Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
893
questions
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1answer
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Activation energy and degrees of freedom
According to the Arrhenius equation the rate of a reaction increases as at higher temperature a greater percentage of molecules have translational kinetic energy greater than or equal to activation ...
1
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1answer
21 views
Rate of change and kinetics order of reaction question
The rate of reaction is given by the following equation, where [Ker-S-S-Ker] is just the molecule being broken down and [RSH] is an abbreviation for thioglycolic acid
The thioglycolate is in large ...
-1
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0answers
5 views
Calculate the amount of time it would take for the concentration to decrease from 0.0650 M to 0.0200 M [closed]
Acetaldehyde, CH3CHO, decomposes by second order kinetics with a rate constant of 0.334 M-1s-1 at 500 degrees Celsius. Calculate the amount of time it would take for the concentration to decrease from ...
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0answers
32 views
How does the Maxwell-Boltzmann distribution curve change when the amount of molecules is halved? [closed]
I wonder how the Maxwell-Boltzmann distribution curve change when half the molecules are removed. I have known that energy becomes less compared to the activation energy, but I'm not sure why this ...
2
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0answers
36 views
Concentration of sulfur in turbid solution
I recently participated in an experiment where I need to calculated the reaction orders and the reaction constant of the reaction:
$$\ce{8 Na2S2O3(aq) + 16 HCl(aq) -> S8(s) + 8 SO2(g) + 16 NaCl(aq) ...
1
vote
0answers
29 views
when is a system of mass-action reactions guaranteed to satisfy detailed balance?
when does a system of mass-action reactions satisfy detailed balance for any non-zero choice of the rate constants?
consider a trivial example:
$X + Y \ce{<-->[k1][k2]} XY$
satisfies detailed ...
0
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0answers
30 views
Why are we finding the integrated rate law by starting with r=k[A]?
When deriving the integrated rate equations, we start off with r =k[A] for example, and then we do the whole integration thing to find an equation of [A] in terms of time. But why are we ingnoring any ...
3
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1answer
36 views
Role of catalyst in elementary reactions towards rate law
We do know that the concentration of a catalyst might affect the rate of reaction. But what if the catalyst is included in the rate law? For example,
$$\ce{O3 + M <=>[$k_1$][$k_{-1}$] O2 + O + M}...
1
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4answers
58 views
Confusion over the rate law
I am really confused about the rate law. From my understanding, the rate law gives an equation that tells us the rate of the disappearance of the reactants. So, for example, the rate law of the ...
0
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0answers
13 views
Determine the order of reaction [duplicate]
Is there any formula that can help determine the order of the reaction?
Cause my teacher told me to plot line chart. So, I am curious about another method that doesn't use line chart (like formula ...
0
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2answers
34 views
Can rate constant depend upon the concentration of reactants (or other species involved in the reaction)?
Transition state theory tells us that the rate constant of an elementary step is $$\ce{k_r=\frac{\kappa k_BT}{h}e^\frac{- \Delta G^\ddagger}{RT}}$$
where $\ce{\Delta G^\ddagger}$ is the activation ...
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1answer
762 views
Why is a third body needed in the recombination of two hydrogen atoms?
In the article Discuss. Faraday Soc. 1962, 33, 205, the authors say that in order to form molecular
hydrogen from collision to atom we need a third body to remove the excess energy. That is we have ...
0
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0answers
34 views
Rate expression with water as one of the reactants
When finding an equation for d[A]/dt from reaction mechanisms and $\ce{H2O}$ is a product/reactant, does $\ce{H2O}$ have to be included or left out like for equilibrium constant expressions?
For ...
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0answers
27 views
Is order defined for a reaction which does not follow power law dependence?
As per my knowledge , order of a reaction is the sum of exponents of all the terms in rate law of the reaction
But reaction which do not follow power law dependence , for example , formation of HBr , ...
0
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0answers
30 views
Parallel reactions for one product
For me it is clear how I could solved the kinetic of a parallel reaction like this
But, how can I solve if this would be the case:
Thanks in advance!
1
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2answers
43 views
Organic-catalysis microwaves [closed]
When we perform a organic reaction without any addtional catalyst except that the reaction is carried out under microwave condition we can accelerate this reaction in comparison with one under heating ...
2
votes
1answer
60 views
Rate law for A + B ā C ā P
I need some clarification for the following assignment:
Derive the rate law for
$$\ce{A + B -> C -> P}$$
when $\ce{A + B -> C}$ is the slowest step and very slow.
My understanding is $\ce{A ...
-3
votes
1answer
36 views
How does it affect the equilibrium expression if the concentration of any component remains the same?
I am a high school student and I am very confused in Equilibrium expression, My confusion is that "Why we don't write concentration of solids and pure liquids in equilibrium expression?" ...
0
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0answers
54 views
Is this statement valid for reactions of all orders? [duplicate]
My textbook (not an international standard) states that for the first order reactions only
The quantity of reactant remaining after $n$ half lives is
$$A_n = \frac{A_0}{2^n},$$
where $A_0$ is the ...
1
vote
0answers
33 views
Is it easier to mix a solution that is in the liquid or in the vapor phase?
In the article on dilution, Wikipedia has the following statement:
The same direct relationship applies to gases and vapors diluted in air for example. Although, thorough mixing of gases and vapors ...
2
votes
1answer
28 views
How do I compute the mean dissociation time from the dissociation constant, assuming instantaneous binding reaction rate?
There is a solution with two chemical species, A and B. Given the equilibrium dissociation constant
$
K_D=\frac{[A][B]}{[AB]}
$
how do I relate the mean dissociation time $t_{off}$ to $K_D$, and ...
1
vote
2answers
42 views
Can reversible reactions proceed by different mechanisms in the forward and reverse directions? [closed]
It seems odd to me that this would be the case, but it also seems odd that it wouldn't.
Imagine a mechanism for a (forward) reaction that includes a slow reversible step and a fast irreversible step:
...
0
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0answers
28 views
Brownian motion modeling of surface reaction
I am interested in simulating a reaction-diffusion system, where particles subjected to Brownian motion can react when they reach a specific surface. The reaction is simple:
A $\rightleftharpoons$ B
...
1
vote
1answer
21 views
how to derive equilibrium concentrations from initial conditions for mass action reactions?
I am reading a tutorial on biochemical reactions and mass action kinetics (https://www.math.utah.edu/~keener/books/control.pdf, pp. 1-2) and would like to derive an analytic solution to confirm ...
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votes
1answer
65 views
Wikiās explanation of the rate of chemical reaction [closed]
Could you please help me understand the Wikiās explanation of the rate of chemical reaction?
It says: the rate of the chemical reaction is directly proportional to the product of the activities or ...
5
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5answers
957 views
Does it make sense to differentiate the Arrhenius equation with respect to temperature?
I am trying to answer the question: "between concentration and temperature, which has a greater significance on the rate of reaction"
Hence, I'm trying to find a method to systematically ...
1
vote
1answer
62 views
Understanding transition state theory
Let's say we have standard chemical reaction given by
$$A-B + C \leftrightharpoons [A\cdot\cdot B\cdot\cdot C]^{\dagger} \rightarrow A +B-C$$
I want to estimate the pre-exponential factor of this ...
0
votes
1answer
85 views
Why does activation energy depend on temperature? [duplicate]
To me it makes sense that the activation energy $E_\mathrm a$, as given by the Arrhenius equation, doesn't depend on the temperature as the needed energy (potential energy) to start a reaction has ...
1
vote
1answer
140 views
Kinetics question regarding Rate Law
The acid catalysed hydrolysis of an compound $\ce{A}$ at $\pu{303K}$:
$$\ce {A ->[$k$] B}$$ has a half-life of $\pu{100 min}$ when carried out in a buffer solution of $\mathrm{pH=5}$ and $\pu{10 ...
1
vote
0answers
111 views
Deriving an expression for reaction time in terms of the total concentration
Consider the dimerization of protein $\ce{A}:$
$$\ce{2A <=> A2}$$
with forward rate constant $k_1$ and backwards rate constant $k_{-1}.$ Derive the following expression for the reaction time in ...
0
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0answers
43 views
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
$$\text{Rate} = -\frac{\mathrm d[\ce{H2O2}]}...
2
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0answers
30 views
Solving for Concentration Using pseudo-First Order Kinetics
The following graphs represent a pseudo-first order bi-molecular reversible reaction with the formula $\ce{A + B <=> C}$:
The reaction product has an extinction coefficient of $\pu{50000 M-1 cm-...
0
votes
1answer
75 views
Meaning of Partial Half-Life for Two Parallel Reactions
Consider two parallel reactions:
$$\ce{A -> B }\tag1$$
and
$$\ce{A -> C}\tag2$$
What is the meaning of partial half life of the equation $(1)$ and that of equation $(2)$ with respect to ...
3
votes
2answers
61 views
Why is the units of rate constant dependent on the order of the reaction?
In many textbooks, it is written that
For order (m + n), the rate constant, k has units of mol1ā(m+n)Ā·L(m+n)ā1Ā·sā1
However, by the Arrhenius equation, k can be expressed as
k = PZexp(-Ea/RT)
and ...
1
vote
1answer
323 views
Kinetics Vs Thermodynamics : Apparent contradiction in the definition of Enthalpy in the two disciplines
My book gives the following curve:
It gives the following relation :$$ĪH= E_{\mathrm{activation,forward}}-E_{\mathrm{activation,backward}} \tag{1}$$
But I suspect that $ E_{\mathrm{activation,forward}...
0
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0answers
49 views
Arrhenius Equation : Interpretation
Consider the relation:
$$E_{Activation}=E_{Threshold} - E_{Avg}$$
Here the $E_{Avg}$ refers to the Potential Energy of the reactants. Now in order of meet $E_{Threshold}$ , the molecules must have ...
0
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0answers
35 views
Arrhenius equation - Proper Interpretation of Activation Energy term
Consider the normal form of Arrhenius Equation:$$k=Ae^{-\frac {E_a}{RT}}$$
The term, $e^{-\frac {E_a}{RT}}$, is interpreted as the fraction of molecules having energy greater than Activation Energy.
...
0
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2answers
59 views
Inconsistency in Elementary Bi-Molecular Reaction Rate Expressions
Assume the following bi-molecular reaction is elementary as written with rate constant $k_\mathrm{f}$:
$$\ce{A + A -> P}$$
This review, suggests to express the rate in terms of the production of ...
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votes
1answer
176 views
How to determine rate law for a reaction?
I am having trouble understanding this problem.
A proposed mechanism for the decomposition of $\ce{N2O5}$ is as follows
\begin{align}
\ce{N2O5 &->[$k_1$]NO2 + NO3} &&\text{(...
1
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0answers
43 views
Can a reaction have more than one rate determining step?
There are many organic reactions in which two steps have comparable rates. Can we say they are both RDS?
For example, the rate of iodination of benzene and deuterated benzene is different even though ...
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votes
1answer
55 views
Concentration and Half Life of reactants A and B
Since reaction is first order with respect to both reactant A and B, I can write,
$$ k=\frac{1}{t} \ln{\frac{a}{a-x}}
$$
where a is initial concentration of reactant and a-x is remaining ...
0
votes
0answers
19 views
Doubt's regarding inputting surface reaction for Chemkin Pro
I want to simulate the reaction of a mixture of ethanol and Hydrogen Peroxide on $\ce{Pt}$ using Chemkin Pro. I want to create a surface input files which will include surface reaction mechanism of ...
1
vote
1answer
57 views
Arrhenius equation and rate constant
I am a high-school student and I am currently taking a course on chemical kinetics. Towards, what seems, end of the course at highschool level, the Arrhenius equation came in. Now, I'm not sure if ...
4
votes
1answer
171 views
Common Ion Effect - Ionic Equilibrium
Question
In which of the aqueous solutions of the following, dissociation of $\ce{NH4OH}$ will be minimum?
A) $\ce{NaOH}$
B) $\ce{H2O}$
C) $\ce{NH4Cl}$
D) $\ce{NaCl}$
My Thoughts
My book says that ...
2
votes
0answers
72 views
Approximating entropy change in a reaction using Arrhenius equation
I am a high school student.Recently my teacher finished teaching the chapter Chemical kinetics in which I have gone through Arrhenius equation.Can we estimate the change in entropy using it? I have ...
0
votes
1answer
81 views
Kinetics of inversion of cane sugar
Question 1
The formula for concentration of cane sugar as a function of time is given by
$$k = \left(\frac{2.303}{t}\right) \log\left[\frac{\alpha(0) - \alpha(\infty)}{\alpha(t) - \alpha(\infty)}\...
1
vote
2answers
90 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 ...
0
votes
0answers
76 views
Factors affecting rate of Ī²-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 ...
1
vote
2answers
120 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 ...
3
votes
1answer
93 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:
$$...
