Questions tagged [kinetics]

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

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Why does cyclopentadiene react faster than cyclohexadiene in Diels Alder reactions?

How does the length of the bridge of the resulting bicycle change the rate of the Diels Alder reaction (examples below)? I can't seem to think of how one would be more electron donating than the other ...
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What is meant by the rate of reaction, exactly? [duplicate]

In a reaction, say: $$ \ce{aA + bB-> cC + dD} $$ The rate of 'disappearance' of A is $\frac{-dA}{dt}$, while that of B is $\frac{-dB}{dt}$. Similarily the rates of formation of C and D are $\frac{...
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3answers
102 views

Why does increasing electrolyte concentration increase the rate of electrolysis?

I'm a Chemistry teacher and have students who are performing an experiment to determine the effect of copper ion concentration on the rate of solid copper formation at the cathode in an electrolytic ...
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When should the Steady State Approximation be used?

In class, I learned that we should use the steady state approximation when there are multiple slow steps or if the rate determining step is not known (shown on this Chem Libre link). However, further ...
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In the question given below based on the concept of Chemical kinetics

In the following reaction: $$\ce{N2(g) + 3H2(g) -> 2NH3(g)}$$ The rate of appearance of $\ce{NH3}$ is $\mathrm{d}(\ce{NH3})/\mathrm{d}t = \pu{1.7 kg/h}$. The rate of disappearance of $\ce{H2}$ will ...
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Which theory could describe rate constant for photodissociation?

I am considering photodissociation reactions and want to find an appropriate theory to describe how one could determine the rate constant. I know Rice-Ramsperger-Kassel-Marcus (RRKM) theory is for ...
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1answer
63 views

Writing rate of disappearance and rate of appearance using rate law [closed]

I have studied that rate of disappearance and rate of appearance is the change in concentration of reactants and products (respectively) with respect to time. Thus, $$\text{ROD} = -\frac{\Delta c_R}{\...
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38 views

Assuming 2O3 (g) → 3O2 (g), how much oxygen will be formed within 5.50 s for a reaction rate of 0.250 M/s?

Context: The rate of appearance of $\ce{O2}$ in the reaction: $\ce{2O3 (g) -> 3O2 (g)}$ is $\pu{0.250 M/s}$. So, over the first $\pu{5.50 s}$, will it form $\pu{1.38 M}$, or $\pu{4.13 M}$ of oxygen ...
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What is the rate law of a reaction: 2A + 3B → products?

Update: I found out that the coefficients of the chemical reaction are not the exponents in the rate law. It is actually the order of the species during the reaction. It is known that in the reaction, ...
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145 views

Dissolution of sugar in water and its temperature dependence

As far as I can remember, I was taught in 6th grade that warm water would dissolve sugar with greater ease than cool water. In 11th grade, I was taught that Hydrogen Bonding is the reason behind ...
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How long would atmospheric oxygen last on Earth if plants stopped making it? [closed]

A few years ago a rather dubious paper appeared in a mathematical biology journal. The gist of it was that warming oceans could stop oceanic plankton making oxygen (according to a somewhat simplistic ...
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Bond frequency vs Bond Strength in Kinetic Isotope Effect

I am confused by the following: in Ansyln's Modern Physical Organic Chemistry, a higher vibrational frequency defines a stronger bond due to the deeper/sharper potential well (page 76). However, the ...
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Doubt regarding the overall order of a reaction

Suppose their is a 1st order reaction A+B-->C Order with respect to A=2 Order with respect to B=-1 Then it is written in my book that "having order 1 means increasing the concentration of ...
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2answers
127 views

Reaction kinetics of exothermic reaction

A colleague said we can’t dissolve a salt (whose solvation enthalpy is exothermic) faster if we increase the temperature (the solubility equilibrium product is not reached) because Le Chatelier‘s ...
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1answer
62 views

Is the rate-determining step equal to or the lower limit of the overall reaction rate?

I’ve heard many conflicting points on this single question alone. Even the usually reliable sources I run to are pretty ambiguous on the matter. So now I’m here, after 1 and a half weeks of confusion. ...
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1answer
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How to relate equilibrium constant and equilibrium conversion?

For the following gas phase reaction: $$ A\leftrightarrow B $$ The concentration equilibrium constant ($K_c$) can be expressed as: $$ K_c = \frac{c_B}{c_A} = \frac{\frac{F_B}{\vartheta}}{\frac{F_A}{\...
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Briggs-Rauscher reaction doesn't oscillate and turns blue with Vitamin C

I tried to recreate the Briggs-Rauscher reaction by using a solution of $\ce{H2O2}$, $\ce{KIO3}$, $\ce{H2SO4}$, $\ce{CH2(COOH)2}$, $\ce{MnSO4}$ and a soluble starch. I used this recipe. In container ...
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Bromine Clock reaction

Why doesn't the bromine react with the methyl red at the start of the bromine clock reaction? I assume the rate of reaction (and rapid removal) of bromine with phenol is much, much, much faster than ...
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2answers
404 views

True or false: "If a reaction has a large negative value of ∆G, then it will be a fast reaction."

I recently took a Gen. Chem. 2 exam that contained this question. I answered false, as I knew that thermodynamics and kinetics are separate matters. My professor said the answer is true. I pressed him ...
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Relationship between thermodynamics and steric hindrance in reaction outcomes?

I am investigating reactions with alkyl-substituted amines ($\ce{R} = \ce{Me}, \ce{Et}, \ce{^iPr}, \ce{^tBu}$) and a second reagent, in which product Z is formed. $\Delta G$ for all of these ...
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Will increasing the temperature of solid reactants increase rate of reaction?

When temperature of aqueous and gaseous reactants increase, the rate of reaction increases since the particles will move more quickly so frequency of effective collision increases. But does this work ...
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Why doesn’t the amount of ligand needed to reach a fraction-bound value of 0.5 increase as the starting protein concentration increases?

In a Kd binding curve of fraction-bound on the y-axis and ligand concentration on the x-axis, it’s known that the Kd is equal to the ligand concentration [L] needed for [PL]/[Ptotal] =0.5. However, I’...
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Modified Arrhenius equation in the presence of a heterogeneous catalyst

Suppose we are doing heterogeneous catalysis, for example, between nitrogen and hydrogen to create ammonia in the presence of a solid catalyst, like rhuthenium. It's obvious that the gas molecules don'...
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Maintaining our supersaturated oceans

Supersaturates solutions can be unstable and decay beautifully once a seed crystal is introduced. Our oceans near the surface are supersaturated with respect to calcium carbonate. This map shows the ...
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Surface-water hydrolysis reaction & reaction/adsorption kinetics model

I didn't major in Chem or Chem Eng when I was an undergraduate, so I have a rather limited background in this field, please forgive me if my questions are too basic or very wrong. I wish to model a ...
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1answer
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Does pressure affect rate constant? [duplicate]

I would like to know if pressure affects rate constant. Suppose pressure affects the rate constant. Does it depend on partial pressure (like: if I add an inert gas to the system), or only increasing ...
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TCP and KCP product [closed]

Q: According to me, the kinetic controlled product(KCP) should be While the Temperature controlled product(TCP) is: What should be the answer to this question because no temperature has been ...
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1answer
79 views

How does the rate equation account for solids and liquids?

The question is long because I wanted to include the whole thought process. Given the hypothetical reaction: $$\ce{ A(s) + B(aq) <=> C(aq) + D(aq)}$$ One would obtain the equilibrium constant: $$...
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Rate of Decomposition of Sodium Thiosulphate

I want to calculate the activation energy of the decomposition of sodium thiosulphate, as a part of my school research project. I am aware that I must use the Arrhenius equation where the rate of ...
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1answer
77 views

How does the boiling point of water inside a pressure cooker change with temperature? [closed]

My question is why a pressure cooker would affect the boiling point at all. To my understanding, the boiling point of a substance is defined by 'The temperature at which the vapor pressure of the ...
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1answer
33 views

why is $f_{ES}=\frac{[S]}{[S]+K_M}$

I'm working my way through the chapter on enzymes in "Biochemistry" with Stryer et. al, 9th edition. In the current paragraph it's claimed that the fraction of active sites bound to ...
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1answer
118 views

Can an elementary reaction have zero order?

I am very confused right now about my approach to this question could somebody help me out with this. I reasoned my answer as given below Let's assume if a complex reaction is of zero order. It ...
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24 views

Time between hoops appearing in a non-stirred BZ reaction

From what I know, if you start a Belousov-Zhabotinsky reaction in a petri dish, instead of the mixture changing color, hoops would appear periodically. But I can't seem to find anywhere, is there a ...
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119 views

Comparing Rate of Hydrolysis of Acyl halides

In this particular question, my answer is (D) as steric hinderance is minimum there, but answer (B) was given due to the electron withdrawing (-M) effect of the nitro group. Isn't steric hinderance ...
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Ease of reaction of hydrogen with alkali and alkaline earth metals

The ease of reaction of group 1 metals with hydrogen decreases as we go down the group. But why lithium requires high temperature than sodium, potassium and rubidium? What is exactly "ease of ...
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Number of gas molecules in activated state vs normal state

I have a simple bimolecular reaction $$\ce{A + M <=>[k_2][k_1] A^* + M}\tag{1}$$ where $\ce{A}$ is a molecule which collides with another molecule $\ce{M}$. $\ce{A^*}$ is the $\ce{A}$ molecule ...
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Why we are dividing rate of reaction with respect to a species by its stoichiometry coefficient to find rate of that particular reaction

If there is a reaction like this $$\ce{ H2 + Cl2 -> 2HCl}$$ I can understand that each individual species (reactant or product) can have different rates and we can compare them like this, $$-\frac{...
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Can an alloy catalyst change during a reaction?

I am studying the reaction pathway of oxygen evolution reaction (OER) on a PtNi alloy catalyst using density functional theory (DFT). What I found is that, for different intermediates, the most stable ...
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Do decomposition potentials change during electrolysis?

I was just wondering if decomposition potentials actually change during electrolysis. For example, if we reversed the Daniell cell reaction so that copper is oxidized, the half cell reactions would be:...
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Deriving kinetic equations for reversible reactions

Problem Given the reaction $\ce{A <=>[$k_\mathrm f$][$k_\mathrm b$] B}$ with rate constants $k_\mathrm f = \pu{4E-2 s-1}$ and $k_\mathrm b = \pu{10^{-2} s-1}$. Initially, $\pu{2 mol}$ of $\ce{A}...
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Are catalyst concentrations included in the rate expression?

I have seen different rate expressions, some which include the concentration of the catalyst as a term in the rate expression, and others that do not. I thought the rate expression only includes terms ...
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Is there a easy way to estimate how quickly something will dissolve depending on its surface area?

How exactly does the surface area of a solid for example a cube of sugar, affect the speed of its solvation. I guess everyone has observed that a batch of fine grounded sugar or salt dissolves much ...
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1answer
129 views

What is an intuitive explanation for the exponential form in the Arrhenius equation?

What is an intuitive explanation for the exponential form $\exp(-\Delta E/(kT))$ in the Arrhenius equation? While I know the reaction rate theory, I am puzzled by the origins of the form of the ...
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How practically to determine dispersion's Hamaker constant using CCC?

I know that Hamaker constants can be determined from CCC data. $$ccc=\frac{9.85 \cdot 10^4 \epsilon^3 k_B^5 T^5 \gamma^4}{N_A e^6 A^2 Z^6}$$ Where, $\epsilon$ is solvent dielectric constant, $N_A$ is ...
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Are pseudo-zeroth order reactions possible?

Are pseudo zeroth-order reactions possible? I have been taught that pseudo first-order reactions take place and they can be considered pseudo zeroth-order reactions because one reactant is in excess ...
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1answer
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How is the equilibrium expression (law of mass action) related to the rate law? [duplicate]

Every chemistry textbook I've read will have a chapter on the rate law. It will say something like, given a reaction $a\text{A} + b\text{B} \rightarrow c\text{C} + d\text{D}$, the rate law (for the ...
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1answer
48 views

Is there any relation between reaction quotient and rate constant in the context of order of the reaction?

How many times will the rate of the reaction $$\ce{2 A + B -> A2B}$$ change if the concentration of substance $\ce{A}$ is doubled and that of substance $\ce{B}$ is halved? The given solution takes ...
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Why is the concentration of gases denoted in form of partial pressure? [duplicate]

In most of the chemical laws of chemistry involving concentration of products or reactants like equilibrium constant, reaction quotient, Henry's law, Nernst equation etc, I often see a similar note ...
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1answer
131 views

Can't fit an exponential curve to the decomposition of hydrogen peroxide

I have carried out an experiment on the $\ce{MnO2}$ catalyzed decomposition of hydrogen peroxide. I would have expected the reduction in concentration to be exponential but when I fit an exponential ...
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1answer
86 views

How do the terms in a rate law relate to effectiveness and number of collisions of reactants?

In chemical kinetics, we use rate law to find the instantaneous rate of reaction. Let us consider a simple reaction $$\ce{aA + bB -> products}$$ where the rate law is $$\mathrm{rate} = k[\ce{A}]^a[\...

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