Questions tagged [rate-equation]

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PFR reactor: -1/r vs conversion plot

A generic reagent A is considered. The behavior equations of a CSTR reactor is the following: $$ \tau = c_\mathrm{A,0} \intop_0^{X_\mathrm{A,final}} \dfrac{1}{-r_\mathrm{A}} dX_\mathrm{A} $$ where $\...
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Serial reactions or consecutive reactions: rate vs time

Serial reactions, or consecutive reactions, are two or more reactions in which the product of the first reaction becomes the reactant in the next. The simplest case of a serial reaction involves a ...
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Why is the reduction of iron oxide to iron considered a first order reaction where the chemical reactions hints at a second order reaction?

The general reduction of iron oxides is the following according to (Whiston et. al., 2021): $$ \ce{FeO + CO -> Fe + CO_2} $$ The rate law would then convert to: $$ \frac{d[\ce{Fe}]}{dt} = \frac{d[\...
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How does the stoichiometric coefficient affect the time until a given percentage of the reactant is consumed (if at all)?

Problem from Serway's College Physics test bank: The reaction $2NO_2\rightarrow2NO+O_2$ obeys the rate law: $\large \frac{\Delta[O_2]}{\Delta t} = (1.40\times10^{-2})[NO_2]^2 \space at \space 500^\...
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How to rewrite kinetic mass balance to get to proper SI units?

Suppose from kinetic mass balance I get the following differential equation of the molarity substances $A$,$B$, and $C$ in a reactor, with molar in- or outflow rate $\phi$, and rate constant $k$: $$ \...
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What are the reaction rate constants, or coefficients, of coal combustion at high temperature?

Say I have coal that I will combust with $\ce{O2}$ at a high temperature of $\pu{1600-1800 K}$, what are the reaction rate constants, or coefficients, of the main reactions? I have searched around ...
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3 answers
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In regards to the Gibbs free energy equation, it seems that the two terms oppose one another, Enthalpy and -TS. Can you explain this?

So for example, if H is endothermic, then the enthalpy term is positive, meaning energy is absorbed by system overall, meaning net bonds broken, meaning the equation leans towards nonspontaneity. If ...
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Rate order when the slow step only contains intermediates?

I feel a bit sheepish asking this, but I was told that the stoichiometry of the slow step of a mechanism indicates the order of a reaction with respect to a reactant. However, in the slow step of this ...
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Modelling barrier-less reactions

I am currently exploring a few dissociative reactions whose PES is barrierless (no first order saddle point). I have found a few approaches in literature like flexible nudged elastic band theory, ...
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Calculate the concentration of the reactant from the absorbance of the product without molar absorptivity

Given the reaction $\ce{A->B}$, where the absorbance of the product $\ce{B}$ has been measured (see the table below), and the initial concentration of $\ce{A}$ is $\pu{10^{-4} M},$ calculate the ...
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Calculate rate constant of second order reaction and pseudo first order reaction

The reaction A + B -> Prod follows the second order kinetics. In an experiment, you initially have ten times as much B as A. The concentration of A varies with time according to the following data: ...
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pH for optimal kinetic for enzyme reaction

If I am given the following enzyme reaction: where K$_{EH,1}$=K$_1$ = $10^{-4}$ and K$_{EH,2}$=K$_2$ = $10^{-8.2}$. Iwant to calculate at which pH I have the optimal kinetics by calculating $\frac{v'...
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Calculating ionic strength at different concentrations

Zn$^{2+}$ reacts with a molecule, B, in a solution at several different concentrations of NaCl. Determine the charge of the biomolecule and k$_0$ (second order) ​​(assume that Zn$^{2+}$ does not ...
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Tmax of parallel reactions/Steady state reactions

Below are four reactions, to this experiment inhibitor is added so that k$_3$ = $0$ (but the other reactions are unaffected) calculate [D] when the reaction is over. The initial concentration of A is $...
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Why is it that first order reactions never end? [duplicate]

I'm studying chemical kinetics in high school. We are studying Integrated Rate Equation of first order reactions - their derivations and graphs. Our teacher showed us a graph of: Concentration of ...
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How to calculate rate of carbon dioxide from rate equation? [closed]

The concentration of carbon dioxide that changes with time: $$\ce{CO2(g) + H2O(l) <=>[$k_\mathrm{fwd}$][$k_\mathrm{rev}$] HCO3-(aq) + H+(aq)}$$ How to calculate the integral for the following ...
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Can two 1st order reactants in an overall 2nd order reaction have different rates?

I've recently done a saponification reaction of ethyl acetate with sodium hydroxide and used the initial rates method to find the order of reaction. (I change the concentration of one reactant and ...
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-1 votes
1 answer
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Rate equation for the decomposition of hydrogen peroxide with iron(III) chloride as catalyst [duplicate]

I am trying to determine the activation energy of the decomposition of hydrogen peroxide with iron(III) chloride added as a catalyst. To do that, I need to find the rate constant, but I am not sure ...
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3 votes
2 answers
162 views

Does 'k' in the rate law change with a change in volume

I'm a high school AP Chem student and we recently learned about the rate law and the Arrhenius equation. In school, we learned that rate constant 'k' is only changed with temperature or catalyst. ...
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How can gradient of concentration-time graph be zero at equlibirum if the rate of reaction is non zero?

The rate of a reaction is usually measured as the rate of change of the concentration of a reactant or product with respect to time. Also, at equilibrium, the rates of the forwards and reverse ...
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Rate of Reaction - Potassium Permanganate and Hydrogen Peroxide

I'm interested in an aerospace project that requires I know the reaction rate ($[\pu{M/s}]$) of, $$\ce{2 KMnO4 (aq) + 3 H2O2 (aq) -> 3 O2 (g) + 2 MnO2 (s) + 2 KOH (aq) + 2H2O (l)}.$$ I'm just ...
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9 votes
1 answer
250 views

Are there any genuine, elementary ternary reactions?

Macroscopically, reaction rates can be of varied order. But mechanistically, most reactions are first-order or second-order/binary (e.g. SN2, many catalyst surface reactions, dimers). Most processes ...
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1 answer
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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}{\...
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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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-1 votes
2 answers
641 views

What is the rate law of a reaction: 2A + 3B → products? [closed]

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, ...
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1 answer
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Problem understanding the rate of reaction of reversible reactions

Case 1: $$\ce{CH_3COOH + NaOH<=>CH_3COONa + H_2O}$$ At equilibrium, there remain extremely small concentrations of the reactants (acetic acid and sodium hydroxide), and comparatively large ...
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The Mechanism of Termolecular Reactions

How does a termolecular elementary reaction happen under the law of mass action? My physical chemistry textbook only says details about bimolecular and unimolecular reactions with collision theory. I ...
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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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Calculate concentration of product after time passed

If I have two parallel reactions: A --> P$1$ (k$_1$ = $0.00010$ s$^{-1}$) A --> P$2$ (k$_2$ = $0.00050$ s$^{-1}$) and know that the initial concentration of A is $0.0417$ M. How can I ...
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Calculating the concentration of reactants and products in parallel reactions after a time t

A substance A reacts with a solvent B to form an intermediate product IP. The reaction is bimolecular. The conc. of the solvent is constant at $12$M. IP can then react to form the two products P$1$ ...
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Determining reaction order from absorbance

A reaction is initiated in a solution which contained a dissolved component. The transmittance was measured at $\pu{240 nm}$ in a $\pu{2.54 cm}$ long cell. At $t = 0$ the transmittance was $1$. $\...
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Determining ion charge using rate constants and ionic strength

I am given the following data: The rate constant $k$ at $\pu{25 ^\circ C}$ in a reaction of persulfate ions and iodide ions in a water solution is assumed to vary with the total ionic strength of the ...
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8 votes
4 answers
278 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}...
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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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5 votes
2 answers
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Why do alkenes (olefins) burn hotter than alkanes (paraffins), even though alkanes are denser and more hydrogen-rich?

Burning hydrogen releases more total energy than combusting carbon, and all alkanes are denser as well, so why are flame temperatures for alkene molecules higher than their equivalent alkanes? P.S.: ...
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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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1 answer
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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)} &\...
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5 votes
2 answers
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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} &...
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3 votes
0 answers
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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 ...
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4 votes
1 answer
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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 &<=>[$k_2$]...
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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? ...
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4 votes
2 answers
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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....
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3 votes
1 answer
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First or second order reaction

I have that $100$ mM of K$_3$Fe(CN)$_6$ is dissolved in equimolar of the organic ion (which I assume is HCN). In the solution Fe(CN)$_6$$^{3-}$ reacts to form Fe(CN)$_6$$^{4-}$. The formation of Fe(CN)...
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3 votes
1 answer
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Can the RDS be different in different direction in a multi-step reversible reaction?

The following mechanism is given in Peter Sykes when they are "talking about de-esterification" of an ester where the alcohol part is bulky- Here the second step is given as RDS. According ...
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2 votes
0 answers
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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 ...
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4 votes
0 answers
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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 ...
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2 votes
0 answers
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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, ...
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1 vote
0 answers
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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-...
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2 votes
1 answer
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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 ...
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