Questions tagged [kinetics]

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

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1answer
398 views

p-Nitroaniline reaction with sulfuric acid

An alternative version of the well-known demonstration carbon snake (the dehydration reaction of sugar by concentrated sulfuric acid forming a column of graphite) consists in mixing paranitroaniline ...
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Hydrogen peroxide and potassium iodide reactions

What is the explanation for the two possible reactions of $\ce{H2O2}$ with $\ce{KI}$ in acid media (iodide-catalyzed decomposition of hydrogen peroxide or iodide oxidation by hydrogen peroxide) and ...
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Normalising Kinetic Isotope Effect Per Deuterium Atom

I've synthesised a protic and deuterated version of a specific molecule where there are two deuterium atoms in the latter. I then go about and measure the kinetic isotope effect (KIE) for a reaction ...
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Differences in AChE inhibition kinetics between VX and VR

According to the referenced paper, VR has an AChE inhibition reaction rate constant almost 4 times that of VX. Interestingly, its reaction rate constant for aging of the enzyme is less than that of VX,...
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2answers
436 views

Why does denaturation of albumen protein cause pH of solution to increase?

I'm interested in the denaturation of proteins by alcohols, specifically by ethanol. I have devised a simple experiment in which I inject solutions of ethanol (of variable concentrations) into ...
4
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1answer
98 views

Propagating uncertainty with the slope of a tangent line

I have done an experiment that found the initial reaction rate for a reaction that created gas in $\pu{kPa s^-1}$ by finding the slope of the tangent line at time = 0. How do I propagate uncertainty ...
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4answers
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Formula for rate constant for the first order reaction

My lecturer mentioned that the formula for the rate constant $k$ for the first order reaction is $$k = \frac{2.0303}{t_{1/2}}\,\log\frac{[\ce{A}]_0}{[\ce{A}]_{t_{1/2}} - [\ce{A}]_0},\tag{1}$$ where $...
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51 views

Finding rate constant from a change in pressure experiment

I measured the change in pressure for the decomposition of hydrogen peroxide in the presence of a manganese(IV) oxide catalyst at 5 different temperatures: $$\ce{2 H2O2 (l) ->[MnO2 (s)] O2 (g) + 2 ...
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Is it feasible to calculate the rate law of the oxidation of ethanol using colorimetry?

My IB Chemistry class needs to have our Internal Assessment ideas finalized by next week, and I'm torn between a few experiments. I'm considering performing an oxidation of ethanol and potentially ...
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80 views

What happens when solution containing two or more cations are electrolysed at an excess potential?

$\pu{250 mL}$ of a waste solution obtained from the workshop of a goldsmith contains $\pu{0.1 M}$ $\ce{AgNO3}$ and $\pu{0.1 M}$ $\ce{AuCl}$. The solution was electrolyzed at $\pu{2 V}$ by passing a ...
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Steady State: Exclusion of Term

Synopsis We are given a proposed mechanism for the condensation of $\ce{(CH_3)_2CO}$ as follows First Step: $$\ce{(CH_3)_2CO + OH^- <=> CH_3C(O)CH_2^- + H_2O}$$ Second Step: $$\ce{CH_3C(O)CH_2^- ...
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1answer
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Activity of Polonium in half-time in Becquerels

I got an exercise but I don't know the exact answer. In the catalog note of the reference source of Polonium-210 radiation with a half-life of 138 days, it was stated that one day the activity was $\...
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1answer
153 views

Why a catalyst is not consumed in a reaction when all steps are reversible?

It is said that a catalyst speeds up the rate of a reaction but is not consumed (assuming no side reactions take place). Suppose we have the following reaction: $$\ce{A + B <=> C} $$ catalysed ...
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1answer
257 views

Equilibrium constant of a reaction whose order of forward and reverse reaction is not same

Suppose, a reaction is like, $$\ce{aA + bB <=> cC + dD}$$ and that A, B, C, D all are gas. Now it is known that: $$K_c = \dfrac{[A]^a[B]^b}{[C]^c[D]^d}$$ Now if the forward reaction is second ...
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1answer
98 views

Why does chemisorption decrease with increasing temperatures?

Why is it that chemisorption decreases with higher temperatures? The explanations I found online were quite vague and one of them cited Le Chatelier's principle, but I thought chemisorption is an ...
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53 views

Is standard change in activation Gibbs free energy indepedent of pressure?

For a chemical reaction the activation volume is defined as: $$Δ^{\ddagger}V={V^\ddagger}-V$$ where both $V^\ddagger$ and $V$ refer to standard states (I have omitted the symbol for simplicity). One ...
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1answer
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kinetic description of an autocatalytic system

I have previously asked this question at physics SE here and it was suggested to post it here. I am looking at the system: $2X + Y \Leftrightarrow 3X $ $A \rightarrow Y$ $X \rightarrow B$ The ...
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1answer
89 views

Why are the "extents of reaction" the same for all reactants and products?

Consider the follwoing reaction: $$\ce{a A + b B -> c C + d D}\tag{1}$$ where $\ce A$ and $\ce B$ are the reactants, $\ce C$ and $\ce D$ are the products, and $a (<0)$, $b(<0)$, $c(>0)$, ...
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1answer
216 views

New relationship between exponential factors and entropy of a reaction?

Consider the reaction $\ce{A <=> B}$. Let $k_f$, $E_A$, and $A$ denote the forwards rate constant, activation energy, and pre exponential factor, respectively. Let $k_r$, $E_A'$, and $A'$ denote ...
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Reversible equation in Chemical Kinetics — Should I use definite integral when solving the differential equation?

I found this problem: We have the following reversible reaction: $A \ce{<=>[\ce{k_1}][\ce{k_2}]} B $, described by the kinetics equation: $$\frac{d[X]}{dt} = k_1([A]_0-[X])-k_2([B]_0+[X])$$ ...
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Getting close to zero percent of particles with energy greater than an activation energy of 101kJ/mol using the Maxwell-Boltzmann energy distribution

I experimentally obtained the activation energy of a reaction to be approximately 101kJ/mol. I was then going to use the value for the activation energy to see how the number of particles with ...
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36 views

Determine the rate law for the given reaction

I was studying for a PhD entrance exam and this question made me wonder about some topics in kinetics: Consider the multi-step reaction below: $\ce{A_2 → 2 A}$ $\ce{2A + X → Y + B}$ $\ce{B → A2 + Z}$ ...
3
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1answer
132 views

Relationship between molecularity and the reaction order

Should the molecularity be equal or less than the reaction order? Consider the reaction: $$\ce{H2(g) + I2(g) → 2 HI(g)}$$ If we consider the mechanism of this multi-step reaction, the molecularity is ...
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1answer
150 views

Frequency Factor of the Arrhenius Equation

The question came to my mind as to whether the effect of a catalyst on a reaction included the modification of the frequency factor (or pre-exponential factor) of a reaction, shown in Arrhenius' ...
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1answer
153 views

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 ...
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1answer
25 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 ...
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40 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) ...
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30 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 ...
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34 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 ...
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1answer
81 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}...
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4answers
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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 ...
3
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1answer
199 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 $$k_\mathrm{r} = \frac{\kappa k_\mathrm{B}T}{h}\exp\left\{\frac{- \Delta G^\ddagger}{RT}\right\},$$ where $\Delta G^\...
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1answer
828 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 ...
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64 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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28 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 , ...
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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!
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2answers
51 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 ...
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1answer
88 views

Rate law for A + B → C → 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 ...
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1answer
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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?" ...
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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 ...
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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 ...
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1answer
35 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 ...
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2answers
101 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: ...
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1answer
28 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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1answer
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Wiki’s explanation of the rate of chemical reaction [closed]

Could you please help me understand the Wiki’s 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 ...
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5answers
1k 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 ...
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1answer
98 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 ...
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1answer
112 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 ...
3
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1answer
153 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 ...
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0answers
171 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 ...

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