Reaction Definition and 1000 Threads

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. P

    How many grams of Zn reacted in this reaction (very easy chemistry question)

    Homework Statement The reaction between zinc and hydrochloric acid is carried out as a source of hydrogen gas in the laboratory: Zn(s)+2 HCl(aq)\rightarrow ZnCl_2(aq)+H_2(g) If 325 mL of hydrogen gas is collected over water at 25°C at a total pressure of 748 mm Hg, how many grams of Zn...
  2. J

    Electrolytic cell half reaction equations?

    Hi everyone, I was just wondering how I would choose which species in an electrolytic cell to use as the cathode and which to use as the anode. For example, for aqueous aluminum chloride (inert electrodes), H2O (-0.83V) and H2O (+1.23V) will be used as the anode and cathode for the half...
  3. I

    Solving a Dilute Barium Hydroxide-H2SO4 Reaction

    Homework Statement Barium hydroxide is soluble in water. What are the spectator ions in the reaction of a dilute solution of barium hydroxide with hydro-sulfuric acid? Homework Equations The Attempt at a Solution The chemical equation is: Ba(OH)_{2(aq)}+H_{2}SO_{4(aq)}...
  4. M

    Physical Chemistry Problem, Evacuated tube - where does reaction take place?

    Homework Statement Two balls, one soaked in concentrated HCl and the other in NH4OH are placed at the left and right ends of a 1m long evacuated glass tube, respectively. HCl and ammonia vaporize and travel down the tube, reacting to form a white ring where they meet. Where does the ring form...
  5. K

    Working out support reaction of a frame - Statics

    Homework Statement For the frame shown (see attached picture) , work out the horizontal reaction at B (ie find Bx)Homework Equations EQUILIBRIUM EQUATIONS: sum of moment = 0 (CCW is positive) sum of vertical forces = 0 (up is positive) sum of horizontal forces...
  6. G

    Exploring the Mechanics of Thermite Reactions

    I have three questions about thermite. 1. Is hydrogen released when thermite is placed in water or is it just steam? 2. How can I separate the aluminum oxide from the iron after the reaction? 3. Can the aluminum oxide be split apart into oxygen and aluminum?Any knowledge would be greatly...
  7. J

    Finding the force of reaction as a function of time

    Homework Statement the only part of the question I am unsure about is finding the force of reaction as a function of time Homework Equations F=Ma F=-Kx The Attempt at a Solution F=Ma F=M(Dv/Dt) F Dt= M Dv i integrate force with respect to time from final time=t and...
  8. N

    What is the pre‐exponential coefficient for this reaction?

    Homework Statement I have two problems with this: 1) I am not sure if I am using the right constant. 2) I have no idea if my values are realistic. The actual question: The rate of a reaction is 25.00 units per time at 20.00°C. The activation energy barrier for this reaction is 1.50 eV. a)...
  9. Weissritter

    Graphic representation of xantoprotheic reaction

    Homework Statement O hai, my minions. So...we made the xantoprotheic reaction in the lab, but I have to attach the representation of the reaction. I haven't found it anywhere. So I came to you. Homework Equations Protein + NaNO3→(180s@373K)→(room temp) + NaOH→ Weird yellow precipitate...
  10. M

    Spontaneity of a reaction with ∆G=0

    Homework Statement Note: the following question is from a recent biochemistry exam, for which the grades have been posted and the exam questions and answers have been made available to students. I asked my professor about the answer to this question, and when I explained the issue, we resolved...
  11. J

    Energy required for a chemical reaction

    Hi all, I'm looking for the energy required for a 2-step chemical reaction: CaSO4 + S2 -> CaS + 2SO2 CaS + 3CaSO4 -> 4CaO + 4SO2 This reaction is to happen around 1600 deg. F. I solved for the heat of reaction for these two reactions with the following enthalpy equation: H2=H1+∫CpdT I...
  12. B

    How Do you Calculate how many x rays are coming off a fusion reaction?

    Hello, I'm trying to figure out how to calculate how much energy is being released in a nuclear fusion reaction from x rays. I think it will have to do with how much deuterium is in the vacuum chamber, how many volts I am using and the amount of resistance of the mesh the electricity is...
  13. O

    Find Products of Reaction A-L | Choose from List

    I need to find the product/s of a reaction, which has to be chosen from the list of compounds A - L. I thought the answer was only K but it seems to be wrong or that there is another product to add. (See the attachment). Thanks!
  14. E

    Show the following reaction cannot occur (from introductory high energy course)

    Homework Statement This is from Introduction to High Energy Physics by Perkins, question 3.1 Show that the reaction π- + d → n + n + π0 cannot occur for pions at rest. the π's are pions, the d is a deuterium, and the n's are obviously neutrons. Homework Equations Conservation laws I started...
  15. S

    Reaction between propanone and iodine

    Homework Statement Does iodine take part in the rate determining step of reaction between propanone and iodine in acidic medium? Homework Equations The Attempt at a Solution For positive catalyst the rate determining step is the 1st step of the at least 2 steps of reactions after being...
  16. T

    Simple inclined plane reaction question, I need a debate solved

    Homework Statement Two bodies are acting on one another on an inclined surface. Assuming a constant vertical input force and the lower body being vertically fixed in place on the right hand side, what will the angle of the inclined surface affect. In essence, will the vertical component of...
  17. J

    Finding reaction forces for a Beam

    How do I find reaction for loading condition shown in image. I have no idea how to tackle this type of problem. Please help. http://img6.imageshack.us/img6/725/partilaudl.jpg Uploaded with ImageShack.us
  18. C

    Heat of Reaction: KOH + HCl --> KCL + H2O, NaOH + H2SO4 --> Na2SO4 + H2O

    Homework Statement Given that for the reaction KOH(aq) + HCL(aq) ----> KCL(aq) + H2O(l) H = - 54kjmol^-1. What is the quantity of heat involved in the reaction? 2NaOH(aq) + H2SO4(aq) ----> Na2SO4(aq) + 2H2O(l)? Homework Equations Heat of reaction Hrn =heat content of product Hp - heat...
  19. G

    Reaction Forces at A, B, & C in Beam ABC

    Homework Statement http://imgur.com/AjUdF Segments AB and BC of the beam ABC are pin connected a small distance to the right of joint B. Axial loads act at A and at the midspan of AB. A concentrated moment is applied at joint B. Find the reaction at A, B, and C. Homework Equations...
  20. T

    AP Chemistry basic reaction problem

    Homework Statement Solutions of cobalt(II) nitrate and sodium hydroxide are mixed. What are the solubility rules for the hydroxides? and it occurs in a aqueous solution Homework Equations I have no idea how to solve these problems from my chem class lasty year and we will be...
  21. A

    Statics - Finding Reaction at Supports

    Hey I'm just going over a past paper and I've lost the section of my notes RE this topic. I understand how to draw the free body diagram when there is a pin involved, but not when it is connected at 4 points, the fact that they're at an angle is not helping. Any help greatly appreciated...
  22. N

    How does non-ionizing substance prevent reaction reversal?

    How does the formation of non-ionizing substance (e.g. water in neutralization) prevents the possibility of reversing the reaction? thanks
  23. N

    Chemical Kinetics QuestionDetermination of order of reaction

    Homework Statement So the question says for the reaction 2N2O5(g) --> 4NO2 (g) + O2(g) provides a linear plot when P(N205) is plotted against t with a negative slope . The decomposition of N2O5 follows ? Homework Equations The Attempt at a Solution I am guessing that P(N205) is...
  24. D

    Temperature range at which a reaction is spontaneous, Where is the mistake?

    For a chemical reaction we have, ΔH=-114.1kJ and ΔS=-146.4J/K ---> ΔS=-146.4·10^{-3}kJ/K. Question: Determine the temperature range at which the reaction is spontaneous. A reaction is spontaneous when ΔG is negative in the equation ΔG=ΔH-TΔS, so I do: ΔG=ΔH-TΔS 0>ΔH-TΔS -ΔH>-TΔS...
  25. AGNuke

    Allyl Bromide + HBr - Compounds formed during reaction.

    Allyl Bromide, during the addition of HBr gives CH_3-CHBr-CH_2Br CH_2Br-CH_2-CH_2Br CH_3-CH_2-CHBr_2 CH_3-CBr_2-CH_3 My take During the addition of HBr, electrophile will attack first, considering the shift of pi bond in allyl bromide as follows: BrCH_2-CH=CH_2 \longrightarrow...
  26. HelloCthulhu

    Hydronium + Sodium Chloride Reaction

    Hello again forum! I'm doing a few experiments at home with a protonated saline solution and need some assistance. What is the reaction between the hydronium ion and sodium chloride. I think it's: H30(+) + NaCl => H2 + H(+) + NaOH but I'm not sure. :confused: Any advice would be great...
  27. A

    Motor drives for a satellite reaction wheel

    Hi I am working on my M.Tech project. Now i need to identify whether other than brushless dc motor and permanent magent synchronous motor , is there any other possible motor which can drive a reaction wheel in a satellite. please give suggestions
  28. R

    Reaction force of freely rotating rod

    Hi guys! I'm working some problems for our exam in a few weeks and there are a few problems we are unable to solve. One of them is: "A homogenous rod is free to rotate without friction around one of it's ends. Find the reaction force in function of the position of the rod." As you can see the...
  29. A

    Energy of products in endothermic reaction

    How is the energy of products in endothermic reaction more than the energy of reactants When we see the following equation of an endothermic reaction below 2H2O2--> 2H2O + O2 The 2H2O2 has an enthalpy of 2144 whereas the products have and enthalpy of 1424 Kj/mol SO the reactants have more...
  30. J

    Organic chemistry:substitution reaction

    In substitution reaction between bromine and hexane, why the bromine should be in organic solvent? Bromine is already a liquid!
  31. I

    Reaction at roller connecting two cantilever beams

    Homework Statement The problem statement is as stated in the attached image, For a given E and cross section of both beams, I am to find the reaction at roller E that attaches beam AB and DC Homework Equations There should be stress relation equations and reaction equations. First is...
  32. F

    Producing fusion reaction with x rays?

    Would it be possible to produce a fusion reaction(fusing deterium atoms) using x rays instead of high voltages? Scientist are trying to create fusion using laser, which is just focused photons, but if you have energetic photons such as x rays, which would knock the electron of the deterium atom...
  33. K

    Find tension force of a cable and components of reaction force of pivot

    Homework Statement Please see attached photos. I've been drawing and re-drawing diagrams but I'm at a loss. For part a, I've tried a right triangle using the top cable as the hypotenuse. I've tried the force equation (ƩF=ma) but I don't think that's right. I just can't get a start...
  34. L

    The Reaction Between NO2 And H2

    I have heard different things about this reaction and its products. For practicality, I would appreciate a comprehensive formula, including heat/energy on both sides if you wouldn't mind. And for future purposes, it would be great if you could explain why to me. Just a good, wide explanation of...
  35. S

    Rod on a pivot: Linear acceleration and reaction forces

    Homework Statement Homework Equations r * \alpha = atan r * \omega^2 = arad The Attempt at a Solution arad = (L/2)(3g/L) = 3g/2 atan = (L/2)(3g/2L) = 3g/4
  36. M

    Order of reaction with respect to I^- and S2O8^2-?

    What is the reaction order supposed to be for this reaction of each one? I got 1 for I- and 2 for S2O8, but I think it should be 1 for both of them. Can anyone confirm?? These were the numbers I found experimentally The reason for concern here is that I did a ratio because I used twice as much...
  37. K

    Normal reaction, is this a concept we really understand?

    Hi guys ^^ I am still at A level physics, so don't flame me for my lack of knowledge Now i have been taught that for ex: We have a block of wood named A at rest on a perfectly smooth surface. If we analyse a free body diagram, we have a weight mg downwards acting on the block and a normal...
  38. L

    How did they come up with this completed reaction

    This is what the completed reaction looks like Na2CO3 + 2HCl ⇔ 2NaCl + H2O + CO2 My question is how did they get the products in the above reaction. Here is my attempt, but I don't see how to get it like in the above reaction Na2CO3 + HCl ⇔ NaCl + HCO3 The HCO3 breaks down as follows...
  39. G

    Safety of Reacting: What's the Best Way?

    Hi! I write this letter to confirm the safety of a reation. I've heard that one of my friends made his hands injured because he touched it without knowing that it is the sulfuric acid. And, he told me that he washed his hands with the vinegar. Do you think it is right to use vinegar to...
  40. A

    Action reaction force quick question

    Homework Statement A firewoman opens the fire hose, and water sprays forward. What is the action force and reaction force? Homework Equationsnone The Attempt at a Solution I was thinking that the action force would be water pushing on air and reaction air pushing on water? But how...
  41. H

    Chemistry: How do I write an ionic equation for this reaction?

    Homework Statement I was doing this problem for HW online, that asks to write the ionic equation for a reaction, but I'm completely stuck. After using all my attempts (i.e., I can no longer submit the answer even if it is right, :frown: ) I still couldn't get the right answer. We've only...
  42. Z

    How do you get the energy of products in nuclear reaction?

    The radionuclide X has a half life of 2.58hours and is produced in a cyclotron at a constant rate by bombarding a Y target with 2.10 MeV deuterons. The target contains only the stable isoptope Y and the reaction that produces X is Y + deuteron -> X + proton show that energy is released in...
  43. B

    How to tell whether a reaction is an elementary reaction

    How can you tell whether a reaction is an elementary reaction without knowing the reaction mechanism? I had this question on a recent midterm and got it wrong: A -> Product Is this an elementary reaction? I said yes because it has no intermediates. In retrospect there's no way I could...
  44. B

    Action-Reaction Forces: Understanding the Basics

    This is not a question from a textbook, I am just supposing a situation. A book is lying on a table with some friction. If I push on the book, the book will push on me with an equal and opposite force; the book will then push on the table with friction, and, in return it, the table will push...
  45. C

    Magnetic anti torque reaction device

    Hi Have got a device that is puzzling to say the least. The device is suspended by a thread i.e. no interaction with the ground. I am rotating four tubes each containing magnets which are being rotated into the repelling magnetic field of a magnet that is fixed to the body The following...
  46. L

    Redox reaction; standard cell potential

    Homework Statement Find the cell potential of the equations Mg^+2 + 2e- --------> mg E=-2.36v Cl2 + e- ---------> 2cl- E=+1.36v Ans: -1.00v The Attempt at a Solution The answer says that it cl2 should be flipped. And cl2 is the anode But I don't understand why. I...
  47. W

    How the rate of heterogeneous reaction changes with the surface area of catalyst

    how the rate of heterogeneous reaction changes with the surface area of catalyst. can anyone tell me about the equation relating both quantities?
  48. F

    Action reaction forces: what is the reaction to tension?

    hello forum, consider an object attached to a rope and rotating in a horizontal loop. The tension T in the rope provides the centripetal force points toward the center of the loop. But forces always exist in pair (action-reaction). what is the other force in the pair where one of the...
  49. O

    Medical Any reaction between metal and sensitivity skin?

    Three substances of nickel, chromium and cobalt, lead to dermatitis ratio accounted for 25 substances, the first, third and fourth place. Does anyone have any suggestions on what kind of reactions between metal and sensitivity skin? Thanks in advance for any suggestions
  50. agnibho

    Oxidation Number to balance a redox reaction

    Homework Statement Balance Cl2+NaOH -> NaCl + NaClO3 + H2O
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