Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
1,009
questions
2
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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 ...
-1
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0answers
53 views
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{...
2
votes
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 ...
2
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0answers
34 views
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 ...
-2
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0answers
42 views
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 ...
1
vote
0answers
44 views
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 ...
-1
votes
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}{\...
0
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0answers
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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2answers
67 views
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, ...
5
votes
2answers
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 ...
3
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0answers
52 views
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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0answers
39 views
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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0answers
21 views
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 ...
2
votes
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 ...
1
vote
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.
...
0
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1answer
40 views
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}{\...
4
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0answers
50 views
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 ...
0
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0answers
23 views
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 ...
9
votes
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 ...
2
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0answers
28 views
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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0answers
20 views
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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0answers
20 views
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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0answers
33 views
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'...
2
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0answers
32 views
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 ...
0
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0answers
11 views
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
37 views
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 ...
1
vote
0answers
86 views
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 ...
1
vote
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:
$$...
0
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0answers
38 views
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 ...
2
votes
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 ...
0
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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 ...
0
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0answers
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 ...
4
votes
1answer
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 ...
0
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0answers
52 views
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 ...
0
votes
0answers
29 views
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}$$
where $\ce{A}$ is a molecule which collides with another molecule $\ce{M}$. $\ce{A^*}$ is the $\ce{A}$ molecule ...
0
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0answers
51 views
Why we are dividing rate of reaction with respect to a species by its stoichiometry coefficient to find rate of that particular reaction
If there is a reaction like this
$$\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{...
2
votes
0answers
32 views
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 ...
2
votes
0answers
35 views
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:...
8
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4answers
230 views
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}...
0
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0answers
34 views
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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0answers
29 views
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 ...
4
votes
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 ...
2
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0answers
16 views
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 ...
11
votes
5answers
2k views
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 ...
0
votes
1answer
27 views
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 ...
1
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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
...
0
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0answers
24 views
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 ...
2
votes
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 ...
0
votes
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[\...
