Questions tagged [kinetics]

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

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Kinetics of Decomposition of Hydrogen Peroxide [duplicate]

Consider the decomposition of Hydrogen Peroxide: $$\ce{H2O2 -> H2O + 1/2O2}$$ The rate law for this reaction is : $$\text{Rate} = k[\ce{H2O2}]$$ Further $$\text{Rate} = -\frac{\mathrm d[\ce{H2O2}]}...
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Solving for Concentration Using pseudo-First Order Kinetics

The following graphs represent a pseudo-first order bi-molecular reversible reaction with the formula $\ce{A + B <=> C}$: The reaction product has an extinction coefficient of $\pu{50000 M-1 cm-...
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326 views

Meaning of Partial Half-Life for Two Parallel Reactions

Consider two parallel reactions: $$\ce{A -> B }\tag1$$ and $$\ce{A -> C}\tag2$$ What is the meaning of partial half life of the equation $(1)$ and that of equation $(2)$ with respect to ...
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Why is the units of rate constant dependent on the order of the reaction?

In many textbooks, it is written that For order (m + n), the rate constant, k has units of mol1−(m+n)·L(m+n)−1·s−1 However, by the Arrhenius equation, k can be expressed as k = PZexp(-Ea/RT) and ...
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338 views

Kinetics Vs Thermodynamics : Apparent contradiction in the definition of Enthalpy in the two disciplines

My book gives the following curve: It gives the following relation :$$ΔH= E_{\mathrm{activation,forward}}-E_{\mathrm{activation,backward}} \tag{1}$$ But I suspect that $ E_{\mathrm{activation,forward}...
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Arrhenius Equation : Interpretation

Consider the relation: $$E_{Activation}=E_{Threshold} - E_{Avg}$$ Here the $E_{Avg}$ refers to the Potential Energy of the reactants. Now in order of meet $E_{Threshold}$ , the molecules must have ...
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Arrhenius equation - Proper Interpretation of Activation Energy term

Consider the normal form of Arrhenius Equation:$$k=Ae^{-\frac {E_a}{RT}}$$ The term, $e^{-\frac {E_a}{RT}}$, is interpreted as the fraction of molecules having energy greater than Activation Energy. ...
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Inconsistency in Elementary Bi-Molecular Reaction Rate Expressions

Assume the following bi-molecular reaction is elementary as written with rate constant $k_\mathrm{f}$: $$\ce{A + A -> P}$$ This review, suggests to express the rate in terms of the production of ...
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How to determine rate law for a reaction?

I am having trouble understanding this problem. A proposed mechanism for the decomposition of $\ce{N2O5}$ is as follows \begin{align} \ce{N2O5 &->[$k_1$]NO2 + NO3} &&\text{(...
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Can a reaction have more than one rate determining step?

There are many organic reactions in which two steps have comparable rates. Can we say they are both RDS? For example, the rate of iodination of benzene and deuterated benzene is different even though ...
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161 views

Concentration and Half Life of reactants A and B

$3.12$ A reaction $\ce{A + B ->C}$, follows first order kinetics with respect to each reactant, with an overall rate constant $k=\pu{2.0 x 10^{-3} M-1s-1}$, the initial concentrations of A and B ...
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Arrhenius equation and rate constant

I am a high-school student and I am currently taking a course on chemical kinetics. Towards, what seems, end of the course at highschool level, the Arrhenius equation came in. Now, I'm not sure if ...
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284 views

Common Ion Effect - Ionic Equilibrium

Question In which of the aqueous solutions of the following, dissociation of $\ce{NH4OH}$ will be minimum? A) $\ce{NaOH}$ B) $\ce{H2O}$ C) $\ce{NH4Cl}$ D) $\ce{NaCl}$ My Thoughts My book says that ...
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Approximating entropy change in a reaction using Arrhenius equation

Recently my teacher finished teaching the chapter Chemical kinetics in which I have gone through Arrhenius equation.Can we estimate the change in entropy using it? I have done my calculation, ...
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339 views

Kinetics of inversion of cane sugar

Question 1 The formula for concentration of cane sugar as a function of time is given by $$k = \left(\frac{2.303}{t}\right) \log\left[\frac{\alpha(0) - \alpha(\infty)}{\alpha(t) - \alpha(\infty)}\...
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176 views

rate of reaction and RDS

An article on Khan-Academy, states the following: The overall reaction rate is determined by the rates of the steps up to (and including) the rate-determining step Here, it says that rate is ...
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198 views

Factors affecting rate of β-elimination reaction with alcoholic KOH

The question asks for the rate of reaction in $\beta$-elimination using alcoholic $\ce{KOH}$. Arrange the following alkyl halides in decreasing order of rate of $\beta$-elimination reaction with ...
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519 views

What is the physical explanation driving current flow in a concentration cell?

In a galvanic cell, current is driven because the species at the cathode is reduced by grabbing some electrons from the cathode. The cathode now lacks electrons so it pulls them from the anode. Now ...
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137 views

Does rate of auto-ionization of water change after adding a strong acid?

We know that a reaction could have different rates at equilibrium. For example, lets take the reaction: $$\ce{A + B -> C }$$ At equilibrium, the rates of formation and dissociation will be equal: $$...
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36 views

Catalysts and activation energy

Do catalysts increase rate of reaction only by decreasing activation energy? Or can they affect the Arrhenius factor or reaction orders? Like if one catalyst is more effective at increasing rate of ...
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1answer
370 views

Equilibrium constant for heterogeneous equilibria having aqueous as well as gaseous reactants

Suppose we have a heterogenous equilibrium : $$\ce{A(aq) +B(aq) <=> C(g) +D(aq)}$$ Which equilibrium constant is used here? Both pressure and concentration terms are there. So, according to me, ...
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87 views

Finding the ratio of rate constants [closed]

A group of mountain climbers set up a camp at a $\pu{3 km}$ altitude and experience a barometric pressure of $\pu{0.69 atm}$. They discover that pure water boils at $\pu{90 ^\circ C}$ and that it ...
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848 views

Finding time t in a first order reaction (JEE Adv 2019) [closed]

The decomposition reaction $\ce{2N2O5(g) ->[\Delta] 2N2O4(g) + O2(g)}$ is started in a closed cylinder under isothermal conditions at an initial pressure of $\pu{1 atm}$. After $\pu{Y \times 10^{3} ...
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117 views

Electrolysis of aqueous solutions

Water competes with any ions in solution for both oxidation and reduction. There are $1000\ \mathrm{g\ l^{-1}}/18\ \mathrm{g\ mol^{-1}}\approx55.56\ \mathrm{mol\ l^{-1}}$. That is truly huge in ...
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138 views

Half life of first order reaction in case of variable volume [closed]

I have a doubt about the meaning of half-life of a first-order reaction. Earlier I used to think that it is the time in which concentration of reactant reduces to half of its initial but recently I ...
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How can I analytically calculate the rate of thermal decomposition of calcium carbonate?

I am a first-time poster on Chemistry StackExchange, and not much of a chemist. I'm trying to determine the rate of thermal decomposition (in mol/s) of calcium carbonate ($\ce{CaCO3}$) at various ...
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160 views

Kinetics of Sabatier reaction

I am modelling a methanation process in MATLAB, where I have a rate equation for methanation $$\ce{CO2 + 4 H2 → CH4 + 2 H2O}$$ in which I need partial pressure of $\ce{CO2},$ $\ce{H2},$ $\ce{CH4},$ $\...
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83 views

How are half lifes calculated for radioactive substances that decay over many years [duplicate]

How are the half lives (or whole lives) calculated for slowly decaying radioactive substances such as tellurium? I must be having a fundamental misunderstanding of how we are able to predict the ...
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1answer
72 views

Finding the sensitivity of zero-order ultra sensitivity and its parameter dependence

I am provided a one-dimensional reaction system showing zero-order ultra sensitivity. $$\ce{X_1 ->[f_1] X_2}, \quad \quad \quad \ce{X_2 ->[f_2] X_1}$$ The reaction rate function is the reduced ...
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222 views

Why do isotopes have different chemical reaction rates? [duplicate]

Isotopes of a given element differ in the rates at which they undergo chemical reaction. Why is this so? The only explanation I could think of is that the gravitational force on the electrons ...
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Do tert-butylcyclohexanes with a leaving group locked in the equatorial position undergo E1?

Background Elimination of 1-bromo-tert-butylcyclohexane is a prototypical example of how important the anti periplanar relationship is for E2. From Organic Chemistry: Structure, Mechanism, Synthesis ...
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305 views

Chain transfer agents and rate of free radical polymerization

In free radical addition polymerizations sometimes chain transfer agents are added. From what I understand chain transfer agents (e.g. XR' below) reduce the average molecular weight by transferring ...
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1answer
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Half-life and shelf-life of second-order reaction

For integrated rate laws, I have attempted to find the shelf-life and half-life of second-order reaction: However, the answers I have obtained (which are labelled with a red cross) are very different ...
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257 views

Why does a first order reaction only depend on the concentration of a single reactant?

I am new to kinetics so please explain it from basic, If there is a reaction - $$\ce{A + B + C -> D}$$ In first order reaction rate is given by- $\mathrm R = k[\mathrm A]$ or $\mathrm R = k[\...
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Can the Belousov-Zhabotinsky reaction be simulated with the Brusselator?

I'm trying to simulate the Belousov-Zhabotinsky reaction mathematically, with a system of ODEs. I know how to do this with the Oregonator and now I'm looking for another model to simulate the BZ-...
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1answer
119 views

Example of chemical reaction with a given form for the kinetic equations

I’m an applied mathematician looking for examples from various applications fields (right now, chemistry, obviously) to illustrate the following reaction-diffusion system $$ \begin{cases} \frac{\...
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107 views

Is the effect of hydroperoxyl radicals significant in the oxidation of organic compounds in the Fenton reaction? Why or why not?

In the Fenton reaction, a ferrous catalyst and hydrogen peroxide are used to generate hydroxyl radicals which in turn oxidise organic compounds. The reaction is commonly seen in the treatment of ...
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1answer
149 views

Nitrogen dioxide fluorescence quenching and lifetime

Nitrogen dioxide fluorescence quenching: $$ \begin{align} \ce{NO2 + h\nu &->[$\varphi_\mathrm{Ia}$] NO2^{\ast}}\tag{I}\\ \ce{NO2^{\ast} &->[$k_2$] NO2 + h\nu'}\tag{II}\\ \ce{NO2^{\ast} +...
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71 views

Where does the RT term come from in the derivation for the activation enthalpy from the Eyring equation?

It is easy to show an Arrhenius-like equation from the Eyring equation, but if you do this, you get that the activation energy is about equal to the activation enthalpy. However, the real ...
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1answer
52 views

Rate law of reactions, what about the proportions? [closed]

Consider the reaction $$\ce{A + B + C -> D + E}$$ and $\mathrm{rate} = k[\ce{A}][\ce{B}]^2.$ My book said if we double the amount of $\ce{A},$ then the reaction rate will double. I understand ...
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42 views

Mass Transport and Ion Transport - Li-ion Batteries

I am new to the field and trying to grasp the theories/ physical phenomena behind the Li-ion batteries. I came across two phenomenons 'Mass transport' and 'Ion transport'. As I understood Mass ...
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4answers
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Determining Half-lifes from a graph

So I was studying for an exam I have thursday when I came across a question regarding half-life. I had previously thought that the definition of a half-life is the time it takes for the amount of ...
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Can a catalyst appear in the rate equation? [duplicate]

According to Wikipedia: Chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway with a lower activation energy than the non-...
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185 views

Are SN1 reactions pseudo unimolecular first order reactions?

I believe the the Solvent (present in excess) helps in ionisation of R-X to carbocation in Rate Determining step so shouldn't the Rate Determining step be a pseudo-unimolecular reaction as 2 molecules ...
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The pH of a drop of water containing ammonia

Presented with the following equations: What would the $\mathrm{pH}$ of a drop of water be, while in equilibrium with $\ce{NH3(g)}$ at a concentration of $\pu{150 ppb}$? $$\ce{NH3_{(g)} + H2O_{(l)} &...
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496 views

What is the recipe for the Belousov-Zhabotinsky reaction for correct simulation with the Oregonator model? [closed]

For a school project I'm trying to model the Oregonator and perform some experiments with the Belousov-Zhabotinsky reaction. Like predicting the reaction and the swings in concentrations. For that it ...
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Production rate of parallel reactions

The degradation of hydrogen peroxide in water $\ce{(2 H2O2 (aq) → 2 H2O +O2 (g))}$ can be catalyzed by $\ce{Br-}$ and $\ce{H3O+}$. Derive an expression for the production rate for the following ...
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2answers
225 views

How to calculate the half time of a unimolecular reaction given the Arrhenius coefficient and the activation energy?

Consider the following unimolecular reaction: $$\ce{H2O2 + M -> OH + OH + M}$$ The high pressure limit unimolecular rate coefficient for this reaction is $k_\mathrm{uni} = A\cdot \mathrm{e}^{...
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Find order of reaction 2A → B + C

Derive the integrated rate expression for a reaction of type: $$\ce{2A -> B + C}$$ I first need to determine the order of the reaction in order to find integrated rate law of that particular order....
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217 views

How do we know a reaction is in equilibrium?

In teaching secondary science equilibrium, how can we actually show there is a backwards reaction occurring during equilibrium rather than no reaction. A lot of equilibrium experiments involve ...

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