Questions tagged [kinetics]

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

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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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Equilibrium and Rates of Reaction

Consider the following equilibrium system: $\ce{A<=>2B}$ Suppose you were to establish equilibrium starting with 1mol of A (system 1), as opposed to starting with 2mol of B (system 2). I know ...
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Why does electronegativity, a parameter defined using thermodynamic properties. measure a kinetic property?

Electronegativity is said to be tendency for an atom to attract electrons, hence we can think of it as related to kinetic properties. However the definition of electronegativity is given as: $$ | \...
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Activation Energy and Equilibrium Position [closed]

Is the reaction direction with the lower activation energy favoured at equilibrium?
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kinetic energy of ejected electrons [closed]

Barium has a work function of Φ =2.520 eV. If 350.0 nm light is directed at the metal, what is the kinetic energy of the ejected electrons?
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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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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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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 ...
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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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60 views

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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907 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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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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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 ...
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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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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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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}]}...
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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-...
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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 ...
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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 mol1−(m+n)·L(m+n)−1·s−1 However, by the Arrhenius equation, k can be expressed as k = PZexp(-Ea/RT) and ...
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1answer
276 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 :$$ΔH= E_{\mathrm{activation,forward}}-E_{\mathrm{activation,backward}} \tag{1}$$ But I suspect that $ E_{\mathrm{activation,forward}...
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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 ...
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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. ...
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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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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{(...
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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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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 ...
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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 ...
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1answer
53 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 ...
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119 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 ...
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55 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)}\...
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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 ...
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Factors affecting rate of β-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 ...
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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 ...
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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: $$...
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Catalysts and activation energy

Do catalysts increase rate of reaction only by decreasing activation energy? Or can they affect the Arrhenius factor or reaction orders? Like if one catalyst is more effective at increasing rate of ...
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Equilibrium constant for heterogeneous equilibria having aqueous as well as gaseous reactants

Suppose we have a heterogenous equilibrium : $$\ce{A(aq) +B(aq) <=> C(g) +D(aq)}$$ Which equilibrium constant is used here? Both pressure and concentration terms are there. So, according to me, ...
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Finding the ratio of rate constants [closed]

A group of mountain climbers set up a camp at a $\pu{3 km}$ altitude and experience a barometric pressure of $\pu{0.69 atm}$. They discover that pure water boils at $\pu{90 ^\circ C}$ and that it ...
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Finding time t in a first order reaction (JEE Adv 2019) [closed]

The decomposition reaction $\ce{2N2O5(g) ->[\Delta] 2N2O4(g) + O2(g)}$ is started in a closed cylinder under isothermal conditions at an initial pressure of $\pu{1 atm}$. After $\pu{Y \times 10^{3} ...
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Electrolysis of aqueous solutions

Water competes with any ions in solution for both oxidation and reduction. There are $1000\ \mathrm{g\ l^{-1}}/18\ \mathrm{g\ mol^{-1}}\approx55.56\ \mathrm{mol\ l^{-1}}$. That is truly huge in ...
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Half life of first order reaction in case of variable volume [closed]

I have a doubt about the meaning of half-life of a first-order reaction. Earlier I used to think that it is the time in which concentration of reactant reduces to half of its initial but recently I ...
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How can I analytically calculate the rate of thermal decomposition of calcium carbonate?

I am a first-time poster on Chemistry StackExchange, and not much of a chemist. I'm trying to determine the rate of thermal decomposition (in mol/s) of calcium carbonate ($\ce{CaCO3}$) at various ...
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Kinetics of Sabatier reaction

I am modelling a methanation process in MATLAB, where I have a rate equation for methanation $$\ce{CO2 + 4 H2 → CH4 + 2 H2O}$$ in which I need partial pressure of $\ce{CO2},$ $\ce{H2},$ $\ce{CH4},$ $\...
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How are half lifes calculated for radioactive substances that decay over many years [duplicate]

How are the half lives (or whole lives) calculated for slowly decaying radioactive substances such as tellurium? I must be having a fundamental misunderstanding of how we are able to predict the ...
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1answer
56 views

Finding the sensitivity of zero-order ultra sensitivity and its parameter dependence

I am provided a one-dimensional reaction system showing zero-order ultra sensitivity. $$\ce{X_1 ->[f_1] X_2}, \quad \quad \quad \ce{X_2 ->[f_2] X_1}$$ The reaction rate function is the reduced ...
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The interactions of the high energy gas particles

When we are talking about the idealization of the gas, why for high temperatures its particles interact less? I would say you have a bigger probability of the collisions among particles. Quantum ...
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1answer
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Why do isotopes have different chemical reaction rates? [duplicate]

Isotopes of a given element differ in the rates at which they undergo chemical reaction. Why is this so? The only explanation I could think of is that the gravitational force on the electrons ...
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Do tert-butylcyclohexanes with a leaving group locked in the equatorial position undergo E1?

Background Elimination of 1-bromo-tert-butylcyclohexane is a prototypical example of how important the anti periplanar relationship is for E2. From Organic Chemistry: Structure, Mechanism, Synthesis ...
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Chain transfer agents and rate of free radical polymerization

In free radical addition polymerizations sometimes chain transfer agents are added. From what I understand chain transfer agents (e.g. XR' below) reduce the average molecular weight by transferring ...
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134 views

Half-life and shelf-life of second-order reaction

For integrated rate laws, I have attempted to find the shelf-life and half-life of second-order reaction: However, the answers I have obtained (which are labelled with a red cross) are very different ...
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178 views

Why does a first order reaction only depend on the concentration of a single reactant?

I am new to kinetics so please explain it from basic, If there is a reaction - $$\ce{A + B + C -> D}$$ In first order reaction rate is given by- $\mathrm R = k[\mathrm A]$ or $\mathrm R = k[\...

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