Questions tagged [kinetics]

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

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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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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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33 views

What is change in enthalpy in energy profile? [closed]

Consider an energy profile diagram. My doubt is that why does change in potential energy (PE) equal change in enthalpy here? At constant pressure change in enthalpy equals the net heat exchanged ...
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1answer
141 views

Current in a Lithium Ion Battery

I am trying to find the current transferred to the anode and cathode of a Lithium Ion Battery at different voltages. I know the temperature (approximately) of the battery, the battery's starting ...
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2answers
65 views

Why is oil solubility improved in solvents at higher temperatures?

This is in the case of extracting plant oil using a solvent extraction method for the purposes of biodiesel production. In a paper, it is stated that increased oil yield may be due to the 'increase in ...
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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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27 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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81 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 ...
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1answer
83 views

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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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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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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300 views

Is the rate of a zero order reaction always independent of the concentration of its reactants?

Consider the following reaction : $\ce{A + B}$ $\rightarrow$ $\ce{Products}$ where order of the reaction w.r.t. $\ce{A}$ is $-1$ and order of the reaction w.r.t. $\ce{B}$ is $+1$. So, overall order of ...
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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
128 views

Relationship between molecularity and the reaction order

Should the molecularity be equal or less than the reaction order? Consider the reaction: $$\ce{H2(g) + I2(g) → 2 HI(g)}$$ If we consider the mechanism of this multi-step reaction, the molecularity is ...
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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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1answer
72 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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1answer
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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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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
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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2answers
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Do coefficients matter in rate law?

For reaction $\ce{2A→B}$ (elementary step), according to the rate law, rate $= k [A]^2$. In some calculations, we use $k[A]^2$ as the production rate of B. Why isn't it ${1 \over 2} k[A]^2$? In this ...
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Chemical kinetics of a reversible reaction

I am having trouble with the following question: Consider the following reversible reaction in which the reaction is first order in both directions: $$\ce{[A] <=> [B]}$$ $k_\mathrm a$ is ...
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101 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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23 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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2answers
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How can you qualitatively tell when the hydrolysis of aspirin is over?

I'm doing an experiment on the effect of temperature on the time taken to produce acetic acid and salicylic acid. Are there any qualitative observations I can make about when the reaction has finished?...
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137 views

Concentration and Half Life of reactants A and B

$3.12$ A reaction $\ce{A + B ->C}$, follows first order kinetics with respect to each reactant, with an overall rate constant $k=\pu{2.0 x 10^{-3} M-1s-1}$, the initial concentrations of A and B ...
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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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49 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 ...
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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 ...
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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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1answer
969 views

Relationship between equilibrium constants of a multi-step reaction [closed]

If a reaction proceeds in steps, is the equilibrium constant of every step taken into account to arrive at the final constant? Or can we just calculate equilibrium constant for the overall reaction ...
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4answers
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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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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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1answer
619 views

How would you measure the rate of this SN1 reaction?

I am performing the following $\mathrm{S_N1}$ reaction: $$\ce{t-BuOH + HCl -> t-BuCl + H2O}$$ I would also like to measure the rate of this reaction, but I cannot seem to find a way. I initially ...
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1answer
127 views

Replacement for Centrifuge in Calcium Content Determination

Basically, I'm performing a lab investigation to determine calcium content in different milk sorts. Since my school didn't have any EDTA, I'm using Sodium Oxalate to form a precipitate with Calcium ...
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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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1answer
330 views

p-Nitroaniline reaction with sulfuric acid

An alternative version of the well-known demonstration carbon snake (the dehydration reaction of sugar by concentrated sulfuric acid forming a column of graphite) consists in mixing paranitroaniline ...
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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
127 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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3answers
274 views

Correct Rate Equation for a Reversible Reaction

I'm helping my son with Matlab as he is having trouble learning differential equations as they apply to chemical kinetics. His task is to solve for the equilibrium concentrations for a reaction $$\...
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1answer
72 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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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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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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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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1answer
129 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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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 ...
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1answer
654 views

Solution to the rate law of first order reaction followed by second order reaction (consecutive)

I'm trying to derive the rate law of a first order followed by second order consecutive reaction: $$ \frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t}=-k_1[\ce{A}]$$ $$ \frac{\mathrm{d}[\ce{B}]}{\mathrm{d}t}=k_1[...

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