Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
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Finding the average rate of consumption
The question is:
If $2.0 \cdot 10^{-4}$ moles of dye in $\pu{50 mL}$ of solution is consumed in 188 seconds, what is the average rate of consumption of dye in $\pu{mol L-1 s-1}$?
I am not sure if I ...
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Evaporation velocity of ethanol: adding ethanol vapour to a gas mixture
I need to add a known amount of ethanol vapour to a gas mixture (He/Ar). To do that I let the mixture bubble in liquid ethanol kept at a known temperature (14 C).
The system is made of a large steel ...
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Determining order of a reaction without isolation
I'm writing a computer program to calculate the order of a chemical reaction with respect to each reactant. When I do this by hand, it's easy to isolate which reactant concentration stays relatively ...
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Which of the these SN1 solvolysis of two alkenyl bromides reactions is faster?
The SN1 solvolysis of one of the following alkenyl bromides is in MeOH approximately 100000 times faster than the other one. Which is the more reactive one? Draw the mechanism including the transition ...
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How do I calculate the order of a reaction given slope?
I'm an AP Chemistry student, and we're doing the Decomposition of $\ce{H2O2}$ lab, in which we decompose $\ce{H2O2}$ with $\ce{KI}$ as a catalyst. I've gotten this data so far:
...
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How to calculate the frequency of cyclohexane conformational interconversion?
My book mentioned that the energy barrier for cyclohexane to reach the half-chair conformation is $50.6\ \mathrm{kJ\ mol^{-1}}$. It says that from this value, it was calculated that cyclohexane ...
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How can molecularity be the order of the rate determining step?
In my textbook the molecularity is defined as(along with the standard definition) the order of the rate determining step(RDS). It is also given that the order can be a fraction but molecularity is ...
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What is the scaling for % completion time in a Michaelis–Menten scenario as a function of substrate concentration?
Say I have a straightforward Michaelis-Menten reaction where an enzyme $E$ at some fixed concentration $[E]$ forms an interaction complex $ES$ with a substrate $S$ (with initial concentration $[S]_0$),...
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How to estimate reaction products of competitive binding?
I have two reactions,
$$\ce{A + C \rightleftharpoons AC}$$
$$\ce{B + C \rightleftharpoons BC}$$
I'd like to estimate the relative steady state proportions
$$\frac{[\ce{BC}]_{SS}}{[\ce{AC}]_{SS}+[\...
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Rate of electrophilic bromination of toluene and ethylbenzene
My book says that electrophilic bromination of toluene (methylbenzene) is faster than that of ethylbenzene. How is that possible?
I am doubting it because ethyl is a better $+\ce{I}$ group than ...
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Is there a general consensus on the causes of the alpha-effect?
There have been various explanations posited for the α-effect. The α-effect refers to a phenomenon wherein nucleophiles with lone pairs on atoms adjacent (i.e., in the α- position) to the atom bearing ...
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Speed of ionic reactions?
Why are ionic reactions extremely fast, as compared to other gaseous
reactions?
The ionic reactions (precipitations, neutralizations etc.) are extremely fast (somewhere about $10^{12}$ times ...
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How does the inductive effect, explain the reactivity of tertiary alcohols with halogen acids?
The reactions of primary and secondary alcohols with halogen acids ($\ce{HX}$, where $\ce{X}$=halogen) require the presence of a catalyst, $\ce{ZnCl_2}$. With tertiary alcohols, the reaction is ...
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How exactly is activation energy defined?
In a common interpretation of the Arrhenius rate equation
$$k = A\exp\left(-\frac{E_\mathrm a}{RT}\right),$$
the activation energy $E_\mathrm a$ is understood to represent the difference in the ...
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How to find the units of the rate constant?
Consider the reaction $$\ce{2A + B -> Products},$$ when the concentration of $\ce{B}$ alone was doubled, the half-life did not change. When the concentration of $\ce{A}$ alone was doubled, the rate ...
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How can I go about obtaining the activation enthalpy of a reaction using the Arrhenius Equation experimentally?
I plan to do a string of experiments on the kinetics of the decomposition of hydrogen peroxide. I’m going to see the effect of catalyst concentration on rate and the effect of varying hydrogen ...
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How is it that the equilibrium constant does not depend on the mechanism?
For a reaction of the form
$$\ce{aA + bB <=> cC + dD}$$
the equilibrium constant is
$$K_c=\frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{A}]^a[\ce{B}]^b}$$
regardless of the mechanism of the reaction. ...
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Does the hydrolysis speed increase when more H+ ions are in the solution?
In hydrolysis of polysaccharides, does the hydrolysis speed increase when more $\ce{H+}$ ions are present in the solution?
So if I were to use $\ce{H2SO4}$ instead of $\ce{HCl}$ (same volumes) then $\...
user2117
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How does initial rate of reaction imply rate of reaction at any time?
My textbook begins the Chemical Kinetics section by describing the "Initial Rates Method" of determining the rate of reaction. I understood it as the following (for a first order reaction):
$$\ce{A -&...
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Storing kinetic energy in bonds
Let's assume a setup with a static linear molecule with three identical atoms connected by bonds and a single atom, identical to the other three, being shot at the molecule. Let's also assume that ...
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Analytical solution to first-order rate laws
Does anyone know the analytical solutions to the following rate laws:
1) $\frac{\mathrm{d}\rho_\text{W}}{\mathrm{d}t} = -\rho_\text{W} \cdot (K_1+K_2+K_3)$
2) $\frac{\mathrm{d}\rho_\text{T}}{\mathrm{...
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Difference between Reaction Rate and Rate Law?
Lets say you have the reaction
$$\ce{$a$A + $b$B -> $c$C + $d$D}$$
The rate of the reaction is given by the change in initial concentration over the change in time.
$$-\frac{\Delta \left[\ce A \...
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How should I modify my molecular dynamics simulation so that known chemical reactions can be modelled?
I have written some molecular dynamics code that I want to use to model known chemical reactions.
By known I mean that it has been observed in a lab that $\ce{A +B->C}$.
I am not interested in ...
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What is the reaction order of a reaction?
Here's is what I understand so far and the following is referenced directly from UNSW CHEM1061 lecture notes by Professor Pall Thordarson:
order of the reaction SHOULD be equal to the number of ...
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What does an endpoint saturated signal mean. How does it relate to equilibrium constant?
I have had a question that has been bugging me for a couple of years in my graduate school career, and I was wondering if perhaps someone could help explain it to me. Given an endpoint assay like this ...
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Integrated rate law graphs
Why does the graph of $\ln[\ce A]$ vs $t$ produce a straight line for the first order rate law?
Also why does the graph of $t$ vs $\frac{1}{B}$ produce a straight line for the second order rate law?
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Estimating Surface Reactions - Liquid, Turbulent Flow
So, I need a method of estimating the influence of a surface (rate constant would do for a start), the idea is to estimate just Reactant + Surface -> Product in a turbulent liquid flow.
Now I am ...
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Michaelis Menten derivation for 2 enzyme substrates
We know the Michaelis Menten derivation for the following reaction:
$$\ce{E + S <=> ES -> E + P}$$
However, what if the reaction took place in a different scenario whereby:
$$\ce{E + S <...
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Where do the rate laws for the Chlorine Dioxide-Iodine-Malonic Acid reaction come from?
After reading a section on this particular oscillatory reaction, something started bugging me about it.
However, let me lay out the basis of my question. From what I've researched, Lengyel and ...
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Iodine clock with moving bands
Has anyone seen a version of the iodine clock reaction where instead of the system oscillating between clear and blue it shows blue bands travelling down the vessel?
I ask because someone not unknown ...
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Using Arrhenius equation to calculate the ratio of two reaction rates
For two reactions,
$$\begin{align}
\ce{A ->[$k_1$] B} \tag{1} \\
\ce{A ->[$k_2$] C} \tag{2}
\end{align}$$
you have determined that the activation energies are $\pu{71.9 kJ/mol}$ for $(...
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Difference between the terms "autocatalysis" and "(branching) chain reaction"
Is there a technical difference between the terms "autocatalysis" and "branching chain reaction"? They both seem to refer to something very similar, namely sequences of reactions in which one of the ...
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What are the factors controlling the fate of post-adhesed volatile molecules of the olfactory epithelium?
What happens to volatile molecules that reach the main olfactory epithelium in the nasal cavity after they bind and the neural stimulus fades?
To what extent do such factors as receptor kinetics and ...
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Integrated rate laws
My teacher gave us the equations for zero-order, first-order and second-order reactions as follows:
$$ [A]_t = -akt + [A]_0 $$
$$ \ln [A]_t=-akt+\ln [A]_0$$
$$\frac1{[A]_t}=akt+\frac1{[A]_0}$$
...
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What reactions will their reaction rates increase with time?
My textbook states that for most reactions, the reaction rate decreases with time. I wonder what reactions will have increasing reaction rates with time. I know that adding a catalyst will increase ...
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Is there a bifurcation node in the potential energy as a function of reaction progress equation of chemical reactions?
I originally posted a similar question on math.stackexchange.com, but I believe I might have a better chance of having my question answered here after giving it some time.
I was thinking about the ...
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Difference between thermodynamic and kinetic stability
What is the difference between thermodynamic and kinetic stability? I'd like a basic explanation, but not too simple. For example, methane does not burn until lit -- why?
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A first-order reaction at infinite concentration
I have a first-order reaction, for the binding of two molecules, of the form: $\text{k}_\text{f} = \ce{k_1 (M*s)^{-1}}$. What happens at infinite concentration? How is this upperbound typically ...
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Introduction to modeling chemical reactions
I am looking for introduction to modeling of chemical reactions. I think there is the base approach, where concentrations of chemical species are given, plus ratios of each possible reaction / outcome....
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Why are equilibrium constants unitless?
I haven’t quite reached the point where I can read a full-fledged text on chemical kinetics and thermodynamics yet, so bear with me, please.
I’m wondering why a value like $K_\text{eq} = \frac{[\ce{...
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Why do collisions in elementary reactions of higher-orders appear to be more likely?
So we are told that a unimolecular elementary reaction has a rate law of $k[\text{A}]$ where a termolecular reaction with three unique reagents, $A$, $B$ and $C$ has a rate law of $k[\text{A}][\text{B}...
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Very slow chemical clock reaction
I'd like to preface this with a declaration of my understanding that this is not necessarily possible.
I was wondering if anyone knew of a chemical clock reaction where the period before the first ...
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Algebra of conserved quantities for chemical reactions
So there is the standard formation enthalpy $\Delta H^0_f$ and there is also formation entropy.
Are there more (independent) quantities? What about the heat capacity? Is there a general theoretical ...
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Difference between non-thermal and thermal ionized gases
Why or when does non-thermal plasma become thermal? How do we know before hand if the ion temperature will differ from the electron temperature, on what parameters does it depend - where is the ...
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Why is a metabisulfite / starch / HCl solution unstable?
In one variation of the iodine clock demonstration, you add two colorless solutions together and apparently nothing happens. After about 30 seconds to a minute, you get an "instantaneous" change to a ...
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What is the probability of 3 possible products, between two chemical species?
I am not a chemist. I hope I will be specific enough.
Suppose there are two chemical species $\ce{A}$, $\ce{B}$ with the following properties:
at temperature $t < T_r$, no reaction occurs between ...
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Definitions of autocatalysis
Is there a formal definition or algorithm that can take a list of reactions and tell me whether it contains a set of species that can produce itself autocatalytically?
It is clear that the following ...
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What's a minimal yet chemically-meaningful kinetic system for an oscillating reaction?
Oscillating reactions are a funny aspect of chemistry. I have tried to find various simplified kinetic models of oscillating reactions such as the Belouzov-Zhabotinsky, the Briggs–Rauscher or the Bray–...
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How to identify zero order reactions?
I have come across many reactions that are zero order reactions but at one glance I'm unable to tell if they are zero order or not. Is there any criteria that can be used to identify these reactions ...
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Timescale of Protonation and Deprotonation across micelle layers
I am curious about the timescales of protonation and deprotonation of solvent systems. As a followup, how is this affected when the proton source is separated by an organic phase? For instance, it is ...
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