The study of rates and steps (mechanisms) of chemical processes.

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Can there be more than one combination of reactant/product concentration for a specific equilibrium constant?

For an elementary reaction like $$\ce{A + B -> AB},$$ $$K_{c} = \frac{\ce{[AB]}}{\ce{[A][B]}}$$ and $$\frac{\mathrm{d}\ce{[AB]}}{\mathrm{d}t} = k\ce{[A][B]}.$$ If I let the reaction reach ...
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34 views

Why does radioactive decay occur?

Is there a reason radioactive decay is exponential, as in after an extremely long time some of the original compound remains, or is this just an empirical model? Also, why does $\ce{^{238}U}$ have a ...
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Iodine and persulfate kinetics: What can be deduced from graph?

From a graph of iodine concentration vs time of the reaction of iodide with persulfate, what can be deduced? Is it possible to find the order with respect to iodide and with respect to persulfate?
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Finding rate constant at different temperature

For the reaction $$ \ce{2N2O5(g) -> 4NO2 + O2(g)} $$ the rate law is: $$ \frac{\mathrm{d}[\ce{O2}]}{\mathrm{d}t} = k[\ce{N2O5}] $$ At 300 K, the half-life is 2.50·104 seconds and the activation ...
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How do I find the rate of the reaction?

If the concentration of Sodium thiosulfate is $\mathrm{0.1\ Mol\cdot L^{-1}}$ and the concentration of Hydrogen us $\mathrm{1.0\ Mol\cdot L^{-1}}$ and the reaction time is 42 seconds, will the rate ...
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What is the non-ideal equivalent of mass action kinetics?

Starting from the equations of mass action kinetics, one may show that (for suitably chosen numbers $A_i$), the function $\sum_i x_i(A_i + \log x_i)$ is a Lyapunov function, i.e. it decreases over ...
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12 views

Improving a mathematical model of a chemical reaction

I want to improve a mathematical model to suggest a rate expression. How can I do it by using relative absorbance values? The reaction is UV-catalyst decomposition. I don't know concentration values ...
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92 views

“There are no chemical cliffs”

Are there any reactions with no activation energies? Prof just told us there are no chemical cliffs. Is this true? I read something about nuclear decay as being a reaction with no activation ...
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63 views

Finding Root-Mean-Square of Ne using kinetic energy?

I am not being able to solve the following question: -Find the root-mean-square speed of $\ce{Ne}$ atoms at the temperature at which their kinetic energy is $\mathrm{6.24\ kJ/mol}$. I tried ...
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63 views

How can a catalyst not be included in a rate equation, if it by definition speeds up a chemical reaction?

I thought that anything not in a rate equation was automatically zeroth order and therefore did not affect the reaction? But I have heard that catalysts can be involved in a reaction while not being ...
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48 views

Radioactivity and Kinetics of disintegration

Well I've just started on kinetics and there are a few things I am absolutely confused about! First of all , is neutron actually made up of a proton and electron? if yes then how is it possible? In ...
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75 views

A few basic questions about activation energy and the Maxwell-Boltzmann distribution

I understand activation energy to be the relative difference in energy between that of the activated complex/transition state (at some temperature) and the average energy of the reactants like shown ...
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162 views

Oxidation of formate ion by peroxydisulfate in water solution: Why are there “strange” kinetics?

As you can see, the first step is the slowest, but by using the rate-determining step approximation you wouldn't arrive at the correct rate law which is: $r=k\ce{[HCOO^{−}]}^{1/2} ...
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27 views

Rate law and rate constant [closed]

How do we obtain the expressions for integrated rate laws ?!? What are the limits we integrate it under and with respect to what do we integrate it?
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39 views

Reversible elementary reaction

I have a question regarding a reversible elementary reaction: If we have an equilibrium where $$\ce{A<=>[k_1][k_{-1}]B}$$ , then $$-d[A]/dt= k_1[A]-k_{-1}[B]$$. If we take $$[B]=[B]_0 + ([A]_0 ...
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44 views

Significance of Kinetic Velocities?

In the concept of Kinetic Molecular Theory we have rms(root mean square), avg(average) and mp(most probable) velocities. I understand the concept well. But my question is why do we have three ...
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52 views

Molecularity vs Order Of Reaction

In the field of Chemical Kinetics, terms like Molecularity and Order Of Reactions are often used. I am a bit confused between these two terms. Can someone explain to me about these two terms and ...
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70 views

What is the constant of integration in a series reaction in chemical kinetics?

I have a question regarding the rates for a series reaction in kinetics. So imagine $\ce{A -> B -> C}$, with $k_1$ as rate constant for $\ce{A -> B}$ and $k_2$ as rate constant for $\ce{B ...
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568 views

Why is proton transfer so fast?

Why is proton transfer always kinetically favored? In other words, why are Bronsted acid-base reactions so quick? Is it because protons are generally unhindered, sterically? This seems plausible; ...
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55 views

Formation of 2,4-Dichlorophenol by free chlorine mediated oxidation of Triclosan

I cannot find much guidance in the literature. This is the reaction between free chlorine in water and triclosan. I understand ether cleavage and electrophilic aromatic substitution (maybe) involved. ...
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82 views

Rates of reaction

Assume a reaction is of second order kinetics and that the rate constant is k. The differential rate equation is given by: A+B->Products -dCa/dt = kCaCb Show that the general expression of ...
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Can in any case the faster step of the reaction be rate determining?

I found a sentence in book which states the reverse step of this reaction ( I forgot what was it!) has the faster step as rate determining . Even Rate determining step-Wikipedia states: In ...
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124 views

Determining exponents in a rate law with different data

Here is the experimental data: Note all concentrations are the initial amounts \begin{array}{cccc} \text{Experiment} & \ce{[C_{2}H_{4}Br_{2}]} &\ce{[I^{-}]} & \text{Initial rate of ...
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71 views

Show proposed mechanism is consistent with the experimental rate law

The mechanism for the reaction: \begin{align} \ce{NO_{(g)} + O_{2(g)} &<=>[k_{-1}][k_{1}] NO_{3(g)}} &\text{(fast)}\\ \ce{NO_{3(g)} + NO_{(g)} &<=>[K_{2}] 2\,NO_{2(g)}} ...
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312 views

Why are methanol flames less visible than other flames?

The combustion of methanol tends to generate flames that are less visible than the flames generated by the combustion of other substances? My guess is that methanol burns quickly as it has a ...
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34 views

Where can I find Equilibrium Constants?

When trying to develop mathematical models to show the concentration in a reaction, where can one find a database or good source of known equilibrium constants if it is not necessarily very convenient ...
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57 views

Can a multi-species system oscillate around equilibrium?

In reading about chemical oscillations such as those that occur in the Belousov–Zhabotinsky reaction (BZ), it's often reported that these reactions were initially not taken seriously, because of a ...
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80 views

Rate-determining step and steady state approximation failure

1) When can't the rate-determining step be applied, and why? How do you recognize these cases? 2) When can't the steady state approximation be applied, and why?
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68 views

What is the correct definition of the Gibbs free energy of activation?

Is the following correct? Gibbs free energy of activation is used in energy profiles where the stabilities of the species are expressed as changes in Gibbs energy, while the activation energy Ea ...
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26 views

Analytically combining Dynamic Equilibria that have a two way affect?

Lets say I want to model a water system as the following set of equilibria: $\ce{H2O <=> OH- + H3O+}$ | $\ce{A=[OH^{-}][H3O+]}$ $\ce{CO2 + H2O <=> H2CO3}$ | ...
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102 views

Why is the equilbrium constant expressed the way it is?

Why are the two molarity's multiplied and not added and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply ...
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111 views

Rate-limiting in transition state theory

Suppose an initial state $A$ can transition to either state $C$ or state $D$. Suppose further that both of these two processes are rate-limited by a transition to the same intermediate state $B$, as ...
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Relationship between rate equation and equilibrium constant

I have read mannaia's answer on the question of 'rate order and confusion', as well as Nicolau Saker Neto's answer to a related question. They have both been very helpful. As I understand, the ...
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145 views

Kinetic and Thermodynamic Stability

My prof noted that if the two components of any ionic compound undergo a large extent reaction with each other, then the substance CANNOT exist as a pure substance. For example, consider ammonium ...
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41 views

Formation Constants; Lewis Acidity

I still distinctly remember reading about how Lewis acidity/basicity was characterized using kinetics. The reason given was that because formation constants are so large, these reactions are not ...
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43 views

What are the units for m in the average kinetic energy formula?

For the equation $E_k=\frac{1}{2}mu^2$ what does the $m$ variable represent? I would say mass but the textbook does not say explicitly that it is anything.
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What is reactivity really, and can it be quantified?

I understand the concept of a reactive species on a sort of vague and intuitive level: a reactive species is one that has lots of reactions that it can participate in. These tend to have large kinetic ...
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87 views

Plot of Arrhenius Equation with temperature

I saw the plot of Arrhenius Equation Here It is a concave upwards graph, but acc to the equation $k= A e^\frac{-E_a}{RT},$ it is evident that the graph is of the form $y= e^\frac{-1}{x}.$ I ...
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286 views

Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

Take for instance the rection $$\ce{H2(g) + I2(s) -> 2HI(g)}$$ The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a constant, ...
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Finding overall order of reaction

Recently I've been going through an exercise of Chemical Kinetics and Nuclear Chemistry and right now I am stuck to one. Question was previously asked in JEE(Advanced)-2013. The question says, In ...
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67 views

Activation Energy in Acid/Base reactions

For simple acid/base reactions - i.e. those involving inorganic compounds - does activation energy ever play in reactions? Or can we ignore kinetics entirely and just consider thermodynamic factors ...
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66 views

Does this activation of carbonyls usually involve a SN1 or a SN2?

The process I have seen in class to activate a carbonyl function is acetalisation. One of the steps involved is the following : So I was wondering, is that a $\ce{S_{N}1}$ or a $\ce{S_{N}2}$ ? ...
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Furan and maleic anhydride: Why is the major product exo?

For most Diels-Alder reactions, the product is endo because there are favorable interactions between the newly forming pi-bond and the electron withdrawing groups of the dienophile. Why is the ...
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63 views

Rate law of the iodine clock reaction

I am dealing with the iodine clock reaction, which has the half-reactions: $$\begin{align}&\ce{H_2O_2 (aq) + 2I^- (aq) \to I_2 (s) + 2 OH^- (aq)} & (\text{slow}) \\ &\ce{I_2 (s) + ...
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71 views

Variation of Arrhenius equation with concentration

In the Arrhenius equation do Arrhenius constant and activation energy depend on concentration ? (Their units do)
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Should binding constants be unitless when deriving fractional occupancy equations from reactions?

It is known that binding (aka association) constants are in fact unitless, as has been discussed here already. However, I'm not a chemist and am confused about when one should or should not use units ...
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Will heating diatomic oxygen enough break the O=O bonds?

The bond enthalpy associated with a O=O double bond is equal to 495kJ/mol. Does that mean that adding enough kinetic energy in the form of heat will eventually cause the bonds to break and create ...
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Does a first order reaction really get completed only at infinity?

We know for a $1^{\text{st}}$ order reaction $ A \rightarrow B$, we write the rate law as: Rate = $k[A]^{1}$, and the integrated law for this is $ \ln (\frac{A}{A-x}) = kt$. So by studying this ...
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Magical reaction tanks

I would be interested to know people's opinion on the following matter. Background Often, when the far-from equilibrium behaviour of a chemical reaction system is analysed mathematically (in papers ...
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Relationship between magnitudes of forward and reverse kinetic rate constants

Consider the reversible unimolecular reaction: $A \overset{k_{1}}{\underset{k_{2}}{\rightleftharpoons}} B$ We know that the forward reaction is often considerably more thermodynamically favourable ...