The study of rates and steps (mechanisms) of chemical processes.

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Why are methanol flames less visible than other flames?

The combustion of methanol tends to generate flames that are less visible than the flames generated by the combustion of other substances? My guess is that methanol burns quickly as it has a ...
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1answer
32 views

Where can I find Equilibrium Constants?

When trying to develop mathematical models to show the concentration in a reaction, where can one find a database or good source of known equilibrium constants if it is not necessarily very convenient ...
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23 views

Can a multi-species system oscillate around equilibrium?

In reading about chemical oscillations such as those that occur in the Belousov–Zhabotinsky reaction (BZ), it's often reported that these reactions were initially not taken seriously, because of a ...
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1answer
29 views

Rate-determining step and steady state approximation failure

1) When can't the rate-determining step be applied, and why? How do you recognize these cases? 2) When can't the steady state approximation be applied, and why?
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2answers
22 views

What is the correct definition of the Gibbs free energy of activation?

Is the following correct? Gibbs free energy of activation is used in energy profiles where the stabilities of the species are expressed as changes in Gibbs energy, while the activation energy Ea ...
2
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0answers
23 views

Analytically combining Dynamic Equilibria that have a two way affect?

Lets say I want to model a water system as the following set of equilibria: $\ce{H2O <=> OH- + H3O+}$ | $\ce{A=[OH^{-}][H3O+]}$ $\ce{CO2 + H2O <=> H2CO3}$ | ...
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3answers
97 views

Why is the equilbrium constant expressed the way it is?

Why are the two molarity's multiplied and not added and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply ...
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3answers
86 views

Rate-limiting in transition state theory

Suppose an initial state $A$ can transition to either state $C$ or state $D$. Suppose further that both of these two processes are rate-limited by a transition to the same intermediate state $B$, as ...
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1answer
36 views

Relationship between rate equation and equilibrium constant

I have read mannaia's answer on the question of 'rate order and confusion', as well as Nicolau Saker Neto's answer to a related question. They have both been very helpful. As I understand, the ...
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1answer
128 views

Kinetic and Thermodynamic Stability

My prof noted that if the two components of any ionic compound undergo a large extent reaction with each other, then the substance CANNOT exist as a pure substance. For example, consider ammonium ...
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1answer
39 views

Formation Constants; Lewis Acidity

I still distinctly remember reading about how Lewis acidity/basicity was characterized using kinetics. The reason given was that because formation constants are so large, these reactions are not ...
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3answers
41 views

What are the units for m in the average kinetic energy formula?

For the equation $E_k=\frac{1}{2}mu^2$ what does the $m$ variable represent? I would say mass but the textbook does not say explicitly that it is anything.
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4answers
83 views

What is reactivity really, and can it be quantified?

I understand the concept of a reactive species on a sort of vague and intuitive level: a reactive species is one that has lots of reactions that it can participate in. These tend to have large kinetic ...
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2answers
58 views

Plot of Arrhenius Equation with temperature

I saw the plot of Arrhenius Equation Here It is a concave upwards graph, but acc to the equation $k= A e^\frac{-E_a}{RT},$ it is evident that the graph is of the form $y= e^\frac{-1}{x}.$ I ...
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1answer
67 views

Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

Take for instance the rection $$\ce{H2(g) + I2(s) -> 2HI(g)}$$ The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a constant, ...
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1answer
67 views

Finding overall order of reaction

Recently I've been going through an exercise of Chemical Kinetics and Nuclear Chemistry and right now I am stuck to one. Question was previously asked in JEE(Advanced)-2013. The question says, In ...
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1answer
37 views

Activation Energy in Acid/Base reactions

For simple acid/base reactions - i.e. those involving inorganic compounds - does activation energy ever play in reactions? Or can we ignore kinetics entirely and just consider thermodynamic factors ...
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2answers
54 views

Does this activation of carbonyls usually involve a SN1 or a SN2?

The process I have seen in class to activate a carbonyl function is acetalisation. One of the steps involved is the following : So I was wondering, is that a $\ce{S_{N}1}$ or a $\ce{S_{N}2}$ ? ...
5
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1answer
222 views

Furan and maleic anhydride: Why is the major product exo?

For most Diels-Alder reactions, the product is endo because there are favorable interactions between the newly forming pi-bond and the electron withdrawing groups of the dienophile. Why is the ...
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1answer
35 views

Rate law of the iodine clock reaction

I am dealing with the iodine clock reaction, which has the half-reactions: $$\begin{align}&\ce{H_2O_2 (aq) + 2I^- (aq) \to I_2 (s) + 2 OH^- (aq)} & (\text{slow}) \\ &\ce{I_2 (s) + ...
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1answer
37 views

Variation of Arrhenius equation with concentration

In the Arrhenius equation do Arrhenius constant and activation energy depend on concentration ? (Their units do)
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1answer
36 views

Should binding constants be unitless when deriving fractional occupancy equations from reactions?

It is known that binding (aka association) constants are in fact unitless, as has been discussed here already. However, I'm not a chemist and am confused about when one should or should not use units ...
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7answers
789 views

Will heating diatomic oxygen enough break the O=O bonds?

The bond enthalpy associated with a O=O double bond is equal to 495kJ/mol. Does that mean that adding enough kinetic energy in the form of heat will eventually cause the bonds to break and create ...
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2answers
32 views

Question regarding 1st order kinetics

We know for a $1^{\text{st}}$ order reaction $ A \rightarrow B$, we write the rate law as: Rate = $k[A]^{1}$, and the integrated law for this is $ \ln (\frac{A}{A-x}) = kt$. So by studying this ...
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1answer
66 views

Magical reaction tanks

I would be interested to know people's opinion on the following matter. Background Often, when the far-from equilibrium behaviour of a chemical reaction system is analysed mathematically (in papers ...
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123 views

Relationship between magnitudes of forward and reverse kinetic rate constants

Consider the reversible unimolecular reaction: $A \overset{k_{1}}{\underset{k_{2}}{\rightleftharpoons}} B$ We know that the forward reaction is often considerably more thermodynamically favourable ...
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39 views

Global warming kinetics

A rule of thumb in chemistry is that a reaction doubles in rate for every $10^\circ C$ increase in temperature. Considering the impact of a $10^\circ C$ increase in global temperature, would the same ...
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886 views

Why does potassium react the most vigorously with water?

Link to exam Which metal reacts most vigorously with water? (A) Ca (B) K (C) Mg (D) Na The given answer is B and the reasoning is that is is the most electropositive since it the furthest ...
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1answer
38 views

Which Ion is most kinetically inert?

im currently self teaching myself some chemistry, the textbook I am using is around degree level. I have come across a question though that has really stumped me: Which ion is most kinetically inert? ...
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1answer
66 views

Multiplication of the reaction and Equilibrium constant

$$\begin{align}\ce{2A + 2B &-> 2C }\\ \ce{A + B &-> C}\end{align}$$ Why does the equilibrium constant change? And why the rate of the first reaction square the rate of the second? I ...
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1answer
168 views

Rate Constant Units and Eyring Equation

Rearranging the Eyring equation leads to the following: $$ ∆^\ddagger S^\circ = R \ln{\frac{k \times h}{{k_B}{T}}}+\frac{∆^\ddagger H^\circ}{T} $$ where k is the rate constant, h is the Planck ...
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1answer
47 views

Is the end of a cigarette on fire when lit?

Is the end of a cigarette on fire when it is lit? Or is it smoldering? Is there a chemical difference between the two?
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2answers
55 views

Simple Kinetics Clarification

I just wanted to check my understanding of this. Given the reaction, $$ (1) \; \ce{A->B} $$ the corresponding rate law is $ v=k[A] $ Also consider $$ (2) \; \ce{A <=> B} $$ with forward ...
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1answer
71 views

Deriving goldman equation

So I've been trying to follow the derivation of the Goldman-Hodgkin-Katz equation on Wikipedia (https://en.wikipedia.org/w/index.php?title=Goldman_equation ) - I can follow it through after it sets up ...
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1answer
53 views

Can an excessive reactant amount result in a longer reaction time?

I am performing an experiment with DTZA and Ferrate. After a point of increasing the DTZA concentration too much the Ferrate takes longer (lower reaction rate) to react with the DTZA. Is this ...
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1answer
53 views

Why can't the molecularity be determined from the rate law?

Basically can someone explain why the molecularity cannot be determined from the rate law?
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44 views

The effect of concentration on the rate of a homogenous reaction

I have to do an experiment where I will find out what the influence of the concentration on the reactionspeed of a homogenous reaction is. We are asked to create 2 solutions, respectively A and B: ...
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1answer
51 views

Decreasing rate of reaction between $\ce{I2(s)}$ and $\ce{H2(g)}$?

Which change will decrease the rate of the reaction between $\ce{I2(s)}$ and $\ce{H2(g)}$? (A) Increasing the partial pressure of $\ce{H2(g)}$ (B) Adding the $\ce{I2(s)}$ as one piece ...
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1answer
115 views

Rate and order confusion

I just learned about rate and order... I just want to confirm if these three ideas are correct: If the first elementary step is the slow step, will the stoichiometric coefficients of the reactants ...
2
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1answer
153 views

Changes in which factors affect both the rate and the rate constant of a first order reaction?

Changes in which factors affect both the rate and the rate constant of a first order reaction? I. temperature II. concentration (A) I only (B) II only (C) Both I and II (D) ...
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2answers
366 views

What are some good examples of rate equations for a math class?

I'm a mathematician who's currently teaching a course on differential equations. Though I don't know much about chemistry, I like to include examples from chemistry in my course, and I prefer for the ...
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rate determination by 1H NMR spectroscopy

Currently I investigate a reaction where a starting material A reacts with an excess of thiophenol B towards products C and D. As shown by recurrent TLC analysis of the reaction, the formation of D ...
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1answer
29 views

Reaction Rate Limiting Reaction

Why exactly does the slowest reaction limit the instantaneous rate of a reaction even if the faster processes come after? Theoretically, if the products of the slow reaction are required for the fast ...
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2answers
44 views

Specific Case of the Rate law

My textbook says that for a chemical reaction with two reactants, $\ce{A}$ and $\ce{B}$ with equation $\ce{aA + bB -> Products}$, where $a$ and $b$ are coefficients, the general rate law is: ...
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Deriving the Rate Law

How do you derive the formula for the general rate law? Where does it come from, and why? I know how to use them and get information from them, but not why they are correct. Do they follow from the ...
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1answer
124 views

Reaction Order Greater than 1

What is the chemistry behind why reactions of order >1 exist? And what role does the number of activated complexes formed have in determining reaction rate?
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1answer
77 views

Temperature in the Maxwell-Boltzmann Distribution

I am attempting to generate the probability for the specific speed of a molecule using the Maxwell-Boltzmann distribution, but I cannot decide on which temperature I should use in the equation. For ...
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1answer
482 views

Calculate the specific rate constant (k)

The question is: Suppose we found that the reaction of Red#3 with bleach is 1st order in hypochlorite. The observed rate constant ($k_{obs}$) for one of the trials was measured to be $0.00400 ...
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550 views

Finding the average rate of consumption

The question is: If $2.0 \cdot 10^{-4}$ moles of dye in $50$ mL of solution is consumed in 188 seconds, what is the average rate of consumption of dye in $\text{mol}/\text{L}\cdot \text{s}$? I am not ...
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1answer
37 views

Evaporation velocity of ethanol: adding ethanol vapour to a gas mixture

I need to add a known amount of ethanol vapour to a gas mixture (He/Ar). To do that I let the mixture bubble in liquid ethanol kept at a known temperature (14 C). The system is made of a large steel ...