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

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Chemical reactions as exponential functions

Are all graphs of molar concentration vs. time, for the reactants, exponential decay functions? (Until equilibrium is reached, if it goes equilibrium at all.) If so, intuitively, why is that the ...
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Solvation rates of crystalline and noncrystalline materials

Assuming equal surface area (and other variables), would a highly ordered crystal of some substance dissolve more slowly or quickly than (or at the same rate as) a disordered sample of the same ...
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Kinetic Isotopic Effect in EAS

It is observed that rate of reaction of two isotopologues of benzene, $\cf{C6D6}$ and $\cf{C6H6}$, is the same for electrophilic aromatic reactions, as the deprotonation is not the rate limiting step. ...
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What is first order reaction rate? [on hold]

Molecular iodine, $\ce{I2(g)}$, dissociates into iodine atoms at $625\ \mathrm{K}$ with a first-order rate constant of $0.271\ \mathrm{s^{-1}}$? What is the half-life for this reaction? (in s) ...
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Why is equilibrium constant unitless? [duplicate]

Why is equilibrium constant like kp and kc unitless? It should be unitless when the number of product and reactant molecules are equal but why is it so in other cases?
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Why is activation energy temperature independent?

I know that activation energy for a reaction is the extra energy given to the reactants to reach the threshold energy so that they can collide and react. But then, why is it said that the activation ...
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Importance of Overall Reaction Order

All my texts make it a point that in a differential rate law, the sum of the exponents on the reactant concentrations add up to the overall reaction order. However, I have yet to see any use in this. ...
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Does light intensity effect the rate of reaction of halogenation

So I need to complete a chemistry IB hl internal assessment, and I came up with this idea. I need to design a quantifiable lab in order to analyze a certain relationship. I'm not sure if this is a ...
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Kinetic Barrier of ATP

I do a fair bit of biochemistry, and one of the things I've taken on faith up until now is that ATP is stable because it has a high kinetic barrier for falling apart despite the spontaneity of its ...
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31 views

What is the relation between chemical thermodynamics and chemical kinetics? [closed]

Can one be understood on the basis of the other or are they not interrelated at all? The first thing my kinetics textbook demonstrated was how thermodynamics ignores time taken for a process whereas ...
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Factors that affect Diels-Alder reaction rate

As for factors that affect the rate of the Diels Alder reaction, having an s-cis conformation is primary. But in a case as shown below, what makes the second diene react faster compared to the third? ...
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Stability of CN molecule

The CN molecule has been observed spectroscopically in comets where pressure has been estimated to be as low as $10^{-10}$ mm Hg. Draw a Lewis structure for CN. Suggest an explanation as to why this ...
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35 views

Question regarding nitric acid, magnesium powder and initial reaction rate

For the question regarding the initial reaction rate, I don't quite understand why the answer is D. If I calculated the number of moles from the volume and conc, I would get A=0.4 moles; B=0.2 ...
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61 views

Zero order half life

On a homework problem the question is: Two substances A and B react with each other in such a way that A is 50% consumed in 33 minutes and 75% consumed in 66 minutes. Changing the concentration ...
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Enzyme-Kinetics. Michaelis-Menten Curve

A question regarding the Michaelis-Menten curve. For those of you who are well-versed in chemical kinetics(or even better, enzyme-kinetics) you most likely have come across this curve before. It is a ...
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1answer
61 views

SN1 vs SN2 in low concentration of nucleophile

Why is SN1 mechanism favoured by low concentration of nucleophilic reagent? It is a first order reaction so shouldn't the reagent be in excess? Also higher the concentration of reagent faster the ...
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Use of statistics in this field

I am currently pursuing a statistics course and I an interested in knowing how can statistics help this field in future. (I am interested because I love chemistry very much) Specifically, are there ...
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Can the “rate coefficient” of a chemical reaction really be called a “rate constant”?

Can the rate coefficient of a reaction ever be referred to as a constant? To my limited knowledge, it cannot, because it is dependent on factors such as temperature (I'm getting that info from the ...
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In a 'A + B -> C+D' reaction, A and B have the same initial concentration. find the half life of B given the half life of A

The reaction is A+B -> C+D The initial concentration of A (CiA) is 4 mol/L. The initial concentration of B (CiB) is 4 mol/L. The half life of A (tA1/2) is 20 minutes. Find the half life of B. ...
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chemical kinetics of a reaction, rate constant, activation energy

From the Arrhenius equation in kinetics of reactions, $$k = A\exp{\left(-\frac{E_\mathrm{a}}{RT}\right)}$$ Which tells us about the Temperature dependence on rate constant of a reaction. Activation ...
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Are heterolytic dissociations barrier-less or do they have an activation energy?

When a bond is broken into ionic fragments, and I'm specifically thinking about organometallic or coordination chemistry, the two products carry opposite charges and the potential energy curve should ...
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Mechanism for reaction between hydrochloric acid and magnesium

Balanced equation: $$\ce{Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)}$$ However, Cl- is a spectator ion so the actual reaction equation is: $$\ce{Mg + 2H+ -> Mg^2+ + H2}$$ Here is my proposed ...
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How does changing volume affect concentration of solutions?

My teacher performed an experiment and made us watch. He prepared 3 conical flask containing 50 mL mixture of sodium thiosulphate, potassium iodide and acetic acid. He also had 3 measuring ...
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Chemical kinetics [duplicate]

If I observe any random reaction lets say: aA+bB-->cC+dD And I note down the change in concentration of A with time and try to calculate the rate of reaction,it will be: Rate=-delta(A)/(a×delta(t)) ...
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If the rate law order is three, does that mean that three bodies collide at some elementary step?

I am doing a chemistry review about rates, and I get asked "Which of these statements is false?" The answer is In reactions that are second order in one reactant and first order in another, the ...
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Determining Reaction Orders

Can you figure out the reactant's reaction order (First-order, second-order, third-order, etc.) JUST by looking at a chemical reaction? What if you were given a multi-step reaction? A single step ...
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Units of rate constant (cycles per second vs radians per second) in Eyring equation

In the Eyring equation (EE), $$k = \frac{k_\mathrm B T}{h} \exp\left(\frac{-\Delta G_{\mathrm f}}{RT}\right),$$ the units of $k$ are $\mathrm{s^{-1}}$. However, in general rate constants are usually ...
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When is it permissible to use the stoichiometry of a reaction to determine rate laws?

I have read in a general chemistry textbook that rate laws can only be determined by experiment. This seems intuitive because if a mechanism is not elucidated and tabulated reaction data would be one ...
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106 views

Why dynamic equilibrium exists?

We know that at equilibrium Gibbs energy is minimum. We also know that at equilibrium both forward and reverse reactions occur simultaneously, and also we know that for a reaction to be spontaneous ...
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113 views

Does a reaction have to have a rate determining step?

I am a bit confused about the concept of the rate determining step. From what I understand, a step in a reaction is the RDS if it meets the following requirements: It is the slowest step in a ...
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Which step below is rate determining

What is the rate determining step in the following energy profile? To clarify, the reaction is: A -> B -> C The energy of A is greater than B which in turn is also greater than C. The intermediate ...
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Factors affecting the Activation energy of a reaction

The reactions of different carbonates with HCl have different activation energies. Why do they have different activation energies?
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First order differential equation for transmembrane diffusion

I want to model transmembrane diffusion using a first order reversible differential equation. The diffusion rate is known from literature. There are two volumes $V_{\mathrm{intra}}$ and ...
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Finding [A] when looking for the velocity constant

Some reaction of first order on $[A]$ has the data: What is the velocity constant for this reaction? The units are $s^{-1}$. Well, since the units are $s^{-1}$, then the reaction ...
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Find the velocity constant K given the speed

This reaction is of first order in [A]. Consider that What is the velocity constant $K$ here? So let's see... The velocity equation is $$V = K \cdot [A]^n\cdot[B]^m$$ Assuming that ...
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fractional orders of reaction? [duplicate]

Why do some reactions have fractional orders with respect to an inhibitor or catalyst? For example fluoride ions acting as an inhibitor for the reaction between calcium carbonate and acids.
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How does a reaction exhibit kinetics with a non-integer reaction order?

What does it mean when the order of reaction isn't an integer, e.g., a reaction order of 2.43. Not with something acting as a catalyst but rather as a inhibitor. Why does the inhibitor produce an ...
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What is more acidic: D3O+ in D2O or H3O+ in H2O and why?

What is more acidic: $\ce{D3O+}$ in $\ce{D2O}$ or $\ce{H3O+}$ in $\ce{H2O}$ and why? I think it's $\ce{D3O+}$ in $\ce{D2O}$ as I saw somewhere that this property is used in mechanistic studies ...
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Clash between thermodynamic and kinetic processes

I have often come across reactions where kinetic and thermodynamic processes give completely different outputs. I was told that in such cases check temperature, if temperature controlled, then take ...
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Reaction rate constant conversion

I'm flustered, I'm not into chemistry and need to convert $\mathrm{(nM\cdot s)^{-1}}$ to $\mathrm{(M\cdot s)^{-1}}$. Is it correct to multiply with $10^9$?
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Confusion about the graph plotted from the Arrhenius equation

According to Arrhenius equation $k = A\mathrm e^{(E/RT)}$, where $k$ is the rate constant, $E$ is the activation energy, $R$ is the universal gas constant and $T$ is the temperature. Taking log both ...
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Meaning of steady state (kinetics)

In kinetics, we use the steady state approximation to relate the concentration of intermediates to the concentration of reactants. For example, given the mechanism $$\ce{A->[k_1]B}$$ ...
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Iodate Clock Reaction Concentration

In our chemistry class, we performed the iodate clock reaction. We were finding the rate law for the reaction. We changed the concentration was by taking the same amount of iodate ion solution each ...
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Finding reaction rate law without having information about rates of elementary steps

Say we're given the mechanism of the reaction, and the rate constants of the elementary steps are $k_1,k_2,$ etc. However, if we don't know the values of the $k$s, or several $k$s have similar values, ...
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Activation energy Values

Are there any standard literature values for the activation energies for the reactions: $$\ce{Na2CO3 + HCl -> NaCl + H2O + CO2}$$ $$\ce{CaCO3 + HCl -> CaCl2 + H2O + CO2}$$
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Continuously replenished reaction

Substrate ($m$) concentration in a reaction scheme is governed by the equation $$\frac{dm}{dt} = -\dfrac{r_1c_1m}{1+\dfrac{r_1}{r_2}m + \dfrac{r_1r_3}{r_2r_4}m^2}$$ where $c_1$ is the initial enzyme ...
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How to calculate the rate constant of a zero-th order reaction?

The reactant concentration in a zero-order reaction was $7.00×10^{−2}~\mathrm{M}$ after $160~\mathrm{s}$ and $2.50×10^{−2}~\mathrm{M}$ after $345~\mathrm{s}$. What is the rate constant for this ...
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When using the Arrhenius Equation, beyond what range would the values of k, A , and Ea be extreme

In the Arrhenius Equation $$k = A \mathrm e^\frac{-E_\mathrm a}{RT}$$ with: $k$ defined as the rate constant $A$ as the pre- exponential factor $E_\mathrm a$ as the activation energy (in$\ ...
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How to interpret the activation energy calculated via the Arrhenius equation? [duplicate]

In solution phase, the activation energy of a reaction is usually determined through the study of kinetics and the Arrhenius equation. However, I am confused by the notation, and have trouble ...
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How to interpret the rate constants of in-vivo racemization of thalidomide?

The article by Eriksson et. al. found that thalidomide undergoes chiral inversion in vivo. It found the mean rate constants too, $0.17~\mathrm{h^{-1}}$ (R to S) and $0.12~\mathrm{h^{-1}}$ (S to R). ...