# Reaction Definition and 54 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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21. ### Light energy and reactions

AgBr →Ag + Br2 This reaction takes place in presence of light energy, but why only light ?? Why not electricity, heat or any other forms of energy?
22. ### Effect of Temperature on Chemical Reaction Equilibrium

here is the question (part I): For part I, I need some assistance, I cannot figure out how to do the question. I know eventually what to do, it's just working out the equilibrium constants I'm having trouble with. So to start, I want to work out the K values at 600K and 800K, I do this by...
23. ### Enthelpy change of a neutralisation reaction

Homework Statement Given the reaction K2CO3(s) + 2HCl(aq) → 2KCl(aq) + CO2(g) + H2O(l), I need to find the enthalpy change in J, given that: The specific heat capacity of water is 4.2J g-1 °C-1, and The mass change of potassium carbonate is 2.98g, and the temperature change was °6C, and the...
24. ### Splitting reaction into horizontal and vertical components

Homework Statement In each of the diagrams (please see attached file (I am sorry for the rotated, the original was in normal form but when uploading it, it was somehow rotated)) and the description of each case below, a particle is moving on a smooth surface, so that the reaction force R acting...
25. ### How to write equations for salt dissolving in water/ionizing

Homework Statement Write separate equations for each potassium salt (KH2PO4) dissolving in water and for the ionization reaction of the weak acid anion that each of these salts contains. Homework Equations None The Attempt at a Solution I just needed to clarify when it dissolves in water do...
26. ### Reaction force in ANSYS

Hey, I have a simple ANSYS model shown in link: https://dl.dropboxusercontent.com/u/104865119/hand_calc.PNG [Broken]. Ansys reaction force in z axis is +121 N and -121 N. Can someone clarify how do you get to this result using hand calculations?
27. ### Reaction force to resist rotation

Homework Statement There is a object traveling at 0,2m/s with a mass of 75,000kg. The object impacts a fixed point at a distance of 3.5m from its center of gravity (COG) and rotates around this point. What is the reaction force at the point of rotation? Homework Equations I think it is...
28. ### Material balance with a reaction (chemical engineering)

Homework Statement Felder & Rousseau 4.73 (p. 184) A mixture of propane and butane is burned with pure oxygen. The combustion products contain 47.4 mole % H2O. After all of the water is removed from the products, the residual gas contains 69.4 mole% CO2 and the balance is O2. What is the mole...
29. ### A2 chemistry - how do i know there's an OH in the products?

This is the question and the answer, the problem is i don't know how to get to the answer top is question and bottom is answer I attempted to divide the gas concentration by 24 to get molar mass, but that didn't work and how am i suppose to know that OH- is one of the products? i guessed...
30. ### B Pushing wall

Dear PF Forum, I have a problem with calculating energy which I should have learned long ago in my high school time. If I push (accelerate) a 1 kg object 1 meter/sec2 for 10 seconds, I spend energy like this. Distance = 1/2 at2. So I would have pushed this object for 50 metres. So I'm using...
31. ### I Method to know if a reaction is allowed

Hi guys. This is my first post here. Here it goes. I'm attending an introductory course on particle physics. By now, I'm supposed to know how to find out if a given reaction, say νμ+p→μ++n (for example) is possible or not. Unfortunately, the rules by which a reaction must abide are still foggy...
32. ### A Formula for calculating neutron flux?

I have a liquid scintillator, the electronics system, and a beam of neutrons from a reactor. How do I calculate the neutron flux? Cold anybody give me a formula or equation? Not this equation: phi = n X v, where phi - flux, n = number of neutrons per cm3, v = velocity of the neutrons, because I...
33. ### B All actions are reactions

My grandson asked me this question: If in fact,as Newton said,all actions are accompanied by an equal and opposite reaction, then there can be no single actions in the universe;all actions must therefor be part of a reaction between two opposite and equal actions,which are in fact also...
34. ### I Simple Fulcrum Force Calculation Question

Hello all, I have a (at what first seemed) fairly simple question about calculating the forces on this fulcrum design I have. Here is an image of the sketch and free body diagram that I drew: Basically, the pivot point in my real life application is actually a cam, but for the sake of this...
35. ### 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...
36. ### Nuclear physics

Homework Statement In a particular nuclear reaction, a neutron moving at 3.6×105ms−1 has a 70% chance of initiating a nuclear fusion reaction. Which of the following options is a possible probability of a neutron moving at 2.2×105ms−1 initiating the same nuclear reaction? I wouldn't be asking...
37. ### Acid/Base Question on acidity of salts

Hi everyone! So I have ZnBr2 and CdCl2, and I am asked to choose the most acidic one. Firstly, I do not understand why both salts are acidic... If my ZnBr2 undergoes hydrolisis, the reaction is ZnBr2 + 2H2O <------> Zn(OH)2 + 2HBr. This would mean that this is acidic as the HBr dissociates...
38. ### Heat - microscope

Hi! is there any microscope or images in which we can see how a matter reacts as it is heated? And how was it proved that when matter is heated their particules vibrate faster?. Tahnk you!
39. ### How could this,Sigma0 decay into Lambda and gamma, happens?

I found an article, titled Electromagnetic Decay of the Σ0(1385) to Λγ , in the arXiv telling that the reaction Σ0→Λ+γ can happen through electromagnetic interaction. However, if I examine the conservation of parity. Parity on the left side is even(P(Σ0)=+), but that on the right side is...
40. ### Calculating reaction forces on 3d object

Hello all, I am in the process of calculating reaction forces on an object, and need some help. Attached is a free body diagram of an object in two different views- one looking from the sides (z-x plane) and one looking it in birds eye view. (xy plane) 7 variables I am looking to solve are...
41. ### 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...
42. ### Activation energy of parallel reaction

Well,I know that the activation energy of a parallel reaction can be determined by the arrhenius equation as (e1k1+e2k2)/(k1+k2) where e1,k1 and e2,k2 are the activation energies and rate constants for the two reacations.now consider the reaction A》B,and A》C since at every instant the reacted...
43. ### Reaction of thiols with vinyl ethers

Homework Statement Find the product: 2. Relevant concepts Thiols react with vinyl ethers according to anti-markovnikov's rule The Attempt at a Solution After reading Jerry March's book, i came to know that it follows free radical mechanism and that is why it gives anti markovnikov's...
44. ### Alkylation of Imines: achiral to chiral compounds

I found this in "March's Advanced organic chemistry" After that step, on using HCl in pentane, you will get 4-methyl-3-Heptanone. So this method was used to convert achiral 2-pentanone to a chiral compound, by first converting it to the compound on left by addition reaction and then using a 2...

We got a light source and the light comes through a slit in a plate. A photon passes through the slit and ends up somewhere on a screen not in the straight direction due to diffraction. The question is, in quantum physics, does the plate feel the reaction of the photon deflection (1) at the time...
46. ### Energy balance -- Physical interpretation of Q

Hello PF! I have a simple question on energy balances. Suppose you have an isothermal reactor where you want to have an exothermic reaction happening at 450 °C. The simplified energy balance for the reactor is Q = ΔH. Supposing ΔH = -150 kcal, then Q = -150 kcal. Does this mean that, a) in order...
47. ### Will Ca(HCO3)2(aq) + 2NH3(aq) react?

Hi, I'm wondering if an aqueous solution of Calcium Bicarbonate and Ammonia would react to form Ammonium Bicarbonate and Calcium Hydroxide. Additionally, would Calcium Carbonate react with Ammonia in solution to form Ammonium Carbonate? Best, EJ
48. ### 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...
49. ### Mechanism of saponification

Homework Statement Problem: I am told that the first mechanism is operative in saponification. The Attempt at a Solution However, this strikes me as wrong because the first mechanism involves the formation of dianion. Using hydroxide ion to abstract a proton and make that particular...
50. ### Exothermic reaction in adiabatic reactor

Homework Statement One mole of gas A, two moles of gas B, and one mole of inert gas I are fed into an adiabatic reactor of variable volume and constant pressure at 25 °C. At this temperature, the reaction yielding liquid R proceeds normally as: \textrm{A} (g) + \textrm{B} (g) \rightarrow...