# 0.19 Reaction kinetics  (Page 3/7)

 Page 3 / 7

As a cautionary note, the results from the previous Concept Development Study make it clear that not every rate law is as simple as the one for the reaction of O 3 with Cl. We will return to this topic in a later section.

## Observation 2: temperature dependence of reaction rates

How is the effect of temperature change on the reaction rate reflected in the rate law equation? Recall that a rate law shows the dependence of the reaction rate on reactant concentrations, e.g. the rate of reaction of I 2 gas with H 2 as described in Equation (3) gas is given by the rate law in Equation (4).

H 2 (g) + I 2 (g) → 2HI(g)

Rate = k[H 2 ][I 2 ]

One possibility for the increase in the rate of this reaction when temperature is increased is that there is a slight dependence on temperature of the concentrations, since volumes do vary with temperature. However, this is insufficient to account for the dramatic changes in rate typically observed. Therefore, the temperature dependence of the reaction rate is primarily found in the rate constant, k . The rate constant of this reaction at each temperature can be found using the Method of Initial Rates, as discussed in the previous study, and we find in Table 1 that the rate constant increases dramatically as the temperature increases.

T(K) k (1/M∙sec)
667 6.8×10 -3
675 9.87×10 -3
700 3.00×10 -2
725 8.43×10 -2
750 2.21×10 -1
775 5.46×10 -1
800 1.27

As shown in Figure 1, the rate constant appears to increase exponentially with temperature. After a little experimentation with the data, we find in Figure 2 that there is a simple linear relationship between ln( k ) and 1/T.

From Figure 2, we can see that the data in Table 1 fit the equation

ln (k) = a $\frac{1}{T}$ + b

where a and b are constant for this reaction. It turns out that, for our purposes, all reactions have rate constants that fit Equation (5), but with different constants a and b for each reaction. Figure 2 is referred to as an Arrhenius plot, after Svante Arrhenius.

It is not obvious why this equation should work for every chemical reaction. When we remember that the temperature is related to energy, it would seem that exothermic reactions and endothermic reactions should have different temperature dependence. Since they do not, this suggests that temperature increases and corresponding energy increases are not connected to the overall energy change of a reaction. This will lead us to a model to account for the temperature dependence of the rate constant. We will develop this further later in the next section.

## Observation 3: activation energy

Equation (5) is very convenient for describing the temperature dependence of a reaction. However, we would like some insight into why the temperature dependence should obey Equation (5), and in particular, into the meaning of the constants a and b in the equation.

As noted at the end of the last section, Equation (5) describes the rate constant temperature dependence regardless of whether the reaction is endothermic or exothermic. Therefore, whatever the energetic factor is that is required for the reaction to occur, it is not just that the reaction is endothermic. Exothermic reactions apparently require energy as well. It must be that all reactions, regardless of the overall change in energy, require energy to occur.

#### Questions & Answers

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
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why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
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it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
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Anassong
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there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
how did you get the value of 2000N.What calculations are needed to arrive at it
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