Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
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Approximating entropy change in a reaction using Arrhenius equation
I am a high school student.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 ...
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1answer
42 views
Kinetics of inversion of cane sugar
Question 1
The formula for concentration of cane sugar as a function of time is given by
$$k = \left(\frac{2.303}{t}\right) \log\left[\frac{\alpha(0) - \alpha(\infty)}{\alpha(t) - \alpha(\infty)}\...
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2answers
59 views
rate of reaction and RDS
An article on Khan-Academy, states the following:
The overall reaction rate is determined by the rates of the steps up to (and including) the rate-determining step
Here, it says that rate is ...
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0answers
39 views
Factors affecting rate of β-elimination reaction with alcoholic KOH
The question asks for the rate of reaction in $\beta$-elimination using alcoholic $\ce{KOH}$.
Arrange the following alkyl halides in decreasing order of rate of $\beta$-elimination reaction with ...
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2answers
83 views
What is the physical explanation driving current flow in a concentration cell?
In a galvanic cell, current is driven because the species at the cathode is reduced by grabbing some electrons from the cathode. The cathode now lacks electrons so it pulls them from the anode. Now ...
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Dependance of stability for reaction rate
In our book, it is given:
Organic compounds are generally less stable than inorganic compounds. Due to covalent bonding in them, their reaction rates are often slow.
First, it is said that they are ...
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1answer
64 views
Does rate of auto-ionization of water change after adding a strong acid?
We know that a reaction could have different rates at equilibrium. For example, lets take the reaction:
$$\ce{A + B -> C }$$
At equilibrium, the rates of formation and dissociation will be equal:
$$...
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0answers
24 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
39 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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1answer
41 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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2answers
129 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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1answer
60 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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2answers
58 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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0answers
26 views
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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0answers
39 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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1answer
66 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
56 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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0answers
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The interactions of the high energy gas particles
When we are talking about the idealization of the gas, why for high temperatures its particles interact less? I would say you have a bigger probability of the collisions among particles.
Quantum ...
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1answer
45 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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0answers
38 views
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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1answer
66 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
95 views
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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1answer
146 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[\...
2
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0answers
37 views
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
82 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
$$
\begin{cases}
\frac{\...
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1answer
60 views
Is the effect of hydroperoxyl radicals significant in the oxidation of organic compounds in the Fenton reaction? Why or why not?
In the Fenton reaction, a ferrous catalyst and hydrogen peroxide are used to generate hydroxyl radicals which in turn oxidise organic compounds. The reaction is commonly seen in the treatment of ...
5
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1answer
120 views
Nitrogen dioxide fluorescence quenching and lifetime
Nitrogen dioxide fluorescence quenching:
$$
\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} +...
2
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1answer
52 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
45 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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0answers
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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
91 views
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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0answers
48 views
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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0answers
23 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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0answers
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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 $\pu{150 ppb}$?
$$\ce{NH3_{(g)} + H2O_{(l)} &...
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What is the recipe for the Belousov-Zhabotinsky reaction for correct simulation with the Oregonator model? [closed]
For a school project I'm trying to model the Oregonator and perform some experiments with the Belousov-Zhabotinsky reaction. Like predicting the reaction and the swings in concentrations. For that it ...
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0answers
32 views
Production rate of parallel reactions
The degradation of hydrogen peroxide in water $\ce{(2 H2O2 (aq) → 2 H2O +O2 (g))}$ can be catalyzed by $\ce{Br-}$ and $\ce{H3O+}$. Derive an expression for the production rate for the following ...
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2answers
83 views
How to calculate the half time of a unimolecular reaction given the Arrhenius coefficient and the activation energy?
Consider the following unimolecular reaction:
$$\ce{H2O2 + M -> OH + OH + M}$$
The high pressure limit unimolecular rate coefficient for this reaction is $k_\mathrm{uni} = A\cdot \mathrm{e}^{...
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1answer
75 views
Find order of reaction 2A → B + C
Derive the integrated rate expression for a reaction of type:
$$\ce{2A -> B + C}$$
I first need to determine the order of the reaction in order to find integrated rate law of that particular order....
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2answers
76 views
How do we know a reaction is in equilibrium?
In teaching secondary science equilibrium, how can we actually show there is a backwards reaction occurring during equilibrium rather than no reaction. A lot of equilibrium experiments involve ...
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1answer
45 views
What is the rate expression for decomposition of $\ce{H2O2}$ in the presence of a catalyst?
What is the rate expression for decomposition of $\ce{H2O2}$ in the presence of a catalyst?
As far as I know for catalase, it is like this: $$\ce{Rate = k[H2O2][Catalase]}$$
I don't know what it is ...
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1answer
41 views
Does lower activation energy definitely mean higher rate?
Does lower activation energy definitely mean higher rate? For example the decomposition of $\ce{H2O2}$. Can we say it has the highest rate with the catalyst making the reaction's activation energy the ...
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3answers
86 views
How does the derivative of concentration make sense?
First of all, I would like to make clear that I don't know very much about chemistry, and I'm not very sure this is the right place on Stack Exchange for this question, so please let me know if it ...
5
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4answers
240 views
Why do so many biochemical reactions require enzymes?
Studying biochemistry as part of the Great Courses, I am struck that all 10 steps in glycolysis require an enzyme.
I’d have thought that evolution would have selected for a “simpler” pathway with ...
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1answer
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Conversion and reactor time [closed]
Lets say it takes my batch reactor 3 hours for 35% conversion.
If I wanted to find how long it would take for 15% then,
35-15 = 20,
then 3 hours/0.20 = 0.15 hours for 15% conversion.
I am not too ...
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0answers
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How to model the Belousov-Zhabotinsky (BZ) (in Maple) [closed]
I need to model the Belousov-Zhabotinsky reaction (or a different oscillating one). I found out about the Oregonator and the Brusselator reaction and now I want to model them in Maple (or similar ...
5
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1answer
57 views
Ammonia decomposition on platinum surface
I was given a problem I have to solve, unfortunately I cant wrap my head about it. I've searched the page for answers but they doesnt seem to fulfill my needs, so i'm asking for little guidance.
The ...
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1answer
51 views
what is the physical significance of ∆H=∆U for a chemical reaction?
In case of few chemical reactions $\Delta n=0$,so according to the equation $\Delta H= \Delta U+\Delta nRT$ change in enthalpy equals change in internal energy. But what does this in essence actually ...
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1answer
45 views
What you understand by “Order of reaction”? [closed]
When studying Kinetic chemistry (and most of the Physical chemistry topics), we often find definitions based upon the mathematical formalism. For example, Order of reaction is often defined as the sum ...
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1answer
39 views
When reactants are in their transition state, can they go back into their reactants form instead of progressing to form the products? [closed]
When reactants are in their transition state, can they go back into their reactants form instead of progressing to form the products? I don't see any reason why the reaction has to keep progressing ...
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1answer
62 views
Chemical equilibrium — why multiplication, rather than addition? [duplicate]
Why do we multiply (and not take the sum) the concentration of products and reactants when more than one entity is present in either side and rise the power to the coefficient term?
Suppose either
$$...
