anexothermic reaction with Δ H ° 0 should have a positive slope in the graph of K p versus 1 T , and thus the equilibrium constant should decrease with increasing temperature. A good example of an exothermic reaction is the synthesis of ammonia for which Δ H ° -99.2 kJ mol . Equilibrium constant data are given in [link] . Note that, as predicted, the equilibrium constant for this exothermic reaction decreases rapidlywith increasing temperature. The data from [link] is shown in [link] , clearly showing the contrast between the endothermic reaction and the exothermic reaction. Theslope of the graph is positive for the exothermic reaction and negative for the endothermic reaction. From [link] , this is a general result for all reactions.

Equilibrium constant for the synthesis of ammonia
T (K) K p
250 7.8 × 10 8
298 6 × 10 5
350 2 × 10 3
400 36

Inverse of temperature vs. natural log of equilibrium constant

Observation 4: changes in equilibrium and le châtelier's principle

One of our goals at the outset was to determine whether it is possible to control the equilibrium whichoccurs during a gas reaction. We might want to force a reaction to produce as much of the products as possible. In the alternative, ifthere are unwanted by-products of a reaction, we might want conditions which minimize the product. We have observed that theamount of product varies with the quantities of initial materials and with changes in the temperature. Our goal is a systematicunderstanding of these variations.

Questions & Answers

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 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
How can I make nanorobot?
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
how can I make nanorobot?
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.
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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
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