Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
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Why the Stoichiometric Coefficients are raised to the power of the concentration of the respective reactant? [duplicate]
While studying Chemical Kinetics, a question popped up in my mind that in Law of Mass Action, why the Stoichiometric Coefficients are raised to the power of the concentration of the respective ...
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If a reaction is not an elementary reaction, then will it be complex reaction? [closed]
Example- zero order reaction is not elementary, then will it become complex?
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How can zero order reactions be a multi step reaction?
I have heard that zero order reactions are always multi step reactions but what if the zero order reaction has only one reactant?
My textbook says that the number of molecules of a particular reactant ...
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First order kinetics
Finding time t in a first order reaction (JEE Adv 2019)
In reference to the above question,taking into account the stoichiometric coefficient, the standard equation of first order reaction time ...
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Specific temperature ranges of kinetic combustion mechanisms
Do kinetic combustion mechanisms typically operate within specific temperature ranges? I tested some mechanisms from the scientific literature, and apparently they were only working at temperatures ...
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Thermoplastics crystallization during nonisothermal cooling cycles
I have tested a PAEK family polymer using differential scanning calorimetry (DSC) with heating-cooling-heating cycles under different cooling rates (heating rates remained unchanged). PAEK are semi-...
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Half life of first order reaction maths
In first order reaction , t 99.9% ( time taken for 99.9% completion of reaction ) comes out as 10 x half life time. So you can either say that a reactant [A] ( A -> product , elementary reaction ) ...
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Units of Activation Energy
Consider the reaction
$$\ce{aA + bB -> cC + dD}$$ whose reactants are given by A and B and the products are C and D.
Say the activation energy of this reaction is some $x$ joules/mole, But moles of ...
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Why Michaelis Menten Assumption of equilibrium is necessary to integrate rate of ES production
I read in my textbook that the assumptions of equilibrium and of steady state used by Michaelis and Menten were simplifying assumptions intended to make the following equation one that can be ...
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Why is concentration never zero for zero order reactions? [closed]
By formula of zero order reaction:-
$$C_t=C_o-kt$$
The concentration should be zero at $t=C_0/k$. But in some books and websites I saw that graph between concentration and time don't touch the X-axis. ...
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Calculating Fractional Yield as a function of temperature for a parallel reaction in a plug flow model
(This question comes from a Chemical Engineering background, I hope it still falls in the scope of engineering.stackexchange.com If not, please move.)
I am trying to calculate and plot fractional ...
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why does rate determining step lead to these inequality relations?
Here, the rate expression for the mechanism (i) is below:
$$rate = \frac{K_1^2k_2k_3[H^+][A]^2}{k_{-2}+K_1k_3[A]}$$
and for (ii),
$$rate = \frac{K_1k_2k_3[H^+][A]^2}{k_{-2}[H^+]+k_3[A]}$$
I was asked ...
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What exactly are the stages of the reaction between an oxygen ion and a water molecule?
I found information on the website water.lsbu.ac.uk - Oxygen and water:
Between altitudes of $80-\pu{100 km}$, $\ce{O2^{\small{\bullet}+}}$ and $\ce{NO+}$ ions are the dominant cationic species. $\ce{...
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Explain estimating intercellular fluxes
Formula that I am using to calculate intercellular fluxes:
$$ J = \frac{4D}{\pi d} \big([C]_1 - [C]_2\big), $$
where the flux through a hole is $d$ of a solute with a diffusion coefficient $D$ that is ...
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Equilibrium constant of the formation of ferric thiocyanate
I was reading the paper Relaxation Kinetics of Ferric Thiocyanate (Goodall et. al, 1972) and I came across a passage which read
$\space$ Reaction (1) is the simplest representation of the equilibrium ...
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Derivation of the Van 't Hoff equation
I was reading the paper Relaxation Kinetics of Ferric Thiocyanate (Goodall et. al, 1972) and I came across the passage
Reaction (1) is the simplest representation of the equilibrium between ferric ...
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Is preferential oxidation/reduction at electrodes only dependent on the reduction potential or is it also dependent on kinetics?
It is commonly taught that in electrochemical cells where there are 2 different chemical species that can be oxidised/reduced, species with more positive actual reduction potentials (concentration ...
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Alleged temperature dependance of activation energy?
According to Master Organic Chemistry (https://www.masterorganicchemistry.com/2012/09/10/elimination-reactions-are-favored-by-heat/), in point number four, the activation energy for a reaction is ...
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Can Spectator Ions Affect Reaction Kinetics?
Specifically, I am interested in the reaction of different hydroxides (in aqueous form) with $\ce{CO_2}$. I would like to determine which hydroxide would conduct the reaction the fastest. My initial ...
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Effect of presence of competitive inhibitor on observed reaction constant
Suppose there is a solution of enzyme, its substrate, a competitive inhibitor, and a suicide inhibitor. The reaction rate constant for the reaction of the suicide inhibitor with the enzyme is known. ...
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Concentration units for kinetic mechanism of combustion
I am reading Tamás Turányi & Alison S. Tomlin's Analysis of Kinetic Reaction Mechanisms (2015). On page 10-11, the authors state that for a mechanism with $N_R$ reactions involving $N_S$ species, ...
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What is the reaction between crystal violet and bleach (sodium hypochlorite) and what is the mechanism of its action against crystal violet?
I'm trying to find the reaction between bleach (sodium hypochlorite) and crystal violet, and need to find the mechanism of its action, as during my lab investigation the bleach did cause the crystal ...
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Does stoichiometry matter in extent of reaction calculation?
I was recently introduced to the extent of reaction and learned that it can be calculated using this equation
$$\xi = \frac{n_{A,out}-n_{A,in}}{\nu_A}.$$
If I'm using this formula to calculate the ...
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Gibbs free energy of transition and activation energy
Let's consider a reaction A (reactant) -> B(product) and activated complex is denoted by C.
This graph ( potential energy vs reaction coordinate ) tells us that reactant need some amount of ...
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Is half-life defined for a reaction or for a reactant?
Consider the following chemical reaction.
$$\ce{A + B -> Products}$$
If this is a zero-order reaction with respect to $\ce{A}$ and $\ce{B}$, then is there a half-time for this reaction? Or must we ...
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Effect of competitive inhibitor on substrate inhibition
In an enzyme that undergoes substrate inhibition, how would the presence of a competitive inhibitor affect said substrate inhibition? Would the substrate concentration at which substrate inhibition ...
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Does someone know a unique testable questions surrounding 1 of the 5 variables that affect the rate of a chemical reaction? [closed]
I am a year 11 student studying high school chemistry and we are currently studying catalysts.
I am working on an assessment and need to come up with a unique but testable hypothesis surrounding one ...
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Why do we consider one elementary reaction to be in equilibrium while calculating rate law for complex reactions?
When we calculate rate of reaction pfor a complex reaction, if the rate determining step have intermediates, we calculate the rate of reaction using the step which is at equilibrium (and doesn't have ...
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How are enzyme inhibition constants assayed for "multi-inhibitors"?
Suppose there is a suicide inhibitor of an enzyme that reacts with the enzyme to form an inactive enzyme and another product. This "Another product", however, is capable of acting as a ...
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Non-elementary reactions: Relationship between kinetic and equilibrium constant
As far as I understand, the equation for a kinetic equilibrium is always the same, and is given by:
$$K = \frac{\text{concentration of products}^{p}} {\text{concentration of reactants}^{r}}$$
Where $p$...
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Is it a convention to divide rate of reaction by stoichiometric coefficient?
If we consider a reaction
$$ \ce{A + B -> 3 C} $$
The rate of reaction is given by
$$ R= -\dfrac{\Delta[A]}{\Delta t} = -\dfrac{\Delta[B]}{\Delta t} = \frac13\dfrac{\Delta[C]}{\Delta t} $$
I know ...
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How does the concentration of a reactant change? Is it based on individual order or overall order?
Reaction $\ce{A + B ->[$k$] C + D}$ follows the rate law $$r = k [\ce{A}]^{1/2}[\ce{B}]^{1/2}$$ where $k$ is given. Starting with $1 \,\pu{M}$ of $\ce{A}$ and $\ce{B}$ each, what is the time taken ...
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Why can we use stoichiometric coefficients in the equilibrium-constant expression? [duplicate]
I just studied the chapter on chemical kinetics on Coursera, wherein I was repeatedly admonished not to use the stoichiometric coefficients in the rate law formula. I was told that this formula has to ...
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Why decomposition of gas on metal surface at high pressure considered 0 order
While reading my textbook it says that when ammonia decompose on a platinum surface at high pressure, the reaction is 0 order because at high pressure the metal surface get saturated with ammonia ...
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Lifetime components in phosphorescence decay
I'm studying the phosphorescence decay of diacetyl in acetonitrile (it has a high quantum yield of intersystem crossing). The fluorimeter than I'm employing has microsecond resolution and, since the ...
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Non-Arrhenius temperature dependence of bimolecular reaction rates at very high temperatures
Once I have read that in some cases bimolecular reactions can exhibit a maximum as a function of temperature due to the short lifetime of the activated complex at very high temperatures.
At low ...
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What is the physical significance of the frequency factor in the Arrhenius equation?
As the title says, I am wondering what the physical significance of the frequency/pre-exponential factor in the Arrhenius equation. My idea of it is that:
If the units of $E_a$ are energy per molecule,...
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Sequential first order reaction graph in chemical kinetics
In graph given below is a sequential first order reaction
$$\ce{A ->[$k_1$] B ->[$k_2$] C}$$
For $k_2 \gg k_1$ the graph of concentration of $\ce{A}$, $\ce{B}$ and $\ce{C}$ is as follows.
Won't ...
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Is it possible for a reaction to change its order mid-reaction?
I encountered a problem which stated that the order of the reaction remained zero, until the concentration was halved. Then it became first order. Already, zero ordered reactions don't actually exist (...
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The isotopic effect in chemical kinetics
I conducted a chemical experiment (degree in chemical engineering) to understand the isotopic effect in chemical kinetics. In the experiment, I reacted isopropanol and D-isopropanol (D stands for ...
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What if kc=1 will reactants concentration equals to product concentration [closed]
I read a book, it says if kc=1 it mean reactant concentration equals to product concentration at equilibrium. But I'm wondering that in kc expression we dont just use concentration of an element we ...
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In a reversible reaction, how can endothermic and exothermic processes happen simultaneously?
A reversible reaction has both the forward and the backward reaction occurring at the same time. I struggle to understand how this is logically possible. One reaction pathway is always endothermic, ...
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Change of equilibrium constant with respect to temperature
Suppose we have an arbitrary chemical reaction $A+B\rightleftharpoons 2C+D$ and its equilibrium constant at two temperatures $T_{1},T_{2}$ are $k_{1},k_{2}$. We can relate them as
$$\log\frac{k_{2}}{...
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Approximate calculations of the product distribution under kinetic control
What is the product distribution when the energy difference between the transition states (∆TS = TS1 – TS2), is at 2 kcal/mol and when it is at 5 kcal/mol (assuming room temperature)?
I know that 1.4 ...
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Why are the derivatives of the concentrations divided by stoichiometric coefficients?
Consider this simple dioxygen to ozone chemical equation
$$\ce{3 O2 -> 2 O3}$$
with the average rate of the reaction
$$r = -\frac{1}{3}\frac{\Delta[\ce{O2}]}{\Delta t} = \frac{1}{2}\frac{\Delta[\ce{...
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Mass action law and conservation of mass [closed]
I am starting to learn about the use of mass action law in chemistry. I am doing some exercises to practice. In particular, I am considering the reaction
$$2 X \underset{3}{\stackrel{4}{\...
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Enamine formation mechanism. Can't there be alternatives?
I'm studying organic chemistry, more specifically the imines and enamines. I've read about the mechanism of formation of enamine from a generic ketone and a question popped up in my mind. The ...
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What are the differences between the different Rate Equations?
I currently am about to finish general chem 2 so my knowledge is still basic.
There are different kinetics and rate equations and im not quite sure I know the differences.
Breaking rate of a reactant:...
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How do metal hydrides behave in a non-hydrogen closed system?
I am curious about the fundamentals of metal hydrides and how adsorption/desorption works in non-hydrogen systems. My understanding is that the atom ratio M/Hx of the metal hydride is a function of ...
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Are there exceptions to the rate law for elementary reactions?
According to several authentic sources (for example, ChemLibreTexts), for elementary reactions, the order is equal to molecularity according to the rate law.
Example: For an elementary reaction $$\ce{...
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