Questions tagged [kinetics]

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

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Do coefficients matter in rate law?

For reaction $\ce{2A→B}$ (elementary step), according to the rate law, rate $= k [A]^2$. In some calculations, we use $k[A]^2$ as the production rate of B. Why isn't it ${1 \over 2} k[A]^2$? In this ...
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Is there a general consensus on the causes of the alpha-effect?

There have been various explanations posited for the α-effect. The α-effect refers to a phenomenon wherein nucleophiles with lone pairs on atoms adjacent (i.e., in the α- position) to the atom bearing ...
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Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

Take for instance the reaction $$\ce{H2(g) + I2(s) <=> 2HI(g)}$$ The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a ...
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Relation between chemical kinetics and chemical equilibrium

In my chemistry book, the law of chemical equilibrium is derived from the law of mass action: For a reversible chemical reaction $$\ce{aA +bB\rightleftharpoons cC + dD}$$ where $a$, $b$, $c$ and $d$ ...
2k 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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How is it that the equilibrium constant does not depend on the mechanism?

For a reaction of the form $$\ce{aA + bB <=> cC + dD}$$ the equilibrium constant is $$K_c=\frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{A}]^a[\ce{B}]^b}$$ regardless of the mechanism of the reaction. ...
132k views

Difference between thermodynamic and kinetic stability

What is the difference between thermodynamic and kinetic stability? I'd like a basic explanation, but not too simple. For example, methane does not burn until lit -- why?
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Can in any case the faster step of the reaction be rate determining?

I found a sentence in book which states the reverse step of this reaction ( I forgot what was it!) has the faster step as rate determining . Even Rate determining step-Wikipedia states: In ...
21k views

Is activation energy temperature-independent?

I know that activation energy for a reaction is the extra energy given to the reactants to reach the threshold energy so that they can collide and react. But then, why is it said that the activation ...
6k views

Rate Constant Units and Eyring Equation

Rearranging the Eyring equation leads to the following: $$\Delta^\ddagger S^\circ = R \ln{\frac{k \times h}{{k_\text{B}}{T}}}+\frac{\Delta^\ddagger H^\circ}{T}$$ where $k$ is the rate constant, $h$ ...
3k views

Are there any reactions with no activation energies?

Are there any reactions with no activation energies? Our professor just told us there are no chemical cliffs. Is this true? I read something about nuclear decay as being a reaction with no ...
520 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 ...
7k views

How to relate a reaction barrier to the time the reaction needs to proceed?

As I am writing this I am at a conference and one of the participants just asked a question where he linked reaction barriers to durations for the reaction to complete. To paraphrase: From our ...
418 views

Is it possible to make an anticatalyst?

I'm wondering if it is possible, theoretically, to create compounds which perform the opposite function of a catalyst (thus an anticatalyst). That is to say, could a compound be made which raises the ...
754 views

Belousov-Zhabotinsky reaction: questions about rate determining step, k and activation energy

In one of our lab courses, we performed a variation of the BZ reaction, the experimental procedure is outlined below: Experimental Procedure 10 mL of 3.0 M $\ce{H2SO4}$ was added to test tube T1. ...
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Why is proton transfer so fast?

Why is proton transfer always kinetically favored? In other words, why are Brønsted acid-base reactions so quick? Is it because protons are generally unhindered, sterically? This seems plausible; ...
17k views

Is there a difference between equilibrium and steady state?

The term equilibrium is used in the context of reversible reactions that reach a point where concentrations no longer change. The term steady-state is used in enzyme kinetics when the concentration of ...
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Equilibrium constant for heterogeneous equilibria having aqueous as well as gaseous reactants

Suppose we have a heterogenous equilibrium : $$\ce{A(aq) +B(aq) <=> C(g) +D(aq)}$$ Which equilibrium constant is used here? Both pressure and concentration terms are there. So, according to me, ...
253 views

Which rate, the forward or reverse rate of acid dissociation, is more strongly affected when diluting acetic acid in aqueous solution?

Acetic acid is a weak acid. It is in equilibrium with acetate and hydronium ions in aqueous solution: $$\ce{CH3COOH(aq) + H2O(l) <=> CH3COO-(aq) + H3O+(aq)}$$ Ostwald's law states that the ...
397 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 ...
8k views

How can a catalyst not be included in a rate equation if, by definition, it speeds up a chemical reaction?

I thought that anything not in a rate equation was automatically zeroth order and therefore did not affect the reaction. However, I have heard that catalysts can be involved in a reaction while not ...
682 views

Representing woody biomass concentration for kinetic reactions

Woody biomass is composed of cellulose, hemicellulose, and lignin components. The following diagram provides representative formulas for each component: Biomass can be represented by it's density, ...
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Half-life equation for 2nd order kinetics

My friends and I were doing some problems from this year's IChO Preparatory Problems (PDF from the 49th International Chemistry Olympiad (2017)) when we stumbled upon a question which we had some ...
784 views

Is the kinetic energy turning into activation energy when the reaction takes place? [closed]

So I want maybe a simple question that I had on a test today. For a reaction to take place it needs a minimum energy called activation energy. At school I heard that this energy is coming from the ...
417 views

Conservation equation in an enzyme-catalysed reaction

Consider the reaction scheme: $$\ce{S + E ->[k_1] C1} \qquad \ce{C1 ->[k_2] E + P} \qquad \ce{S + C1 <=>[k_3][k_4] C2}$$ where $\ce{S}$ is the substrate, $\ce{E}$ is the enzyme, $\ce{P}$ ...
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SN1 vs SN2 in low concentration of nucleophile

Why is SN1 mechanism favoured by low concentration of nucleophilic reagent? It is a first order reaction so shouldn't the reagent be in excess? Also higher the concentration of reagent faster the ...
Consider the hypothetical reaction described by the following equation: $$\ce{3 A + 2 B -> C}$$ Reagent B was added in excess and the following time concentration data was obtained. \begin{array}...