What is Chemical reaction: Definition and 131 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. D

    Engineering Tubular Reactor with catalytic walls

    My attempt: Species fluid and solid phase balances for a tubular reactor in which there is a homogeneous first order reaction and a heterogeneous reaction on the external surface of non-porous catalyst coated along the reactor wall. Mole balance equation for the fluid phase The heterogeneous...
  2. Adrian Tudini

    Energy level diagram of a chemical reaction

    Hi For a personal project, has the energy level diagram of the below reaction been derived? Voltage Applied4B+2LiNO3+C ------------->B4C+2LiNO2+O2 Thanks,
  3. Kiah Palmer

    Chemistry Mass of an element required for a chemical reaction equation

    Conversion: 9.65 kg = 9650 g Mass Al = 26.98 g/mol Molar Mass Al2O3 = (2 x 26.98) + ( 3 x 16.00) = 101.96 g/mol Mol Al2O3 = 9650 g / 101.96 g/mol = 94.65 mol Mol Al Required = 94.65 mol x 2 = 189.3 mol Mass 100% Al required = 189.3 mol x 26.98 g/mol = 5.107x103 g Mass 80% Al required =...
  4. Kiah Palmer

    Chemistry Homework Help: Calculating Mass from Chemical Reaction Equations

    1a) Step 1: Balance the equation - S8 + O2 -> SO2 = S8 + 8O2 -> 8SO2 Conversion (t to g) 6.00 t = 6x10^6 g Molar mass SO2 = 23 + (2 x 16) = 64 g/mol 6x10^6 g / 64 g/mol = 9.375x10^4 mol SO2 reqired amount Sulphur = 9.375x10^4 mol / 8 mol = 1.172x10^4 mol S8 Molar mass S8 = (8 x 32)...
  5. StanG_80

    Dangerous chemical reaction?

    Hello, I mixed these today: H3PO4 NaOH Tetrahydrofuran CH₂)₄O Cyklohexanon C6H10O 2-Butanon C4H8O It started to generate smoke. Just wondering if this gas might have been dangerous to breath in? theories? experiences? Thanks Stan
  6. Adrian Tudini

    Setting up an experiment for a chemical reaction

    Hi I am trying to safely setup an experiment to measure a chemical reaction with a spectral detector. I was wondering how to setup the experiment safely in front of the spectral detector? Do I have to perform some calculations based on the chemical reaction beforehand? Or what? This is an...
  7. somasimple

    Energy of a chemical reaction

    Hi all, Is this energy equation of any meaning if there is no chemical reaction $$\triangle G= RT ln \frac{C_1}{C_2}$$ in compartments with concentrations $$C_1 \ and \ C_2$$ Thanks.
  8. Adrian Tudini

    Actual yield of a chemical reaction

    As in the summary, my question is : has the actual yield of the above reaction being determined experimentally?Thanks.Adrian Tudini
  9. Adrian Tudini

    Computer models that predict the maximum power of a chemical reaction

    Given a balanced chemical equation, can we predict using computer models the maximum power of the chemical reaction? Thanks.
  10. Rahulx084

    What is the Validity of the Rate Equation in Different Reactor Types?

    What is the definition of rate ##(-r_a)=-\frac{dCa}{dt}## or ##(-r_a)=-1/V\frac{dNa}{dt}## ? I think the general one is the second one and first one is for constant volume reaction system. Is the above written rate equation only valid to batch reactor? If not can we use this in a PFR or MFR? In...
  11. D

    Help with balance of matter with chemical reaction

    The question arises in which procedure to follow, a balance by element or by compound? The excersise is this: A mineral of a process contains contains 90% FeS2 and 10% inerts by weight. This materialit is calcined with 25% excess air, according to the reaction: FeS2 + 02 ► Fe203 + S02 The...
  12. Adesh

    How can I understand a chemical reaction?

    I’m a high school student, I generally get problem in chemical reactions. I understand all physical and chemical properties of a compound, for example carboxylic acid have all the acidic property and aldehydes are highly polar. But the problem comes in chemical reactions like shift of positive...
  13. A

    1st law of thermodynamics with chemical reaction?

    ##dU = dw + dq ## vs ##dU = dw + dq + µdN## Which equation do we apply to a closed system involving chemical reaction? According to textbooks, the first equation holds for any closed system in the absence of fields and kinetic energy. However, later chapters use the second equation for...
  14. maistral

    Chemical reaction that can be used for baby gender reveal

    Hi. Basically, the title. I've been thinking about combining phenolphthalein and bromothymol for this purpose. Will this work? Thoughts?
  15. J

    Water sometimes drips from the exhaust of a running car....

    Homework Statement You may have noticed that water sometimes drips from the exhaust of a car as it is running. Is this evidence that there is at least a small amount of water originally present in the gasoline? Homework Equations not sure if there is one. The Attempt at a Solution I'm not...
  16. Rahulx084

    Chemical Reaction Engineering

    I'm confused in the balancing of a reactor , let's say the inlet volumetric flow rate is ##v_○## and outlet volumetric flow rate is ##v_1## Doubts: 1) How is the volumetric flow rate and volume of the reactor ##V## are related to each other ? 2) If the volumetric flow rate is constant (...
  17. dRic2

    Change of P and T after a chemical reaction

    If I have a chemical reaction in closed system, how can I evaluate the change in T and P? I have: - one equation for the chemical equilibrium - one equation for the energy balance but I need an other one! entropy balance, maybe? Thanks Ric
  18. H

    How to write balanced chemical reaction?

    Hi! I've got this problem: 1,20 g of NaHSO4 is dissolved in water to 1,0 liters and pH=2,194. What is the acid dissociation constant for HSO-4? I assume I have to start with writing the balanced reaction, but I don't get how I do that. I know that I'm supposted to start with NaHSO4 + H2O , but...
  19. I

    Chemical reaction vs chemical process

    Hi, I'm hoping to get clear on some chemical nomenclature. A "chemical reaction" is a process that involves some sort of chemical change. But a conformational change doesn't involve a chemical change, just a shape change, thus from what I understand, it cannot be termed a "chemical reaction"...
  20. E

    A very strange chemical reaction

    This is probably the weirdest chemical reaction you'll ever see.
  21. C

    Find the relation of chemical potentials in chemical reaction In hydrogen atom ionization

    Homework Statement In hydrogen atom ionization H→p+e show that ##μ_H=μ_p+μ_r## Homework Equations G=μN (N is the number of particles) The Attempt at a Solution (1) I think the question should say "Find chemical potential relation AT EQUILIBRIUM", don't you think? (2) My professor said that...
  22. B

    Physics of a chemical reaction: looking for textbook recs

    I'm currently doing a literature review on ultracold chemistry with an emphasis on collisional theory and quantum phenomena. I'm an undergraduate physics major, and I'd start my discussion of this topic by moving from basic Newtonian conservation laws and concepts like Coulomb repulsion to the...
  23. C

    I am writing a story involving a hypothetical chemical reaction

    Hello, this is my first posting on this forum. I enjoyed Chemistry in high school, though the arts were where my abilities drew me. I've learned that a ratio of 2 hydrogen to 1 oxygen, when ignited by a certain amount of heat, will create a small amount of water. I will give a brief outline on...
  24. B

    Combustion of Toluene with 30% excess air (Himmelblau)

    Homework Statement Toluene, C7H8, is burned with 30% excess air. A bad burner cause 15% of the carbon to form soot (pure C) deposited on the walls of the furnace, what is the Orsat analysis of the gases leaving the furnace?Homework Equations C7H8 + 9 O2 => 7 CO2 + 4 H2O 30% excess of air What...
  25. herbertpbarreto

    Chemical Reaction Engineering homework

    Homework Statement The decomposition of phosphine 4PH3(g) + P4(g) + 6H2(g) is first-order with respect to phosphine with a rate constant k = 0.0155 s-l at 953 K. If the decomposition occurs in a constant-volume batch reactor at 953 K, calculate, for 40% conversion of PH3, (a) the time...
  26. T

    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...
  27. I

    Do exactly the same chemicals react with each other

    Not sure if this is well know but for some reason, I don't know if exactly same chemicals make chemical reactions with one another and if yes, how common that is?
  28. A

    Calculate ΔHo for the chemical reaction:

    Homework Statement Homework Equations The Attempt at a Solution 2(255) - [(1)(159) + (1)(243)] = +108KJ The answer key says its b) -108KJ. Am i doing something wrong or is the book wrong?
  29. S

    Question about the viability of a chemical reaction

    For organic chemistry we typically look at the stability of the end product to determine if the reaction will proceed. For instance for an Sn2 reaction we would check if the product anion is more stable or less stable than the nucleophile attacking - if the product anion is more stable than the...
  30. F

    Heat slowing down chemical reaction?

    I was doing a science experiment involving enzymes and hydrogen peroxide, and by adding heat to the catalase, it should have sped up the reaction, but instead it slowed it down. Is there a reason why this happened?? Isn't heat supposed to speed up the reaction, instead of slowing it?
  31. Icy98

    Activation energy for chemical reaction

    Only particles that possesses enough energy to overcome the activation energy and orientated correctly will collide and form products. How about those particles which do not possesses enough kinetic energy to overcome the activation barrier? Does it mean that for a particular chemical reaction...
  32. Dr. Who

    I Mass to Energy Transformation for ordinary Chemical reaction

    Hi, My Modern Physics lecturer is of the opinion that the energy dissipated during exothermic reactions is due to infinitesimally small change in mass of the reactants. Similarly, he said that an infinitesimally small part of the food we eat gets converted into the energy using which we perform...
  33. E

    Entropy of a chemical reaction

    Homework Statement The entropy change of surrounding is greater than that of the system in a/an (A) exothermic process (B) endothermic process (C) both (A) and (B) are correct (D) none of these are correct Homework EquationsThe Attempt at a Solution ΔStot = ΔSsys + ΔSsurr For a spontaneous...
  34. Comeback City

    How do I safely react NaOH with HF to yield H20 and NaF?

    I have been reading about how NaOH (Sodium Hydroxide) reacting with HF (Hydrofluoric Acid) yields the products H20 (Water) and NaF (Sodium Fluoride). If I were to do this, would I need the EXACT same quantity of NaOH as HF to get H20 and NaF?
  35. Lee power

    Chemical reaction metal underwater

    Hi guys I was wondering of someone on here could briefly enlighten me on the chemical reactions that would occur with a Teflon Coated high carbon steel hook and a lead sinker while underwater? I am looking into the signals that may or may not be given off by these items both separately and with...
  36. Stephanus

    Wolfram Alpha for Chemistry

    Dear PF Forum, Do anybody know the 'Wolfram Alpha' for chemistry? For example. If I enter: HCl + NaOH The website will produce something like HCl + NaOH -> NaCl + H2O (+ or - energy would be preferable) or if I enter: C6H12O6 + O2 The website will produce something like: Do you mean: C6H12O6 +...
  37. R

    Relating excited state molecular emission to chemical reaction

    .. reaction. This may seem a nonsensicle question but I'll go ahead anyway. Say if I have a process that has an emission spectra dominated by excited state molecular emission, can I relate this in any way to the amount / number of chemical reactions occurring? Thanks for any help
  38. T

    Irreversible chemical reaction

    Hello, "Reversible processes are at equilibrium : Driving force is only infinitesimally greater than the opposing force Process occurs in a series of infinitesimal steps, and at each step the system in at equilibrium with the surroundings It would take an infinite amount of time to carry out...
  39. MexChemE

    Diffusion -- Tarnishing of metal surfaces

    Homework Statement Problem 18B.13 from Transport Phenomena, BSL. Tarnishing of metal surfaces. In the oxidation of most metals the volume of oxide produced is greater than that of the metal consumed. This oxide thus tends to form a compact film, effectively insulating the oxygen and metal from...
  40. Y

    Calculate the force of an explosion from chemical reaction?

    Example, I have a mixture of 5 grams of oxygen and 10 grams of hydrogen. I ignite them. How much force will the explosion do? Yes, I did think about posting this in the chem category but this is about forces, right?
  41. J

    How to know the products of a chemical reaction?

    Homework Statement I am having trouble on knowing what products are formed in a chemical reaction, such as these : i) aluminium oxide and sodium hydroxide Al2o3 + 2NaOH + 3H2O -> NaAl(OH)4 How do we know that we have to add H2O? And how we know that the product is NaAl(OH)4 ? Why can't it be...
  42. pinochet

    Is fusion a chemical reaction

    im reading a chemistry text and its says in daltons law chemicals can not change into atoms during a chemical reaction.but if fusion is a chemical reaction then this is wrong beacuse in stars for example hydrogen combine with hydrogen to form helium .i guest i need a little clarification of...
  43. Y

    Produced bubble in a chemical reaction

    Hi, I have a very interesting but challenging question. Consider any chemical reaction that involves gas production (e.g. H2 gas is produced in KOH etching silicon). As we know, the produced gas will detach from the surface and reaction can continue. What if the gas doesn't detach from the...
  44. A

    State of matter in chemical reaction

    Does anybody know where I could find worksheet to practice naming the state of matter in chemical reactions (with answers in the worksheet to check) as I have problems with that. Especially deciding when it is aqueous. I know (well at least i am right) that when you have acid as reactants it has...
  45. MexChemE

    Pyrite roasting -- Mass balance with chemical reaction

    Homework Statement A certain pyrite ore contains 85% of FeS2 and 15% of inerts. This ore is introduced into a roasting furnace with 20% excess air, in order to oxidize the FeS2 in the reaction: \textrm{FeS}_2 + \frac{11}{4}\textrm{O}_2 \rightarrow \frac{1}{2}\textrm{Fe}_2 \textrm{O}_3 +...
  46. T

    Chemical Formulas: Interpreting Single Atom Reactions

    This is a very basic question. When I see a chemical formula, like for example combustion of methane: $CH_4+2O_2->CO_2+2H_20$ and I compute the standard enthalpy of reaction $H_r$, do I have always to think about this value $H$ and about the chemical reaction as describing a "certain amount"...
  47. G

    Prove Conservation Laws Prevent H+H->H2 Reaction

    Homework Statement A simple and very violent chemical reaction is H + H -> H_2 + 5 eV (1eV = 1.6x10^-19 J, a healthy amount of energy on the atomic scale). However, when hydrogen atoms collide in free space they simply bounce apart! The reason is that it is impossible to satisfy the laws of...
  48. S

    Kinetic equilibrium of chemical reaction

    I was thinking about this: Let's consider a dissociation of some chemical that can run in both directions: AB\rightleftharpoons A^{+}+B^{-} Dissociated form is soluble in a solvent and undissociated form is not - it precipitates. Then the reaction proceeds to the left much faster than to the...
  49. MexChemE

    Enthelpy balance equation

    Hello PF! I have a very short question. We're currently doing enthalpy balances for chemical reactions in our Thermo class. We are using the simple enthalpy balance equation: \Delta H_{\textrm{Reaction}}^0 = \sum \Delta H_{\textrm{Products}}^0 - \sum \Delta H_{\textrm{Reactants}}^0 My question...
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