Chemistry Stack Exchange
Chemistry Stack Exchange

Questions tagged [kinetics]

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

Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states, as well as the construction of mathematical models that can describe the characteristics of a chemical reaction.

In elementary physical chemistry, the study of chemical kinetics involves studying a few "orders" of kinetics (zero, first, second, pseudo-order); their half-lives; concentration or log[concentration] vs. time graphs; Radioactive decay and growth kinetics are also frequently covered.

1152 questions
26
votes
2 answers

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 details to be accurate. Here is a typical exam…
Jim Belk
  • 363
  • 2
  • 7
25
votes
3 answers

How to identify zero order reactions?

I have come across many reactions that are zero order reactions but at one glance I'm unable to tell if they are zero order or not. Is there any criteria that can be used to identify these reactions or are they purely experimentally determined?
Ashu
  • 1,453
  • 12
  • 22
16
votes
3 answers

Is the rate determining step the step with the largest Ea?

I've seen some controversy on this question while doing a brief search. For example, this SE answer quotes Wikipedia and says that the RDS is the step with the largest $E_a$. However, this UC Davis page says that In the potential energy profile,…
carbenoid
  • 2,032
  • 6
  • 23
  • 42
14
votes
1 answer

Is the Arrhenius Equation only valid for reactants in the gas state?

I couldn't find a source that explicitly say this, but given the gas constant R is used, is the Arrhenius equation only valid when all reactants are gases? Do they have to be ideal gases? If the above is true, is there a similar equation for…
Yandle
  • 901
  • 10
  • 19
11
votes
3 answers

Does a reaction have to have a rate determining step?

I am a bit confused about the concept of the rate determining step. From what I understand, a step in a reaction is the RDS if it meets the following requirements: It is the slowest step in a reaction It causes a bottleneck in the progress of the…
guogogo
  • 405
  • 2
  • 5
  • 11
10
votes
2 answers

Is negative activation energy possible?

Is negative activation possible? And, in coupled reactions is there any difference? Because I saw in the paper - Chemical Engineering Science 1996, 51 (11), 2995–2999 - the following conclusion: Negative activation energies of reaction have been…
Chrysi
  • 101
  • 1
  • 4
10
votes
1 answer

Unit consistency in rate equations

I suppose that my problem is not one of great profundity, but it is an annoying one. The problem is related to the measurement units involved in rate equations of different order. Not being a chemist myself, I have in my work encountered equations…
Kalle
  • 101
  • 3
9
votes
2 answers

How does initial rate of reaction imply rate of reaction at any time?

My textbook begins the Chemical Kinetics section by describing the "Initial Rates Method" of determining the rate of reaction. I understood it as the following (for a first order reaction): $$\ce{A ->…
Greg
  • 1,191
  • 3
  • 11
  • 15
9
votes
1 answer

If the rate law order is three, does that mean that three bodies collide at some elementary step?

I am doing a chemistry review about rates, and I get asked "Which of these statements is false?" The answer is In reactions that are second order in one reactant and first order in another, the slow step generally involves a three-body collision…
Blubber
  • 275
  • 1
  • 2
  • 7
8
votes
1 answer

How to identify if a chemical equation has a 'fractional order'?

Consider the following reaction: $$\ce{CHCl3 + Cl2 -> CCl4 + HCl}$$ The rate law expression is: $$\text{Rate} = [\ce{CHCl3}]\cdot[\ce{Cl2}]^\frac{1}{2}$$ with an order of $1.5$. But 'how can we determine' this fact? And why is it $1.5$ and not $2$?
deKRYPTONator
  • 189
  • 5
7
votes
2 answers

Why does a reaction take time?

A reaction in nature is, as we know, generally an interaction between the electron clouds of different atoms and nuclei. Why does this takes time?
BIMAN BASU
  • 87
  • 1
7
votes
2 answers

How to derive the rate laws for three consecutive reactions?

Given the following three consecutive unimolecular reactions $$\ce{A ->[$k_1$] I_1 ->[$k_2$] I_2 ->[$k_3$] P}$$ write the rate of change for each. I have gotten the following:$\newcommand{\diff}{\mathrm{d}}$ \begin{align} \frac{\diff [A]}{\diff…
MathCurious314
  • 392
  • 2
  • 7
7
votes
2 answers

Does stoichiometry matter in extent of reaction calculation?

I was recently introduced to the extent of reaction and learned that it can be calculated using this equation $$\xi = \frac{n_{A,out}-n_{A,in}}{\nu_A}.$$ If I'm using this formula to calculate the extent of reaction, does it then depend on how I…
Leon
  • 83
  • 2
6
votes
1 answer

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 confusion with. Task 8. Decomposition of Nitrous…
Tan Yong Boon
  • 10,415
  • 4
  • 42
  • 108
6
votes
2 answers

Second order reaction with two reactants

I'm interested in the second order reaction $\ce{A + B -> P}$. Mass action kinetics is assumed. Let $[A]_0 = a$ and $[B]_0 = b$, then $[A] = a - x$ and $[B] = b - x$. The rate law becomes $$-\frac{\mathrm dx}{\mathrm dt} = -k([A]_0 - x)([B]_0 -…
AGR
  • 69
  • 1
  • 4
1
2 3
…
11 12