Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
1,086
questions
-4
votes
0
answers
12
views
Rounding when finding the reaction order [closed]
If I were to find the reaction order and the answer is 1.5454281, would I round to 2 or just keep it at one? thanks!
-3
votes
0
answers
30
views
Help with balancing a chemical equation and optimizing reaction rate [closed]
I am having trouble with a chemistry question and was hoping someone could help me out. The question is as follows:
Nickel reacts with hydrochloric acid to form nickel(II) ions and
hydrogen gas.
a) ...
-1
votes
2
answers
64
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 + ...
- 1
0
votes
0
answers
53
views
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}$, ...
- 101
-2
votes
0
answers
29
views
Should the duration of a reaction when determining its rate be considered a dependent or controlled (constant) variable?
I am writing a lab report on rates of reaction and have encountered a problem when it comes to the variables. My group opted for an unorthodox approach: we wanted to see if the rate of reaction ...
- 9
2
votes
1
answer
28
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$...
- 21
-1
votes
2
answers
33
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\...
- 251
0
votes
1
answer
67
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 ...
- 251
-2
votes
1
answer
82
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 ...
2
votes
0
answers
61
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 ...
- 29
0
votes
1
answer
50
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 ...
- 35
0
votes
0
answers
32
views
Does activation energy vary with temperature for the reaction between oxalic acid and potassium permanganate?
I've always been taught that activation energy doesn't vary with temperature for reactions, as $E_A$ represents some specific energy required by particles so that they can react. However, I recently ...
- 181
1
vote
0
answers
116
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 ...
- 35
1
vote
1
answer
114
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 ...
- 181
3
votes
0
answers
51
views
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 ...
- 39
2
votes
0
answers
126
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 ...
- 95
1
vote
0
answers
176
views
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 ...
- 1,562
0
votes
2
answers
82
views
Reaction rate derivation: amount of substance vs concentration [closed]
Let's say you have the reaction
$$A + B \; \rightarrow \; C.$$
I would like to understand why $\frac{\mathrm{d}[C]}{\mathrm{d}t}$ is proportional to $[A][B]$. I can see why
$$\frac{\mathrm{d}n_C}{\...
- 11
1
vote
0
answers
86
views
Difference between pre-equilibrium and steady-state approximation?
Both are reaction mechanisms in which there are several steps and at least one intermediate present. However, I am confused about the differences of both methods, especially when using them to ...
- 45
4
votes
1
answer
50
views
Using a Chi-Square distribution table to calculate fraction of gas molecules with activation energy
I couldn't decide whether to ask this to Chemistry, Physics or Statistics stack exchange. Hopefully I made the right choice.
According to this Wikipedia page, while the speed of particles in an ideal ...
- 155
0
votes
1
answer
195
views
Mechanism of decomposition of N2O5
In my book mechanism of decomposition of $\ce{N2O5}$ was given like
\begin{align}
\mathrm{Reaction:}\\
\\
\ce{2 N2O5 &-> 4 NO2 + O2}\\
\\
\mathrm{Mechanism:}\\
\\
\ce{N2O5 &<=>[k_1][...
- 15
-3
votes
1
answer
78
views
Rate of Reaction and half life [duplicate]
During the course of chemical kinetics while studying zero order or first order they consider rate of reaction to be dependent only on single Reactant
For ex:- A--> product,Rate of Reaction=k[A]^0 ...
- 1
-2
votes
2
answers
61
views
The differential rate law applies to only one single species
In my book it was written that
The differential rate law applies to only one single species, so unless we have equimolar amounts of each reactant or make an approximation using an excess of one, we ...
- 1
1
vote
1
answer
47
views
Can a non-rate determining step control what products form in a reaction?
In Organic Chemistry by Clayden, the stereoselectivity and regioselectivity of the E1 mechanism is explained in terms of the differing transition state energies (and therefore rates) of the possible ...
- 333
2
votes
1
answer
88
views
Reversible monomolecular reaction with two reverse rates
I think this is a simple problem but my kinetics are terrible and I was hoping for some assistance following up on the work of a previous student. I'm open to any form of assistance and I hope this ...
3
votes
1
answer
76
views
Concentration dependence of electron transfer
Regarding a single electron transfer:
$$O +e^- \rightarrow R$$
We find the current dependent on the overpotential as specified by the Butler Volmer equation:
$$i = i_0 (exp(\frac{\eta}{b})-exp(\frac{-\...
- 143
3
votes
1
answer
262
views
Calculating rate constant for reaction between ethyl acetate and sodium hydroxide
My research question is investigating how temperature affects the rate constant for the reaction between ethyl ethanoate (acetate) and sodium hydroxide. I understand that I must titrate sodium ...
- 181
2
votes
1
answer
93
views
Finding a Heterogeneous Catalyst for Hydrogen Peroxide
I'm designing an experiment to test the effect of surface area of a catalyst on the activation energy of hydrogen peroxide decomposition. However, I don't think I can use a powdered catalyst because ...
- 29
0
votes
0
answers
93
views
Temperature dependence of order of reaction
In my textbook, it is given that the order of a reaction can change with temperature and pressure, but examples are not given. One possible explanation for this is that the rates of complex reactions ...
4
votes
2
answers
314
views
Chemical kinetics for cyclic reversible reaction
Find $[\ce{C}]/[\ce{A}]$ for the following system at equilibrium:
I know that at equilibrium
$$\frac{[\ce{C}]}{[\ce{A}]} = \frac{k_{-3}}{k_3} = K_3, \tag{1}$$
but my teacher told me there was another ...
- 89
0
votes
0
answers
53
views
What's the maximum temperature of quicklime slaking?
Normally the maximum temperature of lime slaking is listed at about 100 C. I've read that using water with high salt concentrations will catalyze the slaking reaction and increase the boiling point ...
- 27
1
vote
0
answers
20
views
Crude palm oil DOBI analysis
I'm performing Crude Palm Oil DOBI spectrum analysis using uv-1900i UV-VIS spectrophotometer at a range of 269nm and 446nm but it's only giving peak absorbance at 446nm but no reading at 269nm,what ...
0
votes
2
answers
77
views
chemical equilibrium and activity
Here is a graph of equilibrium coeff in various salt concentrations in water.
Lets take the example $\ce{BaSO4}$.
Now as we are increasing the salt concentration in water, the following reaction is ...
- 289
1
vote
2
answers
99
views
Relation between activation and threshold energies
Activation energy $E_\mathrm{a}$ and threshold energy $E_0$ appear to be equivalent quantities:
In particle physics, the threshold energy for production of a particle is the minimum kinetic energy a ...
- 1,009
3
votes
1
answer
65
views
What is the difference between a single displacement reaction and a two competing reaction system?
For example, consider the single-displacement reaction
$$\ce{AB + C <=> BC + A}$$
My question is then if writing this reaction as the system
\begin{gather}
\ce{AB <=> A + B} \\
\ce{B + C &...
1
vote
1
answer
38
views
Dependence of rate on the nature of reactants and other factors
Consider a reaction
$$\ce{aA + bB -> cC + dD}$$ whose reactants are given by A and B and the products are C and D.
The rate of this reaction is given by $$\frac{dx}{dt} = -\frac{d[\ce{A}]}{adt}= -\...
- 281
-1
votes
1
answer
63
views
How do I interpret the dissolution rate unit? [closed]
I have found a paper (link) that is interesting for my research project.
The dissolution rate unit in this paper is described as $\pu{mol/cm^2/s}$.
For my project I would need the dissolution speed ...
- 19
4
votes
3
answers
211
views
Excited states and emission lifetimes
I have some doubts about the nomenclature of the lifetimes. Are singlet and fluorescence lifetimes the same? As well as the triplet and phosphorescence lifetimes?
Also, can the triplet/phosphorescence ...
- 139
1
vote
0
answers
62
views
Why can we use the arrhenius equation to measure the number of vacancies in a material?
In a materials science video I was watching today the prof. said we could use the arrhenius equation to estimate the number of vacancy point defects in a material. And gave the following equation:
Nv =...
- 121
2
votes
1
answer
78
views
Definition of activation energy
There seems to be contradictions in the definitions of activation energy ($E_a$) stated by different sources. I found two such popular definitions. Before that, I state my understanding of how an ...
- 129
4
votes
1
answer
79
views
Oscillating vs Autocatalytic reactions
Are all oscillating reactions autocatalytic? Or are all autocatalytic reactions oscillating? What's the relation between them? Am I just mixing up different things or are they basically the same?
For ...
- 1,009
3
votes
0
answers
36
views
Exception to the order reaction and stoichiometric coefficient equality in elementary reactions
When a reaction is elementary,the stoichiometric coefficients always equal the order for each reactant? Is there any exception? Because at Ángel González Ureña's Cinética Química it says that this is &...
- 1,009
3
votes
1
answer
102
views
Total vs. Partial derivatives in kinetics
I've recently seen partial derivatives in the velocity definition but in most cases is with total derivatives (infinitesimal change of concentration over infinitesimal change of time).
Maybe is more ...
- 1,009
4
votes
1
answer
217
views
Half-life vs. relaxation time vs. average lifetime
On page 25 of Ángel González Ureña's Cinética química (2001), appear the terms half-life time (of an intermediate) and relaxation time, but it refers to both of them with the letter $\tau$. Why is ...
- 1,009
6
votes
2
answers
953
views
Why can't the half-life be determined in a reaction with more than one reactant?
We have a second order irreversible reaction with 2 reactants (A and B, order 1 for both) so that the initial concentrations are different. I've read that the half-life doesn't make sense in this ...
- 1,009
0
votes
1
answer
85
views
How do we know that rates depend on the product and not the sum of reactant concentrations [closed]
I've been struggling to understand the mathematics behind the calculation in enzyme kinetics within systems biology at an intuitive level.
Every research article and textbook says it is based on the ...
- 117
2
votes
1
answer
133
views
Differential equation in consecutive reactions
I'm blocked in a step of getting to the equation $(7)$, more precisely in the step between $(5)$ and $(6)$. I show my way to solve it down, but I don't get the same as $(6)$, so I wanted to know if I ...
- 1,009
6
votes
1
answer
294
views
Iodine clock reaction: lower temperature but faster result?
I was told by several high school students that they experienced odd results in their iodine clock reaction lab. They did several different trials, and the lower the temperature, the faster the blue ...
- 611
7
votes
2
answers
745
views
Mechanism of the blue bottle experiment
I have researched multiple mechanisms for this experiment yet all of them suggest different versions or are too vague. None of them are consistent since the final overall equation seems to be missing ...
- 73
5
votes
1
answer
345
views
Negative or fractional order of reaction
Let $\ce{A}$ be the reactant and $\ce{P}$ the product at the imaginary elementary reaction $\ce{A->P}$.
Could it possibly have a net total order of $-1?$
$$-\frac{\mathrm d[\ce{A}]}{\mathrm dt} = k[...
- 1,009