The study of rates and steps (mechanisms) of chemical processes.

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Calculating the rate of hydrolysis experimental

I am going to do a laboratory practical where we hydrolise halogenoalkane and determine the rate of reaction, this by adding silvernitrate that reacts with the formed halogenide and precipitates. My ...
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How to make sense of the 'Relaxation Method' for measuring reaction kinetics?

I get the concept that one can measure the rate of reaction by measuring the rate at which an equilibrium state reaches another equilibrium state after the system is perturbed (usually by heating). ...
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42 views

Question about Rate Reactions

Is there a name for the point where a First Order rate of reaction meets a Second Order one. This point highlighted above.
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35 views

How is the Rate Law of a reaction measured?

What is Rate Law of the reaction below?$$\ce{4 HBr + O2 -> 2 H2O + 2 Br2}$$ How do we approach finding the rate law of reaction? Can this be found out only through experiments?
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Why is the rate of disappearance negative?

Rate of disappearance is given as $-\frac{\Delta [A]}{\Delta t}$ where A is a reactant. However, using this formula, the rate of disappearance cannot be negative. $\Delta [A]$ will be negative, as ...
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Why is it not possible to determine the rate constant this way?

The following equation can be used to determine the rate: $Rate = \frac{-\Delta [A]}{\Delta t}$ This equation can also be used: $Rate = k[A]$ By simple substitution, $\frac{-\Delta [A]}{\Delta t} = ...
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In the elementary steps of a reaction, why do we assume that the coefficients of a reactant corresponds to its order?

Recently, I was taught that the coefficients of the reactants in an elementary step of a reaction indicates that reactant's order. Why is this the case? I thought that the order of a reactant was not ...
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152 views

Why is the units of kcat 1/s?

I understand that $k_\text{cat}$ measures the turnover number of an enzyme. This measure is therefore a quantity of molecule conversions per unit of time. I suspect that my problem is more that of a ...
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21 views

What are the possible concentration pathways for a 3-species system?

Inspired by this question, which asks if a multi-species system could oscillate around its equilibrium, I thought about the possible concentration pathways the following more narrow specified system ...
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95 views

How to solve an Arrhenius equation problem?

A widely used rule-of-thumb for the temperature dependence of a reaction rate is that a ten degree rise in the temperature approximately doubles the rate. This is not generally true, especially when a ...
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Does product induced poisoning qualify as a rate limiting step?

I have a question about whether a particular situation qualifies as a rate limiting step. I have a catalyst that under normal conditions gets poisoned when products accumulate on the catalyst surface. ...
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31 views

Stuck with derivation of the integrated rate equation for a pseudo first order equilibrium reaction

I was reading about the integrated rate law. However I have problems to follow the solution. I have an equilibrium reaction: [A]+[B]=[AB] with forward and back reaction. I approximate the ...
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41 views

Can there be more than one combination of reactant/product concentration for a specific equilibrium constant?

For an elementary reaction like $$\ce{A + B -> AB},$$ $$K_{c} = \frac{\ce{[AB]}}{\ce{[A][B]}}$$ and $$\frac{\mathrm{d}\ce{[AB]}}{\mathrm{d}t} = k\ce{[A][B]}.$$ If I let the reaction reach ...
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42 views

Why does radioactive decay occur?

Is there a reason radioactive decay is exponential, as in after an extremely long time some of the original compound remains, or is this just an empirical model? Also, why does $\ce{^{238}U}$ have a ...
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37 views

Iodine and persulfate kinetics: What can be deduced from graph?

From a graph of iodine concentration vs time of the reaction of iodide with persulfate, what can be deduced? Is it possible to find the order with respect to iodide and with respect to persulfate?
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Finding rate constant at different temperature

For the reaction $$ \ce{2N2O5(g) -> 4NO2 + O2(g)} $$ the rate law is: $$ \frac{\mathrm{d}[\ce{O2}]}{\mathrm{d}t} = k[\ce{N2O5}] $$ At 300 K, the half-life is 2.50·104 seconds and the activation ...
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What is the non-ideal equivalent of mass action kinetics?

Starting from the equations of mass action kinetics, one may show that (for suitably chosen numbers $A_i$), the function $\sum_i x_i(A_i + \log x_i)$ is a Lyapunov function, i.e. it decreases over ...
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Improving a mathematical model of a chemical reaction

I want to improve a mathematical model to suggest a rate expression. How can I do it by using relative absorbance values? The reaction is UV-catalyst decomposition. I don't know concentration values ...
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142 views

“There are no chemical cliffs”

Are there any reactions with no activation energies? Prof just told us there are no chemical cliffs. Is this true? I read something about nuclear decay as being a reaction with no activation ...
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102 views

Finding Root-Mean-Square of Ne using kinetic energy?

I am not being able to solve the following question: -Find the root-mean-square speed of $\ce{Ne}$ atoms at the temperature at which their kinetic energy is $\mathrm{6.24\ kJ/mol}$. I tried ...
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1answer
102 views

How can a catalyst not be included in a rate equation, if it by definition speeds up a chemical reaction?

I thought that anything not in a rate equation was automatically zeroth order and therefore did not affect the reaction? But I have heard that catalysts can be involved in a reaction while not being ...
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52 views

Radioactivity and Kinetics of disintegration

Well I've just started on kinetics and there are a few things I am absolutely confused about! First of all , is neutron actually made up of a proton and electron? if yes then how is it possible? In ...
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101 views

A few basic questions about activation energy and the Maxwell-Boltzmann distribution

I understand activation energy to be the relative difference in energy between that of the activated complex/transition state (at some temperature) and the average energy of the reactants like shown ...
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Oxidation of formate ion by peroxydisulfate in water solution: Why are there “strange” kinetics?

As you can see, the first step is the slowest, but by using the rate-determining step approximation you wouldn't arrive at the correct rate law which is: $r=k\ce{[HCOO^{−}]}^{1/2} ...
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Rate law and rate constant [closed]

How do we obtain the expressions for integrated rate laws ?!? What are the limits we integrate it under and with respect to what do we integrate it?
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Reversible elementary reaction

I have a question regarding a reversible elementary reaction: If we have an equilibrium where $$\ce{A<=>[k_1][k_{-1}]B}$$ , then $$-d[A]/dt= k_1[A]-k_{-1}[B]$$. If we take $$[B]=[B]_0 + ([A]_0 ...
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58 views

Significance of Kinetic Velocities?

In the concept of Kinetic Molecular Theory we have rms(root mean square), avg(average) and mp(most probable) velocities. I understand the concept well. But my question is why do we have three ...
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112 views

Molecularity vs Order Of Reaction

In the field of Chemical Kinetics, terms like Molecularity and Order Of Reactions are often used. I am a bit confused between these two terms. Can someone explain to me about these two terms and ...
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87 views

What is the constant of integration in a series reaction in chemical kinetics?

I have a question regarding the rates for a series reaction in kinetics. So imagine $\ce{A -> B -> C}$, with $k_1$ as rate constant for $\ce{A -> B}$ and $k_2$ as rate constant for $\ce{B ...
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587 views

Why is proton transfer so fast?

Why is proton transfer always kinetically favored? In other words, why are Bronsted acid-base reactions so quick? Is it because protons are generally unhindered, sterically? This seems plausible; ...
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84 views

Formation of 2,4-Dichlorophenol by free chlorine mediated oxidation of Triclosan

I cannot find much guidance in the literature. This is the reaction between free chlorine in water and triclosan. I understand ether cleavage and electrophilic aromatic substitution (maybe) involved. ...
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87 views

Rates of reaction

Assume a reaction is of second order kinetics and that the rate constant is k. The differential rate equation is given by: A+B->Products -dCa/dt = kCaCb Show that the general expression of ...
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Can in any case the faster step of the reaction be rate determining?

I found a sentence in book which states the reverse step of this reaction ( I forgot what was it!) has the faster step as rate determining . Even Rate determining step-Wikipedia states: In ...
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141 views

Determining exponents in a rate law with different data

Here is the experimental data: Note all concentrations are the initial amounts \begin{array}{cccc} \text{Experiment} & \ce{[C_{2}H_{4}Br_{2}]} &\ce{[I^{-}]} & \text{Initial rate of ...
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Show proposed mechanism is consistent with the experimental rate law

The mechanism for the reaction: \begin{align} \ce{NO_{(g)} + O_{2(g)} &<=>[k_{-1}][k_{1}] NO_{3(g)}} &\text{(fast)}\\ \ce{NO_{3(g)} + NO_{(g)} &<=>[K_{2}] 2\,NO_{2(g)}} ...
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581 views

Why are methanol flames less visible than other flames?

The combustion of methanol tends to generate flames that are less visible than the flames generated by the combustion of other substances? My guess is that methanol burns quickly as it has a ...
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38 views

Where can I find Equilibrium Constants?

When trying to develop mathematical models to show the concentration in a reaction, where can one find a database or good source of known equilibrium constants if it is not necessarily very convenient ...
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102 views

Can a multi-species system oscillate around equilibrium?

In reading about chemical oscillations such as those that occur in the Belousov–Zhabotinsky reaction (BZ), it's often reported that these reactions were initially not taken seriously, because of a ...
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126 views

Rate-determining step and steady state approximation failure

1) When can't the rate-determining step be applied, and why? How do you recognize these cases? 2) When can't the steady state approximation be applied, and why?
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161 views

What is the correct definition of the Gibbs free energy of activation?

Is the following correct? Gibbs free energy of activation is used in energy profiles where the stabilities of the species are expressed as changes in Gibbs energy, while the activation energy Ea ...
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Analytically combining Dynamic Equilibria that have a two way affect?

Lets say I want to model a water system as the following set of equilibria: $\ce{H2O <=> OH- + H3O+}$ | $\ce{A=[OH^{-}][H3O+]}$ $\ce{CO2 + H2O <=> H2CO3}$ | ...
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115 views

Why is the equilbrium constant expressed the way it is?

Why are the two molarity's multiplied and not added and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply ...
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136 views

Rate-limiting in transition state theory

Suppose an initial state $A$ can transition to either state $C$ or state $D$. Suppose further that both of these two processes are rate-limited by a transition to the same intermediate state $B$, as ...
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116 views

Relationship between rate equation and equilibrium constant

I have read mannaia's answer on the question of 'rate order and confusion', as well as Nicolau Saker Neto's answer to a related question. They have both been very helpful. As I understand, the ...
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157 views

Kinetic and Thermodynamic Stability

My prof noted that if the two components of any ionic compound undergo a large extent reaction with each other, then the substance CANNOT exist as a pure substance. For example, consider ammonium ...
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Formation Constants; Lewis Acidity

I still distinctly remember reading about how Lewis acidity/basicity was characterized using kinetics. The reason given was that because formation constants are so large, these reactions are not ...
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What are the units for m in the average kinetic energy formula?

For the equation $E_k=\frac{1}{2}mu^2$ what does the $m$ variable represent? I would say mass but the textbook does not say explicitly that it is anything.
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What is reactivity really, and can it be quantified?

I understand the concept of a reactive species on a sort of vague and intuitive level: a reactive species is one that has lots of reactions that it can participate in. These tend to have large kinetic ...
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Plot of Arrhenius Equation with temperature

I saw the plot of Arrhenius Equation Here It is a concave upwards graph, but acc to the equation $k= A e^\frac{-E_a}{RT},$ it is evident that the graph is of the form $y= e^\frac{-1}{x}.$ I ...
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Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

Take for instance the rection $$\ce{H2(g) + I2(s) -> 2HI(g)}$$ The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a constant, ...