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Questions tagged [kinetics]

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

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Effect of presence of competitive inhibitor on observed reaction constant

Suppose there is a solution of enzyme, its substrate, a competitive inhibitor, and a suicide inhibitor. The reaction rate constant for the reaction of the suicide inhibitor with the enzyme is known. ...
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Concentration units for kinetic mechanism of combustion

I am reading Tamás Turányi & Alison S. Tomlin's Analysis of Kinetic Reaction Mechanisms (2015). On page 10-11, the authors state that for a mechanism with $N_R$ reactions involving $N_S$ species, ...
math_lover0105's user avatar
1 vote
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What is the reaction between crystal violet and bleach (sodium hypochlorite) and what is the mechanism of its action against crystal violet?

I'm trying to find the reaction between bleach (sodium hypochlorite) and crystal violet, and need to find the mechanism of its action, as during my lab investigation the bleach did cause the crystal ...
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7 votes
2 answers
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Does stoichiometry matter in extent of reaction calculation?

I was recently introduced to the extent of reaction and learned that it can be calculated using this equation $$\xi = \frac{n_{A,out}-n_{A,in}}{\nu_A}.$$ If I'm using this formula to calculate the ...
Leon's user avatar
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2 votes
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Gibbs free energy of transition and activation energy

Let's consider a reaction A (reactant) -> B(product) and activated complex is denoted by C. This graph ( potential energy vs reaction coordinate ) tells us that reactant need some amount of ...
Bharat Prajapat's user avatar
-4 votes
1 answer
122 views

Is half-life defined for a reaction or for a reactant?

Consider the following chemical reaction. $$\ce{A + B -> Products}$$ If this is a zero-order reaction with respect to $\ce{A}$ and $\ce{B}$, then is there a half-time for this reaction? Or must we ...
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Effect of competitive inhibitor on substrate inhibition

In an enzyme that undergoes substrate inhibition, how would the presence of a competitive inhibitor affect said substrate inhibition? Would the substrate concentration at which substrate inhibition ...
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Does someone know a unique testable questions surrounding 1 of the 5 variables that affect the rate of a chemical reaction? [closed]

I am a year 11 student studying high school chemistry and we are currently studying catalysts. I am working on an assessment and need to come up with a unique but testable hypothesis surrounding one ...
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1 answer
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Why do we consider one elementary reaction to be in equilibrium while calculating rate law for complex reactions?

When we calculate rate of reaction pfor a complex reaction, if the rate determining step have intermediates, we calculate the rate of reaction using the step which is at equilibrium (and doesn't have ...
NOTE Book's user avatar
2 votes
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How are enzyme inhibition constants assayed for "multi-inhibitors"?

Suppose there is a suicide inhibitor of an enzyme that reacts with the enzyme to form an inactive enzyme and another product. This "Another product", however, is capable of acting as a ...
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Non-elementary reactions: Relationship between kinetic and equilibrium constant

As far as I understand, the equation for a kinetic equilibrium is always the same, and is given by: $$K = \frac{\text{concentration of products}^{p}} {\text{concentration of reactants}^{r}}$$ Where $p$...
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Is it a convention to divide rate of reaction by stoichiometric coefficient?

If we consider a reaction $$ \ce{A + B -> 3 C} $$ The rate of reaction is given by $$ R= -\dfrac{\Delta[A]}{\Delta t} = -\dfrac{\Delta[B]}{\Delta t} = \frac13\dfrac{\Delta[C]}{\Delta t} $$ I know ...
Naman Singh's user avatar
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1 answer
86 views

How does the concentration of a reactant change? Is it based on individual order or overall order?

Reaction $\ce{A + B ->[$k$] C + D}$ follows the rate law $$r = k [\ce{A}]^{1/2}[\ce{B}]^{1/2}$$ where $k$ is given. Starting with $1 \,\pu{M}$ of $\ce{A}$ and $\ce{B}$ each, what is the time taken ...
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Why can we use stoichiometric coefficients in the equilibrium-constant expression? [duplicate]

I just studied the chapter on chemical kinetics on Coursera, wherein I was repeatedly admonished not to use the stoichiometric coefficients in the rate law formula. I was told that this formula has to ...
Shoes's user avatar
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3 votes
1 answer
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Why is the decomposition of gas on a metal surface at high pressure considered a 0 order reaction?

My textbook says that when ammonia decomposes on a platinum surface at high pressure, the reaction is 0-order. This is because at high pressures, the metal surface gets saturated with ammonia ...
Harjot Dhillon's user avatar
6 votes
1 answer
263 views

Lifetime components in phosphorescence decay

I'm studying the phosphorescence decay of diacetyl in acetonitrile (it has a high quantum yield of intersystem crossing). The fluorimeter than I'm employing has microsecond resolution and, since the ...
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6 votes
1 answer
234 views

Non-Arrhenius temperature dependence of bimolecular reaction rates at very high temperatures

Once I have read that in some cases bimolecular reactions can exhibit a maximum as a function of temperature due to the short lifetime of the activated complex at very high temperatures. At low ...
YoussefMabrouk's user avatar
3 votes
0 answers
127 views

What is the physical significance of the frequency factor in the Arrhenius equation?

As the title says, I am wondering what the physical significance of the frequency/pre-exponential factor in the Arrhenius equation. My idea of it is that: If the units of $E_a$ are energy per molecule,...
PhysPhil's user avatar
2 votes
2 answers
273 views

Sequential first order reaction graph in chemical kinetics

In graph given below is a sequential first order reaction $$\ce{A ->[$k_1$] B ->[$k_2$] C}$$ For $k_2 \gg k_1$ the graph of concentration of $\ce{A}$, $\ce{B}$ and $\ce{C}$ is as follows. Won't ...
A 10th grader's user avatar
1 vote
1 answer
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Is it possible for a reaction to change its order mid-reaction?

I encountered a problem which stated that the order of the reaction remained zero, until the concentration was halved. Then it became first order. Already, zero ordered reactions don't actually exist (...
Oscillatingdipole's user avatar
3 votes
1 answer
184 views

The isotopic effect in chemical kinetics

I conducted a chemical experiment (degree in chemical engineering) to understand the isotopic effect in chemical kinetics. In the experiment, I reacted isopropanol and D-isopropanol (D stands for ...
Guy Weizman's user avatar
-3 votes
1 answer
129 views

What if kc=1 will reactants concentration equals to product concentration [closed]

I read a book, it says if kc=1 it mean reactant concentration equals to product concentration at equilibrium. But I'm wondering that in kc expression we dont just use concentration of an element we ...
Zayden's user avatar
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1 vote
4 answers
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In a reversible reaction, how can endothermic and exothermic processes happen simultaneously?

A reversible reaction has both the forward and the backward reaction occurring at the same time. I struggle to understand how this is logically possible. One reaction pathway is always endothermic, ...
James's user avatar
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2 votes
3 answers
328 views

Change of equilibrium constant with respect to temperature

Suppose we have an arbitrary chemical reaction $A+B\rightleftharpoons 2C+D$ and its equilibrium constant at two temperatures $T_{1},T_{2}$ are $k_{1},k_{2}$. We can relate them as $$\log\frac{k_{2}}{...
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3 answers
214 views

Approximate calculations of the product distribution under kinetic control

What is the product distribution when the energy difference between the transition states (∆TS = TS1 – TS2), is at 2 kcal/mol and when it is at 5 kcal/mol (assuming room temperature)? I know that 1.4 ...
Saipie's user avatar
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1 answer
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Why are the derivatives of the concentrations divided by stoichiometric coefficients?

Consider this simple dioxygen to ozone chemical equation $$\ce{3 O2 -> 2 O3}$$ with the average rate of the reaction $$r = -\frac{1}{3}\frac{\Delta[\ce{O2}]}{\Delta t} = \frac{1}{2}\frac{\Delta[\ce{...
Proscionexium's user avatar
-2 votes
1 answer
101 views

Mass action law and conservation of mass [closed]

I am starting to learn about the use of mass action law in chemistry. I am doing some exercises to practice. In particular, I am considering the reaction $$2 X \underset{3}{\stackrel{4}{\...
mejopa's user avatar
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-2 votes
2 answers
91 views

What are the differences between the different Rate Equations?

I currently am about to finish general chem 2 so my knowledge is still basic. There are different kinetics and rate equations and im not quite sure I know the differences. Breaking rate of a reactant:...
PepegaAskingQuestions's user avatar
1 vote
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32 views

How do metal hydrides behave in a non-hydrogen closed system?

I am curious about the fundamentals of metal hydrides and how adsorption/desorption works in non-hydrogen systems. My understanding is that the atom ratio M/Hx of the metal hydride is a function of ...
dwgold9's user avatar
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1 vote
1 answer
153 views

Are there exceptions to the rate law for elementary reactions?

According to several authentic sources (for example, ChemLibreTexts), for elementary reactions, the order is equal to molecularity according to the rate law. Example: For an elementary reaction $$\ce{...
ananta's user avatar
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-1 votes
1 answer
148 views

How to write the balanced chemical equation for the system in a rate plot?

I have the rate plot below: I know that $\ce{A}$ and $\ce{B}$ are the reactants, and $\ce{C}$ is the product. The textbook says that the balanced equation is $$\ce{3A + B -> 2C}\\[1em]$$ However, ...
Gabby Han's user avatar
-2 votes
1 answer
138 views

How to find the initial rate of a rate plot? [closed]

In the graph above, how do I find the initial rate of $$\frac{d[A]}{dt}$$ My balanced chemical equation is $$\ce{3A + B -> 2C}\\[1em]$$
Gabby Han's user avatar
2 votes
2 answers
273 views

How does stirring demonstrate a diffusion-controlled reaction?

I was reading about diffusion-controlled reactions, and on the Wikipedia page (Diffusion-controlled_reaction) it says the following: "One classical test for diffusion control is to observe ...
Jack's user avatar
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0 votes
1 answer
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Effect of changing of the concentration of reactants when concentration of the initiator and the concentration of the initial reactant are very small

A + I---> p What happens to the rate of the reaction when the concentration of the reactant is changed in a system that its concentration of its initiator and the concentration of the initial ...
Kavindu Lochana's user avatar
4 votes
1 answer
124 views

Chemical species equations in a kinetic mechanism of combustion

In combustion, for a kinetic mechanism involving $m$ reactions and $n$ chemical species, of the form \begin{align} \begin{cases} \nu_{11}' \mathcal{S}_1 + \nu_{12}' \mathcal{S}_2 + \dots + ...
Somestudent01's user avatar
5 votes
2 answers
896 views

Effect of inert gas on the rate of reaction

Is there a general effect on the rate of reaction of a dynamic equilibrium when an inert gas is introduced at a constant volume? I know that the position of equilibrium won't change, but much like a ...
Pen and Paper's user avatar
1 vote
1 answer
83 views

Effectivness factor for a cylinder

I would like to demonstrate the effectiveness factor of a porous cylinder, for diffusion-reaction (only radial diffusion, 1st order reaction, isothermal, diffusion coeff. is constant, steady-state), ...
Oquai's user avatar
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-1 votes
2 answers
111 views

Confused about underlying reasoning behind reaction quotient/equilibrium constant

I am a high school student taking AP Chemistry. In the unit on chemical equilibrium, there is much emphasis placed on calculating reaction quotients and equilibrium constants using this method: $$aA + ...
Scott's user avatar
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0 answers
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Strange behavior of equilibrium constant when most of the components are solids / pure liquids

Consider the reaction $\alpha A(g) + \beta B(s) +\gamma C(s) +\cdots \rightleftharpoons \delta D(s)+\epsilon E(s)+\cdots $, so the chemical equilibrium constant should be $\dfrac{1}{[A]^\alpha}$, ...
erpxyr2001's user avatar
2 votes
1 answer
39 views

Derivation of Flory's Model for Linear Condensation of Polymers

I'm having some trouble understanding a part of Flory's model for linear polycondensation reactions. In his 1936 paper, he derives an expression for the probability of the existence of a particular $x$...
Justus's user avatar
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-1 votes
2 answers
145 views

Solving for Partial Pressure given first-order decomposition

From my GenChem practice exam: Consider the following reaction: $\ce{C4H8 (g) → 2C2H4 (g)}$ The first-order decomposition of cyclobutane to two molecules of ethene has a rate constant of $\ce{9.20\...
Mailbox's user avatar
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0 votes
1 answer
258 views

How to use Graham's Law to solve for time

A question from one of my GenChem practice exams: "A 3.0 L sample of helium gas was placed in a container filled with a porous membrane. Half of the helium gas effused through the membrane in ...
Mailbox's user avatar
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-2 votes
1 answer
560 views

When does Van't Hoff's reaction rate rule not work?

I have a problem answering a question in my lab report. The question is about the empirical van't Hoff's rule - what does it say and what are its limitations? I managed to find online that the ...
Alien Lobster's user avatar
2 votes
0 answers
217 views

Activation energy of the reaction between magnesium carbonate and hydrochloric acid

I've been working on a project that uses some abnormal methods to calculate the activation energy using only one trial of an exothermic reaction. However now that I've completed the lab, I want to ...
Redmac's user avatar
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0 votes
1 answer
243 views

Order of reaction with and without the presence of catalyst

When ethene reacts with hydrogen to give ethane in the presence of Ni, the order of the reaction is 2, if I am not wrong, please correct me if I am. But if we remove the catalyst, and simply allow ...
SchrodingerCat2023's user avatar
1 vote
0 answers
129 views

On Le Chatelier's principle

According to my textbook, Increasing the concentration of the reactants increases the rate of forward reaction only to reestablish equilibrium (Le Chatelier's principle) But doesn't that also ...
Ahmed Basem's user avatar
1 vote
1 answer
550 views

Calculating rate constant for reaction between potassium permanganate and oxalic acid

I'm writing a lab report investigating the effects of temperature on the rate constant in the reaction between potassium permanganate and oxalic acid. For my practical I've measured the time of colour ...
aayush's user avatar
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3 votes
0 answers
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Equilibrium concentrations of CO and Cl2 by dissociation of phosgene

I am working through a problem set from MIT's open courseware course Principles of Chemical Science. The question is: Phosgene $\ce{(COCl2)}$ is a chemical warfare agent that decomposes by the ...
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2 votes
0 answers
635 views

How does red iron oxide (Fe2O3) increase the burn rate of sugar rocket fuel?

My question is similar to this one, however that question seems to ask about how it improves combustion in general, not specifically with respect to sugar rocket fuel. The answer to this question ...
jb0's user avatar
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2 votes
0 answers
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Which Gibbs' free energy is an activation energy diagram referring to?

In the case of activation energy diagrams in terms of potential energy, I understand that when we're talking about two individual molecules, the potential energy is highest in the transition state ...
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