Chemical Definition and 1000 Threads

A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys. Chemical elements may or may not be included in the definition, depending on expert viewpoint.Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride) and refined sugar (sucrose). However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical.
Chemical substances exist as solids, liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure and time. Chemical substances may be combined or converted to others by means of chemical reactions.
Forms of energy, such as light and heat, are not matter, and are thus not "substances" in this regard.

View More On Wikipedia.org
Recent contents Top users
  1. Karan Punjabi

    Effect of Temperature on Chemical Equilibrium

    Guys, I'm studying about Le-chatelier's principle and the topic is effect of temperature. I just went through it and found a difficulty that why K values changes i.e why the equilibrium constant changes as in other effects like changes in concentration, pressure,etc the K values remains constant.
  2. 24forChromium

    Possibility and detection of this chemical equilibrium

    Dissolve a salt containingCr2O72- and an "inert cation" in water, would the following equilibrium occur in appreciable quantity? Cr2O72-+OH-⇔2CrO42-+H+ If it does occur, I suppose the acidity of the water would affect the equilibrium constant (or at least the relative concentration of the...
  3. 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
  4. M

    How much math would be involved in chemical engineering?

    I am looking into different engineering fields I am only 12 but taking all high school classes and I need to know which career I'm interested in which I've been interested in engineering since I was 5. I want something that requires a lot of math but not electrical engineering...
  5. L

    Gaging Time with Chemical Clocks: A Crazy Idea?

    I am really very new to chemistry and physics, although I hope to study in the future. I have a question regarding chemical clocks. Is it possible to gage time using a specific chemical clock or chemical reaction that you may know of? my first,idea was standard chemical clocks like the...
  6. T

    Are All Chemical Reactions Reversible?

    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...
  7. H

    Engineering Field work of chemical engineering environment

    Can anyone list what is the scope for chemical engineering environment?
  8. Mohiuddin Munna

    Proper chemical to dissolve/decompose adhesive scotch tape

    I put few IC die (GaN grown on Si ) in small plastic case on top of scotch tape so that it can't movie . Now I it firmly stuck on it. I try to move it physically by a niddle and twister and already broke one. I need a chemical which will dissolve the tape including adhesive but not the die...
  9. P

    Engineering Engineering Career Survey Questions: Insights from Professionals

    Good evening, forum members... I'm currently enrolled in an Engineering class in my school and I'm considering engineering as one of my career pathways, but I would like to know the good, the bad, and the prospects of an engineering career before making a decision. I'm also interested to know...
  10. 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?
  11. Crush1986

    Chemical Potential Homework: Ideal Monatomic Gas

    Homework Statement I just have a question about chemical potential for ideal monatomic gas. I see that by definition \mu = \frac{\partial U}{\partial N} Homework Equations \mu = \frac{\partial U}{\partial N} The Attempt at a Solution I was wondering why it is wrong to use U=3/2NkT take...
  12. R

    Explain chemical formulas PO43-

    PO43- I Understand the 4 represents how many oxygen atoms are bonded to the Phosphate. What exactly does the 3 and its - sign represent? By the image, I can tell the difference between the 3 oxygen atoms and the single isolated one, with the double || symbol, has a different electronic...
  13. Coffee_

    How is the chemical potential defined when keeping entropy and volume constant?

    The chemical potential is defined as ##µ=\frac{\partial E}{\partial N}## while keeping entropy and volume constant. Well how to keep the volume constant while adding particles is obvious but what about the entropy? Obviously adding a particle at a certain energy ##E_{p}## changes the total...
  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. 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...
  16. Titan97

    Why is k4 Greater than k3 in Cadmium Complex Formation?

    Homework Statement The formation of cadmium complexes with Br- exhibits successive equilibrium constants such that log(k1)=1.56, log(k2)=0.54, log(k3)=0.05, log(k4)=0.37. Explain why k4 is greater than k3 Homework Equations $$K=e^{\frac{-\Delta H}{RT}}\cdot e^{\frac{\Delta S}{R}}$$ The...
  17. pinochet

    Is Fusion Considered a Chemical Reaction in Stars?

    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...
  18. R

    Understanding chemical depictions.

    https://upload.wikimedia.org/wikipedia/commons/7/70/Phosphat-Ion.svg This image is a depiction for the chemical formula of A phosphate PO4^3− I understand the ^3- represents the the Oxygen atoms. I was wondering what exactly does it mean; I would assume it means the atom has a negative...
  19. J

    Engineering How hard to get an entry chemical engineering position?

    I am a nontraditional applicant with a bachelor's degree in neuroscience. I am almost finished a master's degree in chemical engineering, but many jobs that I wish to apply to have a "bachelor's of engineering" as a requirement. And a master's as only a "preference." Would these companies still...
  20. D

    Engineering Why are there few occupations for Chemical Engineering?

    I was thinking about going through chemical engineering major but then I saw these figures and I was shocked ! http://www.bls.gov/ooh/architecture-and-... There are 33.000 occupations for chemical engineers and, There are 300.000 occupations for electrical engineers...
  21. R

    Clarification on Chemical Formulas

    I was wondering what the upper half of the hexagon represents, I assume the Triangles represent O repeating; and how would this formula be written out in text.
  22. K

    Why the chemical elements are found together in nature

    I've often wondered, but have never found a solid explanation for, why the chemical elements are found together in nature? Why aren't atoms all in a somewhat homogenous mix? Why are X atoms found with other X atoms? And why are isotopes found together, such as Uranium 235 and the far more...
  23. B

    Engineering Career advice for a Chemical Engineer graduating in 2016?

    Hi all, my name is Brandon and I'm new to these forums I'm going into my 5th year at university and am majoring in Chemical Engineering. From my understanding, those who choose to go into industry after graduating are usually in process, petroleum, etc. However, I am rather more interested...
  24. P

    FE Chemical Question: Unraveling the Mystery of 3.24

    Hey Guy, Attached find a problem a couple of my friends and I have been working on at work to study for the FE. We have the solution, but we don't understand the logic behind the mysterious 3.24. Any insight would be appreciated. Kind Regards, Paul
  25. S

    Can Lasers Used for Building Molecules Initiate Nuclear Fusion?

    http://www.iflscience.com/space/molecules-have-been-built-using-laser-beam-first-time Is there a way that fusion could be achieved with coherent control like this? If it can build molecules couldn't deuterium-deuterium be achieved?
  26. I

    Chemical Safety - Storing Ammonium Nitrate

    Hello, I'm thinking about creating a temporary refrigeration device for cooling items in a hot enclosure (i.e closed car in the sun), and I was thinking about using on-demand NH3NO4 as the cooling agent. I understand how the reaction works and the implications of using the chemical, but I'm more...
  27. K

    Kinetic equilibrum and chemical equilibrium

    All particle species are in equilibrium at early times of the universe. But I didn't find any book that makes the difference of kinetic and chemical equilibrium clear. I have some of my own opinions and I hope to get your comments: (1) kinetic equilibrium means the distribution function obeys...
  28. O

    Programs Should I switch out of Chemical Engineering to other major?

    I am currently third year student doing Chemistry and Chemical Engineering Dual Degree and I am currently miserable. Like my many friends who became ChemE majors, I didn't know exactly what I was getting into. I imagined it is like chemistry except more complicated and advanced. I am doing quite...
  29. Kior

    What is the difference between carbon sink and reservoir？

    I am trying to figure out the difference between a carbon sink and a carbon reservoir. The definition for a carbon sink from wikipedia is that “carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period. ” And...
  30. Smoothmusicman

    Chemical/Paint What substance cools when electricity is applied?

    What is a liquid, gas, gel, (substance) etc. that cools when it meets electric current? Thank you all for the help.
  31. K

    Why do phase trxns behave differently than chemical rxns?

    If we have solid water (ice) at -5 C and atm P, then according to thermodynamics, the process that takes that ice (at -5 C & atm P) from solid to liquid is non-spontaneous, which means its ΔG > 0. Hence, it is impossible for someone to observe ice melt to liquid at -5 C, and assuming we started...
  32. C

    Chemical potential equilibrium cosmology

    In Dodelson's "Introduction to Modern Cosmology" at p. 61 he introduces a non- equilibrium number density $$n_i = g_i e^{\mu_i/T} \int \frac{d^3p}{(2\pi)^3} e^{-E_i/T}$$ and an equilibrium number density $$n_i^{(0)} = g_i \int \frac{d^3p}{(2\pi)^3} e^{-E_i/T},$$ from which it follows that the...
  33. vead

    How to Analyze Ion Concentrations in a Mixture of Salts?

    Hello I need some ideas . there are about nine or ten compounds that are present in water [((H3BO3),Ca(No3)2),KNO3, KH2PO4), (K2SO4, (ZnSO4)]how to separate the compounds ? how to measure quantity of each ? I did google search , I got the HPLC , GC , spectroscopy , but I don't understand...
  34. It's me

    Chemical potential of water using the Van der Waals model

    Homework Statement Obtain the chemical potential of water as a function of temperature and volume using the Van der Waals model. Homework Equations μ=∂U∂N The Attempt at a Solution I don't really understand how to do this at all. Any help would be greatly appreciated.
  35. 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...
  36. 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...
  37. V

    Engineering Advancement as a Chemical Engineer

    Hey All, I'm a process engineer with a background in chemical engineering, working in the food/beverage/distilled spirits industry. I have a BS, and am considering pursuing both PE certification, and a part-time MS in ChemE while I work to improve my job prospects/salary. Are either of these...
  38. mooncrater

    How Can Stoichiometry Determine the Order of an Elementary Reaction?

    Homework Statement There was a statement in a question which said: "The order of an elementary chemical reaction step can be determined by examining its stoichiometry. " And it was given correct. Homework EquationsThe Attempt at a Solution But shouldn't it be wrong? Order of a reaction is...
  39. gracy

    Water molecule in chemical formulas of inorganic compounds

    In chemical formulas of various inorganic compounds there are molecules of water .I wanted to know is it important to remember the number of moles of water in chemical formulas of inorganic compounds.
  40. M

    Hi Question related to Gears and their chemical composition

    Hi ! This is Mustafa. I recently did my bachelor's and started working with Honda Motors. So my manager asked me to do a little research regarding the Gear type (SCM415H) used. I have to check how varying the chemical composition of each element will result in the properties of the gear...
  41. gracy

    What Is the Chemical Formula of Bornite?

    What's the chemical formula of bornite?According to wikipedia http://en.wikipedia.org/wiki/Bornite it is Cu5FeS4.According to http://www.spiritofisis.org/knowledge/crystal_files/bornite.htm it is Cu2FeS4 and as per my textbook it is Cu3FeS2.Now,What's the actual chemical formula of bornite?I...
  42. I

    What's the chemical formula of cement and resin?

    Hi, i need to know the chemical formula of cement and resin and their densities. can someone help me, please? thank you in advance !
  43. Emmanuel_Euler

    What is the Most Dangerous Chemical?

    what is the Most Dangerous Chemical or poison in the world?
  44. E

    Chemical equilibrium for simultaneous dissociation reactions

    Hello everyone, Sorry I didn't have the time to rewrite the question, Can you help me with this?
  45. P

    How to dope a chemical compound?

    I am interested in creating phosphors for electroluminescent panels and from what I've read, one of the most common compounds is copper-doped zinc sulfide (ZnS:Cu). I've figured out how to create the zinc sulfide through a simple combustion synthesis reaction but it is the doping part that I...
  46. S

    Heat Transfer - Void Space Dynamic Insulation

    Hi, I currently have a project running involving dynamic insulation. I am struggling to develop a 1D transient analytical model to compare to my experimental results. I have used the separation by variables method in the most basic form over 1 solid material but have failed to adapt this to 3...
  47. 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 +...
  48. H

    Why must chemical equations be balanced?

    Homework Statement Why must chemical equations be balanced (check all that apply). (a) In a balanced chemical equation, the coefficients in front of each reactant and product allow us to predict how much reactants are required to form a given amount of products. (b) In a balanced chemical...
  49. A

    Chemical Potential: Pressure, Fugacity, & More

    Chemical potentials can be written with an an ln term which has pressure, fugacity, concentration, activity coeff times concentration, mole fraction, and mole fraction times activity coeff. Is there any source that makes sense of this?
  50. C

    Can a Microbiologist Pursue a Chemical Engineering Masters Degree?

    How possible is it for a microbiologist ( first degree) to run a masters in Chemical Engineering? Is it a better idea? please advice
Back
Top