What is Reaction rate: Definition and 49 Discussions

The reaction rate or rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit time. Reaction rates can vary dramatically. For example, the oxidative rusting of iron under Earth's atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second. For most reactions, the rate decreases as the reaction proceeds. A reaction's rate can be determined by measuring the changes in concentration over time.
Chemical kinetics is the part of physical chemistry that concerns how rates of chemical reactions are measured and predicted, and how reaction-rate data can be use to deduce probable reaction mechanisms. The concepts of chemical kinetics are applied in many disciplines, such as chemical engineering, enzymology and environmental engineering.

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  1. 1

    MCNP6.2 - ENDF/B reaction numbers for tally multiplier

    Hi everyone, I am trying to evaluate the spectral index of an nonelastic (n,n') reaction. For that I want to set up a tally multiplier on a cell (let's call it cell 10). The reaction is present in the ENDF/B library as MT=4 but I have not seen it in the table of the special reaction numbers...
  2. samy4408

    Medical Hello, I found a weird sentence in a book about enzymes....

    Hello ! We all now that enzymes lower the activation energy by creating both covalent bonds and week non covalent bonds , in this book , about how the enzyme lower the activation energy using covalent bonds they said : this sentence is not compatible with a basic principle that i learned in...
  3. E

    Theoretical reaction rate for water electrolysis

    So I'm designing a proces where carbondioxide is converted into methane using the Sabatier reaction. For this reaction hydrogen is required which I'm planning on producing using the electrolysis of water. But I'm having a problem where I need the speed of this reaction to determine the size of...
  4. I

    Chemistry What is the relationship between temperature and reaction rate?

    I think I should use ln(K2/K1)=Ea/R(1/T1 - 1/T2), and find K2/K1. I am given T1 and T2, but not Ea. I'm not sure how to continue. Thanks. (note: the answer is C)
  5. R

    MATLAB Plotting Reaction Rate vs Temperature with MATLAB

    I know how to get fusion cross section plots from the exfor website but now I need to plot the reaction rate as a function of temperature. According to the image, I have sigma and E values as x and y data. How do I integrate using MATLAB .
  6. Sabra_a

    Reaction rate, rate equation and half life

    Summary: Hydrogen peroxide, H2O2, decomposes as per following reaction scheme: H2O2(l) → H2O(l) + O2(g) The concentration versus time data for the decomposition of hydrogen peroxide is given in Table 1. i) Calculate the reaction rate constant, k, graphically, with the aid of Excel software...
  7. I

    Nuclear reactions, cross section, reaction rate

    Homework Statement A beam of ##^{50}##Ti nuclei impinged on a ##0.5 mg/cm^2## thick ##^{208}##Pb target in an experiment lasting 176 hours. During that time a total of ##3260 \; ^{257}##Rf nuclei were detected. The beam intensity was throughout the experiment constant at ##6.6\mu A##. Each...
  8. Nguyen Ngoc Anh

    I Reaction Rate: Calculations & Limitations

    Dear all, As we know, the reaction rate can be calculated as following: R = N * σ * Φ (1) Where R is reaction rate (events/s/cm3) σ is cross section (cm2) Φ is flux of incident particle beam (particles/s/cm2 N is density of target (atoms/cm3) Logically, there is a limitation of R, because...
  9. kiwaho

    I How many barns above could make nuclear reaction rate 100%?

    All guys know the importance of cross section. In a sense, it stands for the possibility of a reaction. I am wondering how many barns above could make nuclear reaction rate almost 100%? Generally speaking, the cross section can span a couple of decades order of magnitude, e.g. 10^-10 to 10^6...
  10. ShellDough

    Question regarding the rate law of a reaction

    Homework Statement Data in the table were collected at 300 K for the following reaction: A(g) + B(g) → products Concentration of A 1.00 0.100 1.100 Concentration of B 0.100 0.100 1.00 Initial Rate (M/s) 1.29x10^-29 1.33x10^-30 1.30x10^-29...
  11. N

    Calculating N2O4 Reaction Rate in 4L Container

    Homework Statement N2O4 --------------> NO2 N2O4 for k = 0.050 s-1 The process starts from 0.20 mole of N2O4 in a container of 4.0L. Calculate v for N2O4. if 3/4 of the N2O4 is converted Homework Equations To calculate concentration c= mole/L The Attempt at a Solution 0.20 mole /4.0 L...
  12. T

    Catalyst increasing both forward and reverse reaction rate

    The question is: Which takes place when a catalyst is added to a reaction at equilibrium? A. The point of equilibrium is shifted to the right. B. The point of equilibrium is shifted to the left. C. The forward and reverse reactions rates are increased unequally. D. The forward and reverse...
  13. Marie Cailey

    Experiment for testing type of catalyst on reaction rate?

    < Mentor Note -- thread moved to HH from the technical forums, so no HH Template is shown > experiment for testing type of catalyst on reaction rate? I need an experiment (just the method) Where I can test the reaction rate of changing the catalyst type I need about 3 differnet catalysts e.g...
  14. MexChemE

    Mass balance with reaction -- Chemical kinetics POV

    Good evening, people of PF. Recently, while studying chemical kinetics, I have come across some questions about reaction rates and rate equations. I've noticed some inconsistencies between the chemical kinetics point of view, and the approach taken by chemical reaction engineering and reactor...
  15. U

    What is the expected rate of reactions in the detector?

    Homework Statement A reactor fires out ##10^{21}## neutrinos per second. A detector containing ##10m^3## of liquid which contains 30 carbon atoms every 60 hydrogen atoms. The detector-reactor distance is ##1000##. The cross section for the reaction is ##\sigma = 10^{-46} m^2##, and the density...
  16. W

    Gamow peak and nuclear reaction rate

    It's known that the nuclear reaction rate (inside a Star) can be determined with $$R_{ab}=n_a n_b\left<\sigma v\right> \, \approx \, n_a n_b \Big(\frac{8}{\pi m_e}\Big)^{1/2} \frac{S(E_0)}{(k_BT)^{3/2}} \Delta \frac{\sqrt{\pi}}{2} e^{-3E_0/k_BT},$$ where ##k_B## is Boltzmann constant, ##T##...
  17. A

    How does pressure affect the rate of a gaseous reaction?

    The question is: The rate equation for the reaction A2 + B2 -> 2C (all gases) is rate = k[A2]2[B2]. If the gaseous reaction misture is compressed to half its original volume, by what factor will the reaction rate change. Assume temperature is constant. My thoughts are that the reaction rate...
  18. Entanglement

    Law of Mass Action vs The Reaction Rate Law

    Why in the Law of Mass Action we raise the concentrations of the reactants to the power of their coefficients according to the stoichiometry of the chemical reaction, while the order of the reaction must be determined experimentally ? I may not understand the difference between them.
  19. C

    Surface area contact with catalyst effect on hydrogen redox

    I have also posted this question here: Relationship between surface area of electrode and reaction rate of hydrogen in fuel cells, but I really need an answer before tomorrow morning so I hope you don't mind me posting it here as well! I am looking at the effects of increasing the surface area...
  20. Chemer

    Rate of Reaction: Exploring Chemical Kinetics

    Hi, Can anyone explain me that in chemical kinetics, the rate of reaction can be determined by just determining the rate of any reactant of product involved in the reaction, but how? How the rate of change of concentration of just one specie can tell you about the whole reaction? I found the...
  21. gfd43tg

    Proposing a reaction rate mechanism

    Homework Statement The rate law for the reaction is found from experiment to be Suggest a mechanism consistent with the rate law. Homework EquationsThe Attempt at a Solution Here is the webpage with the solution http://www.umich.edu/~elements/07chap/frames.htm Here is the solution Rate...
  22. gfd43tg

    PFR Reaction Rate: Understanding CSTR vs. PFR

    Hello, In class, my professor said that in a CSTR, the reaction rate is constant throughout a well mixed CSTR. He said in most cases, a PFR will react faster than a CSTR. I can see how the PFR will have a fast reaction rate at the entrance to the tube, and slowest at the exit. However, what...
  23. gfd43tg

    Change in concentration vs. reaction rate

    Hello, I am wondering, why is it that ##\frac {d[C]}{dt} \ne k[C]## in general, where ##C## is a chemical species, and the product ##k[C]## is the reaction rate, ##r##. ##r_{c} = k[C]## My thoughts is that because the units aren't necessarily the same, therefore they can't be the same. But I...
  24. S

    Reaction rate from added vibrational energy

    I have a molecule with a certain kinetic, vibrational, and rotational energy. It absorbs a photon which excites a vibrational mode. I want to find an equation that describes how the molecules reaction rate with another molecule might change given the added vibrational energy. Is there a name...
  25. S

    How to increase reaction rate using EM radiation?

    I want to pump energy into a chemical species to increase its reaction cross section with another. Typically these species react upon collision when their relative kinetic energy exceeds the activation energy. I want to find a way to increase the reaction rate for interactions at slower...
  26. M

    Reaction rate for multiple steps

    Just a curious question. How would the rate for a net reaction involving multiple steps of all similar (perhaps exact - i know it's highly unlikely) activation energies be calculated? I've been told to just look at the slowest step (highest EA) in all cases, even if they are similar in...
  27. T

    Rate of Ammonia Prod. in N2+3H2 Reaction

    Homework Statement This is not a homework question, rather, I am just trying to clarify a concept and example in my textbook. Ammonia is produced by the reaction of Nitrogen (N2) with hydrogen (H2) as shown in this equation. N2 + 3 H2 --> 2 NH3 The rate of ammonia production is 5.0 x 10-6...
  28. D

    Transmission coefficient in reaction rate theory

    This question relates to rate constants of transition events. The transmission coefficient κ reduces the value of the rate constant compared to the transition state theory (TST) value. I understand κ to be defined as the probability that a reaction coordinate q will proceed to product given that...
  29. K

    Difference between Reaction Rate and Rate Law?

    Lets say you have the reaction aA + bB => cC + dD The rate of the reaction is given by the change in initial concentration over the change in time. -\frac{\Delta \left[ A \right]}{a\Delta T}\; =\; -\frac{\Delta \left[ B \right]}{b\Delta T}\; =\; \frac{\Delta \left[ \mbox{C} \right]}{c\Delta...
  30. Mandelbroth

    [Chem] Reaction Rate (Differential Equations)

    I'm only in a high school class. I just made up this problem to see if I'm getting the right idea in the long run. That, and then there's the fact that differential equations are SO MUCH FUN! :biggrin: Homework Statement Molecular bromine (initial concentration: 0.49 M) and formic acid (initial...
  31. A

    [Chem] Problem finding a source for reaction rate constant

    Homework Statement I had an assignment where I needed to calculate reaction rate constants at different temperatures. I was supposed to use ab initio method (meaning I should use Spartan software), molecular partition functions and Eyring equation. The reaction was: H+HD...
  32. K

    Reaction Rate of a Solar Fusion

    Homework Statement Find the reaction rate of a star purely of Hydrogen at temperature of 15MK, density of 150gm/cm^3, most of the reactions take place at R0=0.25R. Each reaction released energy of 25MeV Homework Equations This is the part I'm lacking. I've got the number of protons...
  33. C

    Alka-Seltzer + Soap reaction rate

    Hello, I have seen that adding dish soap to water and then dissolving Alka-Seltzer in the solution causes the reaction rate to slow. Does anybody have any idea as to why this happens?
  34. C

    Chemical kinetics - reaction rate

    Homework Statement 2HCl + Na2S2O3 -> 2NaCl +S + SO2 + H2O Find the order of reaction with respect to S2O32- and H+ volume of 3.0M HCl was held constant at 2ml Homework Equations S2O32- + 2H+ -> S + SO2 + H2O rate = k[Na2S2O3]m[HCl]n (see number 3.) The Attempt at a Solution i just...
  35. N

    Why doesn't inert gas affect reaction rate?

    Just as the title says, I'm having difficulty understanding why the concentration of inert gas is not included in the reaction rate. I would think adding a higher concentration of N2 (or some other inert gas) would increase the reaction rate. Perhaps, I'm confusing reaction rate with space time?
  36. B

    Three species reversible reaction rate

    The problem statement says to derive the concentration as a function of time for the general three species first order reactions. I have attached an image of the problem, so see the image for the reaction. I have written the reaction rates for all the reactions but I am having trouble...
  37. C

    Reaction Rate of NO & O2 to Form NO2

    Homework Statement The reaction rate of nitrogen monoxide and oxygen into nitrogen dioxide is given by the expression r = k [NO]2 [O2], where r = reaction rate k = reaction rate coefficient, which increases with increasing temperature. Homework Equations What is the increase in the...
  38. C

    Calculating Reaction Rate Increase with a Temp. Rise of 10degC

    Homework Statement By what factor would the rate of a reaction for which the activation energy is 159 kJ be increased by a temperature rise of 10degreesC from 25 to 35degreesC? Homework Equations The Attempt at a Solution
  39. U

    Reaction Rate Order for High Temperature Gas-Solid Reactions

    Hello chemists! In the classical treatment of reaction kinetics, the overall reaction rate is usually written as a constant times the concentration of species raised to some power (called the order of reaction for that species). It is impressed in high school level students that this reaction...
  40. A

    Webpage title: What are the Rate Equations for a Parallel Reversible Reaction?

    I know the rate equations for a parallel reaction are d[A]/dt =-k1[A]-k2[A] d[B]/dt =k1[A] d[C]/dt =k2[A] and I know that the rate equations for a reversible reaction are d[A1]/dt =-k1[A1]+k2[A2] d[A2]/dt =k1[A1]-k2[A2]-k3[A2]+k4[A3] d[A3]/dt =k3[A2]-k4[A3] But what would d[A]/dt...
  41. S

    Question about the concept of Reaction Rate

    This is not a homework question. Im curious as to why in some situations rate is described as s^{-1} without a change in property in the numerator. As i understand, rate is defined as a change of a property over the time elapsed over that change.. How can we have a reaction rate without...
  42. F

    Reaction Rate Experiment - Concentration

    Solution A: is a dilute soultion of potassium iodate, KIO3 which is the source of iodate, IO2(1-) Solution B: contains some starch and the other reacting species, the hydrogen sulfite ion, HSO3(1-) 1. In a small beaker obtain about 50mL of solution A (0.02 M IO3(-)) and in another small...
  43. L

    Mathematical relationship between reaction time and reaction rate HELP

    Homework Statement I am writing a report for an Iodine clock lab, the questions I am having trouble with are: 1.What mathematical relationship exists between reaction rate and reaction time? 2.What mathematical relationship exists between concentration and reaction time? 3.What mathematical...
  44. G

    Chemistry; reaction rate - completion

    Chemistry; reaction rate -- completion Homework Statement A first-order reaction is 17% complete after 30 min. How long after the start of the reaction will the reaction be 80% complete? Homework Equations ln[A] = ln[A0] - kt The Attempt at a Solution [A] = 0.83 [Ao] = 1.0 t...
  45. P

    Reaction rate mol-1sec-1 to sec-1

    Homework Statement Hi there. I have a reaction A + B = C I am told the reaction rate is 0.8/mol.min and I know how many molecules of A and B I have. So my question is how do I get to the reacting rate in units of time only? The second part of the question is the same but for a...
  46. A

    Help: Zn and HCI reaction rate.

    I need to check at what rate Zn and HCl react to release hydrogen gas. How do I construct a hypothesis? What method should I use? What would the variables be? (independent, dependent, and controlled) What relevance would all of this have to society? Please help...
  47. L

    Reaction of I- & H2O2: Rate of H2 Appearance

    Question The rate of appearance of I2 in aqueous solution, in the reaction of the I- ion with hydrogen peroxide, was found to change from 3.7*10^-5 mol/dm^3 to 7.9*10^-5 mol/dm^3 over a time interval of 1.0 to 3.0s. 2H+(aq) + 2I-(aq) + H2O2(aq) --> I2(aq) + 2H2O(l) a)What is the rate of...
  48. S

    Reaction Rate and Activation Energy

    1) Methanol can be produced by the following reaction: CO (g) + 2H2 (g) --> CH30H (g) How is the rate of disappearance of hydrogen gas related to the rate of appearance of methanol? -delta[H2]/delta t = ? a. + delta [H2]/delta t b. + 1delta[CH3OH]/2delta t c. + 2 delta...
  49. C

    How Do You Calculate the Production Rates of P4 and H2 in a Chemical Reaction?

    Could someone could help me with this reaction rate problem? 4PH3(g) ------- P4(g) + 6H2(g) If, in a certain experiment, over a specific time period, 0.0048 mol PH3 is consumed in a 2.0 L container each second of reaction, what are the rates of production of P4 and H2 in this experiment. I'm...