Questions tagged [kinetics]
The study of rates and steps in mechanisms of chemical processes.
971
questions
2
votes
0answers
14 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 ...
8
votes
5answers
1k 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
22 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
vote
1answer
44 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
votes
0answers
23 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
122 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
69 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
$$\mathrm{rate} = k[\ce{A}]^a[\...
0
votes
1answer
66 views
What happens in a unimolecular reaction? [closed]
Molecularity is defined as the number of molecules required to collide simultaneously to form a product in an elementary reaction.
In a unimolecular elementary reaction, do two molecules of the same ...
4
votes
2answers
568 views
How to estimate the temperature needed to overcome an activation energy barrier?
Trying to elucidate a reaction pathway, I calculated the energies for different transition states possible for that reaction (computational chem. DFT). I found activation free energies ranging from 29 ...
0
votes
1answer
35 views
Why is oil solubility improved in solvents at higher temperatures?
This is in the case of extracting plant oil using a solvent extraction method for the purposes of biodiesel production.
In a paper, it is stated that increased oil yield may be due to the 'increase in ...
2
votes
0answers
32 views
What is the rate constant k for the reaction between potassium manganate and oxalic acid?
For my school's chemistry classes, I am investigating the kinetics of the redox reaction between $\ce{K2MnO4}$ and $\ce{C2H2O4}$. I analyzed the data using a colorimeter set to $\pu{565nm}$. ...
2
votes
1answer
47 views
Finding the rate of a reaction given experimental data for reaction kinetics [closed]
Here is the question:
For the reaction:
$$\ce{2 A + 2 B → C + D}$$
The following data was obtained from three experiments:
\begin{array}{c|ccc}\hline
\bf{Experiment} &\textbf{[A] (mol/L)} &\...
0
votes
0answers
12 views
Confused about what to put as the x, y in the picture regarding chemical kinetics
I don’t understand what I should put as the x, y...I drew...is it a stechiometric coefficient or an order number? The pictures seem conflicting to me. Am I getting something wrong?
5
votes
3answers
240 views
Rate of a reaction when volume of the system varies with time
Background
I was solving this question from this book and I was not able to get any of the options.
The gaseous reaction $\ce{n_1 A_{(g)} -> n_2 B_{(g)}}$ is first order with respect to ‘A’. The ...
5
votes
0answers
89 views
Explanation of the trans-effect (thermodynamic and kinetic) for octahedral transition metal complexes
The thermodynamic trans effect refers to the ground state weakening of the metal-ligand bond in a complex by a ligand trans to it. The kinetic trans effect is the lablisation of a ligand in a complex ...
1
vote
0answers
41 views
How to graph a second order reaction with two different reactants
In a laser flash photolysis experiment, $\ce{C6H5NH2}$ $(C_0 = \pu{60 \mu M})$ is oxidized to the corresponding radical cation. The disappearance of radical cation is monitored spectrophotometrically ...
0
votes
1answer
47 views
Energy per atom in a parallel radioactivity equation [closed]
I was reading an example in my textbook and the question goes like this:
In a parallel radioactive decay, find energy liberated per atom of 'A' in MeV.
The solution is proceeded like this:
$$
\...
5
votes
2answers
90 views
Steady-state approach - how to find rate equation for intermediate?
The reaction mechanism for the formation of $\ce{NO2}$ is:
\begin{align}
\ce{NO + NO &<=>[$k_1$][$k_1'$] N2O2} & &\text{ (slow)} \\[0.2cm]
\ce{N2O2 + O2 &->[$k_2$] NO2 +NO2} &...
3
votes
0answers
52 views
Steady state approximation for three-step cycle
How to write the steady state for $\ce{A}?$
$$\ce{A ->[$k_1$] B ->[$k_2$] C ->[$k_3$] A}$$
Species $\ce{A}$ seems to appear on both side of equation as it uses itself to produce some of ...
4
votes
1answer
164 views
Can anyone explain, why there are coefficients 2 in the equation for rate of change [A]?
The reaction mechanism for the decomposition of $\ce{A2}$ is thought to be:
\begin{align}
\ce{A2 &<=>[$k_1$][$k_1'$] A + A} & &\text{ (fast)} \\[0.2cm]
\ce{A + B &<=>[$k_2$]...
3
votes
0answers
49 views
How to calculate the quantum yield of a photochemical process?
I have that $\pu{100 ml}$ of an aqueous solution containing $\pu{1.0 mM}$ $\ce{H2O2}$, $\pu{100 mM}$ $\ce{CH3OH}$ and $\pu{200 mM}$ DMSO are exposed to monochromatic light with a wavelength of $300$ ...
3
votes
3answers
171 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
$$\...
0
votes
0answers
26 views
Temperature at which the reaction Oxalic acid + KMnO4 becomes autocatalytic
As described many times, the reaction between oxalic acid and potassium permanganate can be autocatalytic due to the production of Manganese ions.
I've read that this only occurs at higher ...
0
votes
1answer
110 views
Does mass affect rate of reaction?
Suppose I am reacting HCl with CuCO3.
Experiment 1: I use 2g powdered CuCO3
Experiment 2: I use 4g powdered CuCO3
All other variables are kept constant.
Will this have any affect on rate of reaction? ...
4
votes
2answers
87 views
Determine vmax and enzyme concentration (Michaelis–Menten)
I am given that the enzyme concentration is $\pu{15 nM}$ and the following data:
$$
\begin{array}{rl}
\hline
S/\pu{mM} & V/\pu{mM s^{-1}} \\
\hline
1 & 0.202 \\
2 & 0.368 \\
5 & 0....
0
votes
0answers
23 views
Radical Chain Reaction, termination steps
In the termination step of radical chain reaction, we often neglect the recombination of hydrogen atom radicals and it will not be included in the mechanism.
Let say the reaction is between $\ce{H2}$ ...
1
vote
1answer
160 views
Which alkene reacts faster with HCl?
Which alkene reacts faster with HCl?
The logic tells me the most stable alkene 2 which is the most substituted would react the slowest.
On the other hand, it would form the most stable tertiary ...
2
votes
1answer
109 views
The effect of dilution on the rate of a system in equilibrium
I'm attempting to answer a question from my textbook, however the answer that the textbook provides doesn't make sense to me.
The question:
Laura, a VCE chemistry student, loves graphs and wanted to ...
6
votes
1answer
210 views
Should rates and rate constants be expressed in terms of pressure or concentration?
If an elementary reaction was conducted in the gaseous phase, say $$\ce{X (g) -> Y(g)},$$ would the formal definition of the rate law be $\mathrm{rate} = kP_\ce{X}$ or $\mathrm{rate} = k[\ce{X}]$?
2
votes
0answers
34 views
Lindemann-HInshelwood mechanism difference between high and low concentration
I have a gas reaction which follows the Lindemann-Hinshelwood mechanism and want to calculate the rate constant at low and at high concentrations of the gas but I find myself stuck at what my next ...
3
votes
2answers
57 views
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?...
4
votes
0answers
52 views
Lindemann–Hinshelwood mechanism for a gas reaction
The effective rate constant for a gaseous reaction which proceeds by a Lindemann–Hinshelwood mechanism is $\pu{1.01E-5 s^-1}$ at a concentration of $\pu{4.6E-6 M}$ and $\pu{2.21E-5 s^-1}$ at a ...
3
votes
1answer
176 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 ...
1
vote
0answers
28 views
Why on changing temperature of a reaction its activation energy and pre-exponenetial factor do not change significantly?
My teacher told me that on changing temperature of a reaction, its activation energy ($E_{a}$) and pre-exponenetial factor ($A$) do not change significantly and hence we can assume them to be constant ...
0
votes
0answers
41 views
What is the literature value of the activation energy of the reaction between iodate and bisulfite?
I explored the Arrhenius equation using the reaction between potassium iodate (containing the IO3- iodate ion) and sodium metabisulfite (bisulfite ion), however I can't find a literature value to draw ...
0
votes
1answer
59 views
Why catalyst does not alter the entropy of a reaction?
In my textbook it is written that "Catalyst does not alter the entropy of a reaction". But why? There is literally no explanation given in my textbook as to why this is true. Could you ...
2
votes
0answers
51 views
Why is the variable on the y-axis of Maxwell's Speed Distribution Curve 'fraction of molecules'?
I came across the following graph in my textbook showing the kinetic energy distribution of the gas molecules in a gas sample. Now, the thing is the textbook is telling that the area under the curve ...
2
votes
1answer
52 views
Finding half-life of a nuclide based on gas release
Full Question: The hydride of an unstable nuclide of a Group IIA metal, $\ce{MH2 (s)}$, decays by alpha emission. A $\pu{0.025 mol}$ sample of the hydride is placed in an evacuated $\pu{2.0 L}$ ...
1
vote
0answers
57 views
Confusion in thermodynamically and Kinetically controlled reaction
I am confused in following reaction:
$\ce{(CH3)2CH-CHO}$ when reacts with conc. $\ce{NaOH}$, will it undergo cannizaro reaction?
According to our professor, It can undergo both Cannizzaro as well as ...
4
votes
3answers
98 views
If all molecules have basically the same KE at a given temperature, why do lighter isotopes evaporate more readily?
One of the proxies used for paleoclimate is the ratio of oxygen-18 to oxygen-16 in ice cores and in sedimentary rocks. The idea is that water molecules with oxygen-18 generally evaporate less readily ...
0
votes
0answers
28 views
Measuring energy required or generated in gasification
The typical equation used to measure heat is as follows:
$q = mcΔT\\
\text{Where, }\\
q = \text{heat} (\pu{J}) \\
m = \text{mass} (\pu{g}) \\
c = \text{specific heat capacity} (\pu{J g^-1 K^-1})\\
ΔT ...
3
votes
0answers
30 views
Why does allosteric binding produce a sigmoidal curve?
Allosteric binding is where the enzyme can be regulated through having ligands bind onto somewhere that is not the active site. This will then induce a conformational change on the active site, hence ...
7
votes
3answers
350 views
Why use Km in catalytic efficiency?
The catalytic efficiency of an enzyme is given by $k_{cat}/k_M$ where $k_{cat}$ is the turnover number, or the number of molecules that can be produced per second per active site of an enzyme.
$K_{M}$ ...
1
vote
0answers
34 views
Does the rate reaction of clock reaction increase over time?
I'm studing the following version of iodine clock reaction, in which, $[\ce{H_2O_2}]_0$ > [ascorbic acid]$_0$
$$\ce{I^- + H_2O_2 -> I_2}$$
$$\ce{I2 + ascorbic acid -> I- + side products}$$
...
4
votes
1answer
112 views
Determine reaction order and reaction rate
In a solution of $\ce{Fe^3+}$ the concentration was measured to be:
$$\begin{array}{c|c}
t/\pu{min} & \ce{[Fe^3+]}/\pu{\mu M} \\ \hline
10\ & 238\\
20 & 227\\
40\ & 206\\
60\ & ...
2
votes
1answer
27 views
Diffusion of multiple gases at once
Graham’s law of diffusion states the rate of diffusion between two gases is inversely proportional to their molar masses. Now, this is helpful when we are focused on two gases. But that is rarely the ...
2
votes
0answers
74 views
Effect of stirring and shaking on chemical kinetics
Why don't we take the effects of stirring and shaking on the rates of chemical reactions? While studying chemical kinetics, I've seen that the rates depend on the concentrations of various species, ...
1
vote
0answers
47 views
Using the steady state approximation in the decomposition of nitramide to determine rate law
$\ce{O2NNH2 (aq) ->[\mathit{k}_1] O2NNH- (aq) + H+ (aq)}$
$\ce{O2NNH- (aq) + H+ (aq) ->[\mathit{k}_{-1}] O2NNH2 (aq)}$
$\ce{O2NNH- (aq) ->[\mathit{k}_2] N2O(g) + OH- (aq)}$
$\ce{H+ (aq) + OH-...
3
votes
1answer
62 views
Are the orders of reactants with respect to a reaction different for different starting concentrations?
If the reaction is repeated with $\pu{2 M}$ ethyl iodide the pyridine concentration decreases as shown below. Give the rate law of the reaction in terms of pyridine and ethyl iodide. Explain your ...
4
votes
0answers
33 views
What do the phase space and slope fields of the iodine clock reaction look like?
The iodine clock reaction is a fun experiment shown to undergraduates to illustrate that chemical reactions can show periodic behaviour. Presumably, or hopefully, there is a system of differential ...
