Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
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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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How can a Michaelis–Menten formalism be used when enzyme concentration isn't constant?
I understand that $V_\mathrm{max} = k_3[\ce{E}]_0$ in ordinary Michaelis–Menten (MM) kinetics. According to the lecture notes provided by my university (I don't believe they are available online), ...
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Understanding elementary rate laws from a probability stand point
I am learning about chemical kinetics and dynamics and as I understand for a general chemical reaction
$$\ce{aA + bB -> cC + dD} $$ whose reaction rate, r, can be described by an elementary rate ...
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Is any significant product formed in the gas phase when reactants' concentrations are in the hundreds of ppm?
Title says it all. I am evaluating the chance that the IR signal of a mixture of gases changes due to their reaction with each other. Keep in mind that they are in the 3-3000 ppm range and include a ...
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order of the reaction with respect to acid ions
The acid catalysed hydrolysis of an organic compound $( \text{A} )$ at $( 303 \text{K} $) has a time for half change of $( 100\ \text{minutes} )$ when carried out in a buffer solution at $( \text{pH}...
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Finding the reaction order from a given plot of chemical kinetics
What will be the order of the reaction for a chemical change having $\log t_{1/2}$ VS $\log a$ Where $a=$ Initial concentration of reactant and $t_{1/2} =$ Half Life?
0 order
1st order
2nd order
None ...
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Steady-state approximation for thermal cracking
I was shown an application of the steady-state approximation to a thermal cracking reaction, which I think is not correct. The reaction is the thermal cracking of ethane: $\ce {C_2H_6 \rightarrow ...
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Parabolic Arrhenius plot
I am currently doing a kinetic study on an enzyme catalysed reaction and plotting the Arrhenius graph ($\ln k$ vs $1/T$) I got a parabola. My idea is to take the derivative at each point, meaning ...
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Frequency to induce nitrogen inversion
I would like to know how to compute the frequency at which nitrogen inversion happens in ammonia gas at STP. The activation energy for such process is 24.2 kJ/mol, therefore I thought that it is ...
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Testing Combustion Kinetic Mechanisms
The chemical modeling of combustion depends on kinetic mechanisms, that is, intricate networks of chemical reactions that describe the transformation of reactants into products. For a mechanism of $...
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Rate of Reaction - is it for convenience?
I am a high schooler, i had this doubt while studying chemical kinetics, consider this reaction(elementary) 2A --> B, now let rate of disapperance of A be 4 mol/Ls so now logically since change in ...
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Prove that concentrations of all species increase ultimately in a chemical equilibrium when pressure is increased
The statement:
For a chemical equilibrium in a sealed container, the concentration of "all" species always increases when the pressure of the mixture is increased by decreasing the volume of ...
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Multiple rate-determining steps and rate expression
I am trying to understand the concept of the rate laws governing hydrogen evolution of platinum. More specifically, I am trying to understand the multiple occurrence of a rds to the overall rate law ...
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Replacement for Centrifuge in Calcium Content Determination
Basically, I'm performing a lab investigation to determine calcium content in different milk sorts. Since my school didn't have any EDTA, I'm using Sodium Oxalate to form a precipitate with Calcium ...
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Identifying the rate-determining step from an energy-reaction coordinate diagram
I was wondering how a rate-determining step would be identified for an energy-reaction coordinate diagram. The RDS would be the step with the highest activiation energy, but relative to what? Relative ...
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Calculation of the specific rate constant (k)
Suppose we found that the reaction of Red#3 with bleach is 1st order in hypochlorite. The observed rate constant ($k_\mathrm{obs}$) for one of the trials was measured to be $\pu{0.00400 s^{-1}}$. If ...
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Correct Interpretation of Apparent Charge Transfer Coefficients
Good day guys,
I was looking over some $i$ vs $\eta $ for a redox reaction. The main reaction taking place is:
$$\ce{N2 + 6 Li+ + 6 e- -> 2 Li3N}$$
Plotting the data and fitting the Tafel equation ...
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Why would large activation energies give a large gradient of the rate constant?
I have read carefully this answer on SE, and there is a part I don't understand. SE exchange user said:
If you plot the Arrhenius equation (given in your text) vs temperature the slope of this gives ...
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Correct interpretation of Impedance: IR-Drop and Nyquist plots
Good day guys,
I have been lately studying impedance and IR drop in electrochemical systems.
From my readings I have come across different interpretations.
According to my books, from the Nyquist plot:...
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Limiting current vs Steady-state limiting current
I have been reading on the concept of limiting current.
In books, the mass-transfer limiting current is given by,
$$ i_L = \frac{nFADC^*}{\delta}$$
Often the Cottrell equation is introduced.
However, ...
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Why isn't the rate of an elementary reaction expressed in activity?
Why don't chemists use $r_\ce{X}=\frac{\text{d}a_\ce{X}}{\text{d}t}$ where $a_\ce{X}$ is the chemical activity of species $\ce{X}$ and corresponding rate law for elementary reactions as $r=ka_1^{\...
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Differentiating random and ordered sequential mechanisms in enzyme kinetics
Can random and ordered sequential mechanisms be descern by Lineweaver-Burk plot? Why or why not? Because for orederd sequential mechanism I got different LB plot depending on which substrate is held ...
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Why reaction rate has to be necessarily positive?
I read in my book that negative rates do not have any significance.
Can't we interpret negative rate simply as decrease in concentration of reactant?
What's wrong with that and why do we put an ...
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when to use exponents, or multiply by constants in the equation of the rate involving $k$ and concentrations?
More specifically, I do not understand
rate of consuming $\ce{I}=2 k_2[\mathrm{I}]^2+2 k_3\left[\mathrm{H}_2\right][\mathrm{I}]^2$
Why is the concentration of $"\ce{I}"$ squared from $"2 \cdot k_3 \...
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How are major products defined- Thermodynamically or Kinetically?
In many organic chemistry questions, we use mechanisms that favours thermodynamically stable product (like aromatic rings), compromising the rate by some factor. For example, if there were two ...
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What is the particle speed in liquids at an average room temperature (20-25 degrees celcius)?
I've been searching online for ages and I can't find anything related to this, everything seems to be about gas particles relating to temperature. I'm investigating simple chemistry related to ...
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Convection or Advection term in the Absolute flux of a chemical species
I am confused as I have been reading on mass transport on multiple sources and they seem to use "advection" and "convection" interchangeably in the equation for the absolute flux ...
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Iminium formation rate between formaldehyde and secondary amine
Given the significantly more favored hydrate of formaldehyde in the presence of water under neutral conditions, can we say that this is the slow step in iminium formation? Would removing water/working ...
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Does increasing temperature increase the rate of gaseous reactions?
In chemical kinetics there is a generalised statement that the rate of reaction is dependent upon
the concentration of reactants (except for zero order/complex reactions)
temperature
catalyst
surface ...
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Briggs-Rauscher Reaction potential
I have seen many graphs on the oscillation reaction of the Briggs-Rauscher reaction. They all have potential in V or mV in the y-axis. My question is what this tells about the rate of reaction of the ...
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Is there a difference between equilibrium and steady state?
The term equilibrium is used in the context of reversible reactions that reach a point where concentrations no longer change. The term steady-state is used in enzyme kinetics when the concentration of ...
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How long must a sample last in a molecular dynamics run for it to be considered non-labile?
So I have a few unusual molecules and I wanted to know whether or not they are kinetically stable (non-labile) across a certain range of temperatures. The methods for synthesizing these molecules isn'...
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Why is the decomposition of gas on a metal surface at high pressure considered a 0 order reaction?
My textbook says that when ammonia decomposes on a platinum surface at high pressure, the reaction is 0-order. This is because at high pressures, the metal surface gets saturated with ammonia ...
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Why does the rate law of Cannizzaro reaction include a term for base?
The rate law of Cannizzaro reaction in mild base is
$$\mathrm{rate_1} = k[\ce{RCHO}]^2 [\ce{OH^-}],\tag{1}$$
while in concentrated base the rate becomes
$$\mathrm{rate_2} = k[\ce{RCHO}]^2[\ce{OH^-}]^2\...
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pH at maximum concentration of a certain species (Phosphoric acid) [closed]
I am trying to find the pH at which $[H_{2}PO_{4} ^{-}]$ is maximum by only knowing the pKas.
I have tried to derive an equation using kinetics but it failed [1].
After taking a look at the Sillén/...
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Can increasing concentration of reactants make the RDS no longer the slowest step in the mechanism?
The rate determining step is said to determine the overall rate of reaction because it is the slowest step in the mechanism. However, increasing the concentrations of reactants in this step can ...
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How does an oscillating reaction work?
I watched a Belousov--Zhabotinsky reaction video showing an orange solution that goes to clear and then back to orange (and so forth.)
The reaction goes through a number of cycles before it will no ...
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Why does iodate and acidified metabisulfite solution turn yellow instead of blue at high temperatures (above 50)
We are doing a kinetics investigation at school where we are trying to find the activation energy of the reaction between potassium iodate and sodium metabisulfite. Solution A contains 2g of potassium ...
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Should I round an experimentally determined reaction order to an integer?
For a lab experiment I did, I calculated the reaction order for one of the reactants using data from two trials, both rates, and the concentration of that reactant during each.
$$
\frac{\text{Rate}_1}{...
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Could an airborne swarm of small insects explode? [closed]
I know that fine-grained organic matter such as flour or pollen can be quite explosive if ignited. It also seems logical to me that the explosiveness of such an organic powder is determined by many ...
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Reactivity of Grignard reagent
I had the following question at an exam:
What is the fastest reacting compound towards nucleophilic addition with Grignard reagent?
(a) Acyl chloride
(b) Aldehyde
(c) Ester
It is obvious that ester ...
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Which is faster- SN1 or SN2?
We were studying about nucleophilic substitution reactions. My professor said that in general SN1 reactions are faster than SN2 reactions. I am unable to understand that how can we generalise the rate ...
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Why are rates of reaction faster for ionic compounds than for covalent compounds?
Why is it that ionic reactions (i.e., reactions involving ionic compounds) are faster than covalent reactions (reactions involving covalent compounds), even though the ionic bond is stronger than the ...
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Is it possible to calculate the theoretical rate of reaction?
I am conducting an experiment where I will be changing concentration (0.2 mol/dm3, 0.4 mol/dm3, 0.6 mol/dm3, 0.8 mol/dm3, 1.0 mol/dm3) and seeing how that affects the rate of reaction for a reaction ...
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How is it even possible that vapour pressure of liquid and vapour of solid are equal at freezing point? [duplicate]
My text book states The freezing point is defined as "the temperature at which the vapor pressure of the substance in its liquid phase is equal to its vapor pressure in the solid phase" Also ...
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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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Define a rate-determining step and an energy barrier for a multi-step reaction profile
I am currently making reaction profile by means of DFT calculations. I am able to correctly draw a whole reaction profile.
However, I am struggling to find what exactly is the energy barrier of a ...
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Why is reaction rate proportional to the order of reactants? [duplicate]
I know that for some elementary reaction $m\text{A}+n\text{B}\rightarrow\text{C}$, the rate of reaction is given by $-\frac{\text{dA}}{\text{dt}}=k[\text{A}]^m[\text{B}]^n$.
Now if we consider the ...
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Reason for differences in AChE aging/reactivation kinetics between neutral and charged organophosphorus inhibitors
According to the referenced papers, acetylcholinesterase that has been inhibited by an organophosphate possessing thiocholine as its leaving group is more susceptible to reactivation by oxime ...
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Why doesn't HBr show allylic substitution in presence of Peroxide?
HBr reacts with alkenes such as propene in the presence of Peroxide as per the Anti-Markovnikov rule. This is an addition reaction, forming 1-bromopropane as the major product.
This happens due to the ...
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