Questions tagged [kinetics]

The study of rates and steps in mechanisms of chemical processes.

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Difference between pre-equilibrium and steady-state approximation?

Both are reaction mechanisms in which there are several steps and at least one intermediate present. However, I am confused about the differences of both methods, especially when using them to ...
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Multiple choice question involving unimolecular reaction of diatomic species

For a unimolecular surface reaction involving a diatomic molecule, if transition state theory is applied, the following statement(s) is (are) true a. The rate will be proportional to $T^{3/2}$ b. q ...
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Can we say equilibrium is a process of separation of high energy and low energy particles?

Considering example of water and ice equilibrium we see that at molecular level the high energy particles (who have high kinetic energy) in ice gets converted to water and low energy particles in ...
4 votes
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Using a Chi-Square distribution table to calculate fraction of gas molecules with activation energy

I couldn't decide whether to ask this to Chemistry, Physics or Statistics stack exchange. Hopefully I made the right choice. According to this Wikipedia page, while the speed of particles in an ideal ...
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How to compute the ionic strength for a mixture?

Am I correct in thinking that if I wanted to find the ionic strength of a solution I would have to consider the concentration of EVERY ion in solution?
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Finding the Equilibrium constant of the iodine clock experiment

I know that the equilibrium constant can be found by using the intercept of the ln(rate) vs ln[concentraion] graph but is there another more reliable way of finding it?
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Mechanism of decomposition of N2O5

In my book mechanism of decomposition of $\ce{N2O5}$ was given like \begin{align} \mathrm{Reaction:}\\ \\ \ce{2 N2O5 &-> 4 NO2 + O2}\\ \\ \mathrm{Mechanism:}\\ \\ \ce{N2O5 &<=>[k_1][...
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States of matter - kinetic energy - intermolecular forces [closed]

My question is about the things that determine the state of the matter. I have been searching for a while now and some sites say that: both kinetic energy and intermolecular forces determine the ...
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Rate of Reaction and half life [duplicate]

During the course of chemical kinetics while studying zero order or first order they consider rate of reaction to be dependent only on single Reactant For ex:- A--> product,Rate of Reaction=k[A]^0 ...
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The differential rate law applies to only one single species

In my book it was written that The differential rate law applies to only one single species, so unless we have equimolar amounts of each reactant or make an approximation using an excess of one, we ...
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Can a non-rate determining step control what products form in a reaction?

In Organic Chemistry by Clayden, the stereoselectivity and regioselectivity of the E1 mechanism is explained in terms of the differing transition state energies (and therefore rates) of the possible ...
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Reversible monomolecular reaction with two reverse rates

I think this is a simple problem but my kinetics are terrible and I was hoping for some assistance following up on the work of a previous student. I'm open to any form of assistance and I hope this ...
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Concentration dependence of electron transfer

Regarding a single electron transfer: $$O +e^- \rightarrow R$$ We find the current dependent on the overpotential as specified by the Butler Volmer equation: $$i = i_0 (exp(\frac{\eta}{b})-exp(\frac{-\...
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Calculating rate constant for reaction between ethyl acetate and sodium hydroxide

My research question is investigating how temperature affects the rate constant for the reaction between ethyl ethanoate (acetate) and sodium hydroxide. I understand that I must titrate sodium ...
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Finding a Heterogeneous Catalyst for Hydrogen Peroxide

I'm designing an experiment to test the effect of surface area of a catalyst on the activation energy of hydrogen peroxide decomposition. However, I don't think I can use a powdered catalyst because ...
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Temperature dependence of order of reaction

In my textbook, it is given that the order of a reaction can change with temperature and pressure, but examples are not given. One possible explanation for this is that the rates of complex reactions ...
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Chemical kinetics for cyclic reversible reaction

Find $[\ce{C}]/[\ce{A}]$ for the following system at equilibrium: I know that at equilibrium $$\frac{[\ce{C}]}{[\ce{A}]} = \frac{k_{-3}}{k_3} = K_3, \tag{1}$$ but my teacher told me there was another ...
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What's the maximum temperature of quicklime slaking?

Normally the maximum temperature of lime slaking is listed at about 100 C. I've read that using water with high salt concentrations will catalyze the slaking reaction and increase the boiling point ...
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Crude palm oil DOBI analysis

I'm performing Crude Palm Oil DOBI spectrum analysis using uv-1900i UV-VIS spectrophotometer at a range of 269nm and 446nm but it's only giving peak absorbance at 446nm but no reading at 269nm,what ...
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2 answers
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chemical equilibrium and activity

Here is a graph of equilibrium coeff in various salt concentrations in water. Lets take the example $\ce{BaSO4}$. Now as we are increasing the salt concentration in water, the following reaction is ...
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Relation between activation and threshold energies

Activation energy $E_\mathrm{a}$ and threshold energy $E_0$ appear to be equivalent quantities: In particle physics, the threshold energy for production of a particle is the minimum kinetic energy a ...
3 votes
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What is the difference between a single displacement reaction and a two competing reaction system?

For example, consider the single-displacement reaction $$\ce{AB + C <=> BC + A}$$ My question is then if writing this reaction as the system \begin{gather} \ce{AB <=> A + B} \\ \ce{B + C &...
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Dependence of rate on the nature of reactants and other factors

Consider a reaction $$\ce{aA + bB -> cC + dD}$$ whose reactants are given by A and B and the products are C and D. The rate of this reaction is given by $$\frac{dx}{dt} = -\frac{d[\ce{A}]}{adt}= -\...
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How do I interpret the dissolution rate unit? [closed]

I have found a paper (link) that is interesting for my research project. The dissolution rate unit in this paper is described as $\pu{mol/cm^2/s}$. For my project I would need the dissolution speed ...
4 votes
3 answers
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Excited states and emission lifetimes

I have some doubts about the nomenclature of the lifetimes. Are singlet and fluorescence lifetimes the same? As well as the triplet and phosphorescence lifetimes? Also, can the triplet/phosphorescence ...
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Why can we use the arrhenius equation to measure the number of vacancies in a material?

In a materials science video I was watching today the prof. said we could use the arrhenius equation to estimate the number of vacancy point defects in a material. And gave the following equation: Nv =...
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Definition of activation energy

There seems to be contradictions in the definitions of activation energy ($E_a$) stated by different sources. I found two such popular definitions. Before that, I state my understanding of how an ...
4 votes
1 answer
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Oscillating vs Autocatalytic reactions

Are all oscillating reactions autocatalytic? Or are all autocatalytic reactions oscillating? What's the relation between them? Am I just mixing up different things or are they basically the same? For ...
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Exception to the order reaction and stoichiometric coefficient equality in elementary reactions

When a reaction is elementary,the stoichiometric coefficients always equal the order for each reactant? Is there any exception? Because at Ángel González Ureña's Cinética Química it says that this is &...
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1 answer
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Total vs. Partial derivatives in kinetics

I've recently seen partial derivatives in the velocity definition but in most cases is with total derivatives (infinitesimal change of concentration over infinitesimal change of time). Maybe is more ...
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Half-life vs. relaxation time vs. average lifetime

On page 25 of Ángel González Ureña's Cinética química (2001), appear the terms half-life time (of an intermediate) and relaxation time, but it refers to both of them with the letter $\tau$. Why is ...
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Why can't the half-life be determined in a reaction with more than one reactant?

We have a second order irreversible reaction with 2 reactants (A and B, order 1 for both) so that the initial concentrations are different. I've read that the half-life doesn't make sense in this ...
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How do we know that rates depend on the product and not the sum of reactant concentrations [closed]

I've been struggling to understand the mathematics behind the calculation in enzyme kinetics within systems biology at an intuitive level. Every research article and textbook says it is based on the ...
2 votes
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Differential equation in consecutive reactions

I'm blocked in a step of getting to the equation $(7)$, more precisely in the step between $(5)$ and $(6)$. I show my way to solve it down, but I don't get the same as $(6)$, so I wanted to know if I ...
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Iodine clock reaction: lower temperature but faster result?

I was told by several high school students that they experienced odd results in their iodine clock reaction lab. They did several different trials, and the lower the temperature, the faster the blue ...
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Mechanism of the blue bottle experiment

I have researched multiple mechanisms for this experiment yet all of them suggest different versions or are too vague. None of them are consistent since the final overall equation seems to be missing ...
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Negative or fractional order of reaction

Let $\ce{A}$ be the reactant and $\ce{P}$ the product at the imaginary elementary reaction $\ce{A->P}$. Could it possibly have a net total order of $-1?$ $$-\frac{\mathrm d[\ce{A}]}{\mathrm dt} = k[...
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Mathematical models of oscillatory chemical reactions

I am a mathematician working on real-life models in ordinary differential equations. I want to know if there are any models of oscillatory chemical reactions that consist of three ordinary ...
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How to compute backward reaction rate from forward one and an equilibrium data

Suppose we have have an ideal gas mixture and a reversible elementary reaction: $$ \ce{O + H_2 <=> H + OH} $$ Its forward reaction rate may be computed as follows: $$ \frac{d[\ce{H}]}{dt} = \...
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Half-life of a reversible first-order reaction of the form A ⇄ B

I am wondering if the half-life of a reversible first-order reaction of the form $\ce{A <--> B}$ is defined as the time in which half of the amount of reactant which should react up to ...
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Understanding uni- and termolecular reactions in combustion kinetics

I'm trying to understand and incorporate 9-species 19-reaction H2/O2 combustion mechanism into my numerical solver. The reaction mechanism in question is O'Conaire. It seems that the paper is in some ...
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Required induction time for steady-state approximation to hold

In chemical kinetics, since we often have to deal with complex reactions, approximations are introduced in order to make the calculations easier. A widely used simplification is the steady state ...
1 vote
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Serial reactions or consecutive reactions: rate vs time

Serial reactions, or consecutive reactions, are two or more reactions in which the product of the first reaction becomes the reactant in the next. The simplest case of a serial reaction involves a ...
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Rate law for thermolysis at temperatures well above the decomposition temperature

If the temperature is higher than the decomposition temperature, are thermal decomposition reactions reversible? For example, which of the following schemes would be more appropriate for temperatures ...
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Why don't we take activities in the rate law?

I am slightly confused by the fact that concentrations and not activities are taken in the rate law which is different to equilibrium and seems to lead to a discrepancy. For example, for the reaction $...
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How does the stoichiometric coefficient affect the time until a given percentage of the reactant is consumed (if at all)?

Problem from Serway's College Physics test bank: The reaction $2NO_2\rightarrow2NO+O_2$ obeys the rate law: $\large \frac{\Delta[O_2]}{\Delta t} = (1.40\times10^{-2})[NO_2]^2 \space at \space 500^\...
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How to rationalize independence of half-life time from the initial concentration for the first order reaction?

Using the rate expression for the first order kinetics and expressing the half-life time, it can be proven the half-life time $t_\frac 1 2$ of the first order reaction is independent of its initial ...
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How to rewrite kinetic mass balance to get to proper SI units?

Suppose from kinetic mass balance I get the following differential equation of the molarity substances $A$,$B$, and $C$ in a reactor, with molar in- or outflow rate $\phi$, and rate constant $k$: $$ \...
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Why doesn't molecularity ever exceed 3?

Recently, I learnt that molecularity of a reaction is limited to 3 and even that is quite rare. I searched online and asked my teacher about this but the explanation given was that it is difficult for ...
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2 votes
2 answers
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Does manganese reacts with water at "not" standard conditions?

In my answer, I stated that manganese is said to not react with water under normal conditions although some sources say it reacts with water to liberate hydrogen gas. Does it implies that it reacts ...
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