What is Reaction: Definition and 1000 Discussions

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, and sometimes intermediate products and reaction conditions.
Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration. Typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms.
Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium. Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of free energy to go forward (examples include charging a battery by applying an external electrical power source, or photosynthesis driven by absorption of electromagnetic radiation in the form of sunlight).
A reaction may be classified as redox in which oxidation and reduction occur or nonredox in which there is no oxidation and reduction occurring. Most simple redox reactions may be classified as combination, decomposition, or single displacement reactions.
Different chemical reactions are used during chemical synthesis in order to obtain a desired product. In biochemistry, a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form metabolic pathways. These reactions are often catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperatures and concentrations present within a cell.
The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays, and reactions between elementary particles, as described by quantum field theory.

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  1. S

    Mechanical guy needs help with endothermic reaction and heat decomposition

    How did you find PF?: Google I am working on a project that requires us to protect components from high heat. We were thinking on using sodium bicarbonate, but our module needs to be exposed FIRST to 85C for long periods.... then the high heat exposure will be present. We believe this...
  2. eneacasucci

    B Conservation of charge in a nuclear reaction

    Conservation of charge: The sum of the charges on all the particles before and after a reaction are the same I was considering this reaction: n + 3 He → 3 H + p + 0,764 MeV Making the charge balance I have: 0 + 0 (2protons + 2 electrons) → 0 (1proton + 1electron) + 1 (proton) There is...
  3. Grandpa04

    Static Equilibrium Reaction Question about Fixed Point

    For this problem I set ΣFy = -3kN - 0.75kN - 3kN + Ay + By (with By representing the right side vertical force, and Ay representing the left side force). For ΣM, I used the rectangular distributed load of 0.5 kN at 3m from point A as the pivot: ΣM = -3m*Ay - (0.5kN*4m) - 3kN*6m - 5kN*m + By*6m...
  4. Greg Bernhardt

    Announcement Small PF update this weekend

    We'll be updating PF software this coming weekend. Hoping to fix some pesky bugs! Shouldn't be down for more than 15-20min. Likely Saturday morning.
  5. T

    Need Recommendations for Nuclear Reaction Modelling Software

    Working on a project where I need to model nuclear reactions with different fuel pellet shapes. Does anyone have recommendations for software that's good for this? Any advice or experiences are also welcome!
  6. yucheng

    Reaction between hydrogen halide and sulfuric acid

    I am studying the reaction $$\ce{NaX(s) + H2SO4(conc.) -> NaHSO4 + HX \uparrow} \tag{1}$$ with the conditions similar to this video below Solid halides with concentrated sulfuric acid What reaction is this? Precipitation reaction? In other words, will sodium bisulfate be precipitated? I...
  7. J

    Fuel Cell Reaction Question - is this right?

    The quantity (dE_dP)_T can be derived using the Gibbs-Helmholtz equation which states that dE = TdS - PdV + μdN where E is the internal energy of the system, S is the entropy, V is the volume, N is the number of particles and μ is the chemical potential. Differentiating this equation with...
  8. aquastor

    Determine the signs of ∆H, ∆G, ∆S for the reaction: N2(g) → 2N(g)

    Hello are you able to explain the two incorrect ones. I am not sure how to do this as there is no phase change involved, nor is there a temperature or volume change.
  9. lk0306

    Do these substances emit formaldehyde gas when heated?

    Hey there, Trying to confirm whether or not these substances emit formaldehyde gas when subject to heat of hair straightener and hairdryers. Both were ingredients in a keratin treatment i used at home and i had a crazy reaction (irritated skin, eyes, hair, nose and lungs) in the process of...
  10. K

    How Do You Calculate m3 and m4 in Nuclear Reaction Equations?

    En=0 Ek(B)=0 Q=Ek3(α)+Ek4(Li) --Q=Ek3(1+m3/m4) (1) p3=p4 /^2 -- 2*m3*Ek3=2*m4*Ek4 --- Ek4=m3/m4 * Ek3 (2) (1) and (2) Ek4= m3/(m3+m4) * Q, but I'm not sure how to find m3 or m4 and if this is true
  11. T

    I Pickleball Physics -- Player reaction time vs aging

    Out of curiosity, how fast are the hands of the pros? I have timed an exchange between BJ/ALW and JD/JI that occurred at the Baird PPA in September 2022. The ball made the (about) 14 foot trip 11 times over 4.0 seconds, for an average trip time of 363mS (milliseconds). (Average speed of 26.3...
  12. H

    A Radiation back reaction in classical electrodynamics

    I've been doing some research on the topic of radiation reaction force/self force in classical electrodynamics and although there are some discussions on the internet I would like direct answers to these following questions: Is there a rigorous and universally accepted treatment of radiation...
  13. N

    Feynman diagram for ##\mu^+\mu^-## production in ##p\bar{p}## reaction

    I was able to solve b) but I am confused for a). I understand that in the proton-antiproton collision, only two quarks (one from proton and other from anti-proton) can be combined to get a virtual photon that in turn creates muon and anti-muon. I don't understand what would happen to the other...
  14. J

    I Reaction moment on I.C. engine when we increase RPM

    Every time when you increase RPM on longitudinal placed internal combustion engine, car shake to side in oposite direction of crankshaft rotation. This is reaction moment for change in RPM of crankshaft/flywheel. How this reaction moment transfer to engine block/car if crankshaft is separated...
  15. V

    Heat Radiation question (skin's reaction to UV versus IR radiation)

    I am not sure of the answer. But I am guessing that infra-red rays carry more heat radiation than ultra-violet rays, and the heat is instantly felt on our skin when exposed to both these rays. So what we feel is the heat sensation from infra-red rays and that sensation is missing when it's...
  16. P

    Does the term ##ln(k)## have units in reaction based equations?

    $$ln{x/t}=lnk +aln[S_2O^{2-}_8] $$ From the above equation,I made a table with the experimental data of the two terms ##ln{x/t}## and ##ln[S_2O^{2-}_8] ##Bur I didn't mention units for them as I had known that even if k had unit,##lnk ## wouldn't have had.But my teacher pointed out...
  17. Z

    Elbow Flexion Joint Reaction Force

    Homework Statement:: This is not a homework, but I want to know how to find the joint reaction force of the 2d elbow flexion, if I know the angular acceleration of the forearm, and the mass of elbow with a known weight on hand. I assume the forearm is a simple cylinder. Suppose the angular...
  18. G

    Reactions at the beam supports

    Figure: My attempt at a solution: We know that ##Q=A_T## We calculate ##Q##: $$Q=\dfrac{3\cdot 480}{2}+\dfrac{600\cdot 6}{2}+600\cdot 2=3720\, \textrm{lb}$$ Then we look for the point ##\overline{x}## of the centre of gravity: $$\overline{x_1}=1\, \textrm{ft},\quad...
  19. F

    I Reaction force of and its relation to normal force and friction

    Hello, When we consider a block sitting on a surface, the gravitational force ##W## and the normal force ##F_N## are applied to the block. Both equal i magnitude and opposite in direction. We call the normal force the reaction force exerted by the surface on the block. Now we consider the...
  20. J

    Why would a reaction be nonspontaneous at higher temperatures?

    Using the gibbs free energy equation ## \Delta G = \Delta H - T \Delta S ##, If I have a reaction where ##\Delta H## is negative (exothermic?) and ## \Delta S## is negative it makes ##\Delta G## positive at higher temperatures which means the reaction is nonspontaneous at higher temperatures...
  21. T

    Chemistry How can ideal gases be used to determine the change in enthalpy using Hess' law?

    I feel that the answer is B) because Increasing the pressure increases the intermolecular forces Of the gas molecules but I do not see how this In effect will lead to an increase in the enthalpy
  22. hilbert2

    Medical Nootropics that improve motor reaction time

    Spearmint extract and lemon balm have an effect of making you faster in ball games and martial arts, not only improving mental cognition. https://www.nutritionaloutlook.com/view/nootropic-spearmint-extract-may-improve-reactive-agility-according-new-study The active compound in it seems to be...
  23. gggnano

    Is it possible to have an "Eternal reaction" by mixing the products?

    So this is a very simple concept but I am not explaining it well: Let's say you have 4 reactants in 2 different reactions (apologies: the symbols I am using do NOT exist, other than the "C" symbol, I just can't find real elements so that I am using just alphabet symbols as an allegory to show...
  24. S

    Calculating Energy Released in a Fission Reaction: Where Did I Go Wrong?

    Energy = ##\frac{2000}{235}## x 6.02 x 1023 x 0.7% x 200 x 1 x 106 x 1.6 x 10-19 = 1.15 x 1012 J But the answer is 1.15 x 109 J I am off by a factor of 1000. Where is my mistake? Thanks
  25. K

    I 7Li(p,e+e−)8Be direct proton-capture reaction X17

    What is the significance of 7Li(p,e+e−)8Be direct proton-capture reaction ? there are these papers, Slope of the astrophysical S factor for the 7Li(p,γ)8Be reaction January 2000 https://www.researchgate.net/journal/Physical-Review-C-1089-490X 61(1):15802- DOI:10.1103/PhysRevC.61.015802 The...
  26. V

    How can the force of a normal reaction be electromagnetic?

    I do understand that gravitational the electromagnetic force between two electrons or protons is very large compared to the gravitational force between them. I can see this by looking at the equation of gravitational force (##F= \frac {Gm_1m_2} {r^2}##) and the equation of electrical force given...
  27. Element13

    My Reaction to Mentor Bios/Interviews: WOW!

    Okay, so I just read a couple of the Mentor Bios/Interviews and I feel like a preschooler who just happened to crawl into a PhD symposium. To say that I'm completely, way-out of my league here doesn't even begin to come close to an understatement, I actually don't think that such a word even...
  28. A

    How can vinegar attenuate the pain of a bee sting? (acid base reaction)

    Hello, I have been working on this subject but I am not sure how to deal with it. I am looking to prove how can vinegar attenuate the pain of a bee sting. I have chosen a specific vinegar that is of 6° and 50 ml and Know the molecular weight of acetic acid is 60g/mol. The bee sting contains...
  29. Rub3y

    Do oxides react react with a weak acid like phosphoric acid?

    I have an ash which is a mix of oxides (Cr2O3, CuO, ZnO, PbO, CdO, NiO, SiO2, MgO, CaO). I am adding phosphoric acid. But as a weak acid, will it react with oxides? If so, are these conversions 100% or more of a equillibrium (partial conversion). I you need more information, be sure to ask.
  30. Rub3y

    How do I find conversions for a reaction with phosphoric acid?

    I have a solid ash mix containing oxides(ZnO, NiO, MgO, Cr2O3, etc.) and salts (Na2SO4, K2SO4, apatite, etc.). I am supposed to write all of the reactions with phosphoric acid (should be between 1 and 2 mol/l) and put it in a simulation for mass and energy balances. But since phosphoric acid is...
  31. Leo Liu

    How does D-T fusion reaction utilize its waste to create more fuel?

    In Britannica's article on nuclear fusion, I came across the following description of the recycle of triton and neutrons: What puzzle me are why the tritons are produced from the D-T fusion reaction, given that the products are alpha particle, neutron, and energy; and how the neutrons can be...
  32. A

    Engineering Problem with the reaction forces in the gearbox

    Greetings, I have tried to find the reactions of the bearings on the Y direction in the intermediate shaft. but I couldn´t find the numerical results of the solutions here is my attempt: in order to find the forces I did the moment equilibruim around the point A and B With FT1 FT2 and...
  33. samy4408

    Question about the rules of thermodynamics

    Hello , we learned in thermodynamics that to calculate ΔHr °(of the reaction ) using ΔHf °(standard heat of formation ), we have to respect that ΔHf °=ΔHr ° of a reaction forming 1 mol of compound from pure elements in their most stable form at standard state . the problem is when we want to...
  34. G

    B General Relativity: Action & Reaction in Gravitation

    Hi, In general relativity, gravitation is not anymore a Force but a deformation of space time. I would like to know what's becomes the 3 law of Newton for gravity that action equal reaction ? When a apple fall on the earth, does "the force" is exactly the same as the one applied on Earth ...
  35. barryj

    Chemistry Understanding the heat of reaction

    Since the heat of formtion of H2O is -285.8 and the heat of formation of CO2 is -393.5 I thought that the heat of reaction CH4 + 2O2 should be -393.5 + 2(-285.80 = -965.1 Where am I wrong?
  36. samy4408

    Medical Question about reactions in biochemistry

    we assume that we have an exergonic reaction , a substrate going to a product , is the negative ΔG′° the principal reason that the equilibrium favors the product (there is more product than substrate at equilibrium )?, or it is not and that depends on other factors? , thanks .
  37. G

    To find the reaction in a system at a ring

    Could I ask for a hint as to where to go next with this question please? I've done this first part, to find the reaction on the wall. Here's my diagram: I've labelled the internal forces at B in red. In green I've shown the reaction at the ring. So I need to find sqrt(Rx^2 + Ry^2) = R. So...
  38. hagopbul

    Mysterious Reaction to Small Magnet: Investigating an Unexplained Phenomenon

    Hello All : Good day : i found a small magnet and it reacted strangely with my body , the magnet is 5 mm in diameter , and less than 4 mm thickness , i rob it few times on my left hand vain it stuck , which i do not understand why ! i checked on other people about 3 one of them had the same...
  39. Huzaifa

    Acid-base reaction equilibrium

    $$ \begin{array}{c} \mathrm{HA}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{A}^{-}+\mathrm{H}_{3} \mathrm{O}^{+} \\ \mathrm{K}=\dfrac{\left[\mathrm{A}^{-}\right]\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]}{\left.[\mathrm{HA}] \mathrm{H}_{2} \mathrm{O}\right]} \quad...
  40. 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...
  41. Ineedhelpwithphysics

    Action Reaction Spring Scale Question

    Here is the image the answer is say 100 but why. Why isn't it 0. Is it because of the pulley but even with the pulleys the tensions in both ropes are 100 N.
  42. SpectraPhy09

    Chemistry The reaction of Benzene Diazonium chloride

    I think that since the -Oh group is attached it would be activating the ring so either ortho product will be formed or the para product. So I'm confused between option b & c (Given and in my textbook is C). Plz can someone help me with this
  43. SpectraPhy09

    Chemistry React Aniline w/ Br2: Mechanism & Desired Product

    I was thinking to react Aniline with Br2 in presence of Ch3ch2-Oh But I don't know the mechanism also I'm confuse will this really give the desired product In my textbook, they reacted aniline first with an aldehyde and then with bromine water, and then with H+ to get Desired product .. I want...
  44. H

    Calculating joint reaction forces

    I have this question in my biomechanics class, and the way the teacher has solved it raised some questions with me. This is the snippet of work from the lecture slides: But, if we see the red variables acting as 'placeholders' for the value of respective forces, and the value of the force at...
  45. S

    I Base Motion and Vertical Beam - Basic Reaction Forces?

    So I am trying to understand how to estimate the amount of deflection [D] the vertical beam shown above would experience if the base it is attached to is accelerating at a constant acceleration [a] of 9.81 m/s. I assume the Force [F] would be equal to weight of the vertical beam (mass x...
  46. Guidog77

    B Balloon rocket- What happens inside and why the reaction?

    The law of action and reaction is the explanation that I see everywhere. But I can't find anywhere what exactly pushes the balloon in the opposite direction as the air coming out. Air molecules come out to where pressure is less. What exactly moves the rubber balloon in the opposite direction...
  47. dckemp1999

    Reaction between marquis reagent and ibuprofen?

    How did you find PF?: Social media Hello there good people, I would like to know what is the product of the reaction between marquis reagent and ibuprofen? CH2O is Formaldehyde, SO4 is Sulfuric Acid and C13H1802 is ibuprofen The reaction is CH2O + SO4 + C13H1802 = ?? I was wondering what...
  48. G

    COVID Anyone else having a terrible reaction to the COVID vaccine?

    Man this is killing me (figuratively I hope). I know I’m whinging, but I rarely get sick, and here I am experiencing full on flu symptoms along with a slightly discomfortable chest after the 2nd Pfizer. In addition to the sore arm. Being sick sucks, especially when it’s fake sickness meant to...
  49. D

    Calculating Support Reaction Forces using Method of Joints

    Summary:: The question requires us to determine the member forces using method of joints but I couldn’t figure out how to calculate the support reaction forces I tried to use equilibrium equations to solve the question but the force applied will be canceled out, and eventually the reaction...