What is Chemical: Definition and 1000 Discussions

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.

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  1. 7

    Chemical reaction equation, historical question

    I am reading a chemistry book printed in 1805. The chemical reaction equations are written using the equality symbol = instead of the arrow →, which is used in modern times. Anyway sometimes it is still possible to see the "old fashioned" way...
  2. G

    Closest Matching Chemical Fingerprint -what analysis?

    Correlation of data sets, chemical composition I have roughly 80 test results from different samples, each result set is a list of concentrations of various chemical compounds and proteins obtained through gcms (gas chromatography mass spec) There are over 50 of these compound concentrations...
  3. B

    Why does a chemical compound precipitate metals differently than metal

    In a solution of aqua regia (or other acids), if there is a precious metal dissolved, along with other metal ( such as other precious metals or base metals), and you add a powdered metal, you precipitate all the metals lower than it on the reactivity list. If however, you use a chemical...
  4. T

    Do Molarities in Chemical Solutions Refer to the Buffer Volume or Total Volume?

    Hello, I quote from a paper: "...a solution of CuSO4 (1 mM) and NaAsc (2 mM) in 10 mM Tris buffer with 20% DMSO". Does the molarities refer to the 80% volume of the Tris buffer or of the total volume (80% v Tris + 20% v DMSO)? For example, if I want to make 100 mL solution, I have to add...
  5. B

    How to deal with charge imbalance in a chemical system?

    I'm using a program for calculating chemical reactions, but I'm not a chemist. I will use the results for a different type of calculation. Sorry, this is probably a silly question. As input for the program, I am using a chemical system that someone published. it contains: SO4(2-), Ca2+...
  6. D

    Chemical potential for van de Waarls gas

    Hello, In my book, we have two equations to find the chemical potential µj=(dF/dNj) T, V and N constants and µj=-kT ln (ζj/Nj) We calculated the potential of a Van der Waals gas using each of these equations, but the result is not the same, i want to understand why ?
  7. H

    How do we know that chemical bonds are made of electrons(sharing)?

    We all have been studying chemical bonds, specifically covalent, told to us that it composes of electron sharing between participating atoms. But do we have a scientific evidence that somehow conforms or substantiates this theory? For example, We have evidence to 'believe' in electrons. The...
  8. V

    Distinguish covalent and partially covalent chemical bonds

    I read some books which mention about covalent and partially covalent chemical bonds. However, I cannot distinguish between them. Who can help me? Thank you very much!
  9. D

    Schools Graduate School in Chemical Physics

    I'm currently a junior at large state school and am a biochemistry major. I started college in a cell biology major, then realized how much I hated cell biology classes (although I remain fascinated by the chemical reactions and complex chemical structure in living things) and how much I loved...
  10. Entanglement

    Equilibrium Constant: H2+O2->H2O

    H2+1/2 O2 ---------> H20 If the equation is multiplied by 2 Will the equilibrium constant change or remain constant ?
  11. D

    Chemical for cleaning printed picture on plastic material?

    Hi all, I'm david from indonesia. Sory for my english. Can you help me to found a chemical that I can use to cleaning printed picture on plastic material? This is for recycling, means in big volume... Thanks before
  12. M

    Chemical kinetics, reaction order, resistance

    X + Y + Z -> A + C+ + B- Initial Concentrations Z= 4.1 X 10^-3M, X=2.3 X 10^-1M, Y= 1.2 X 10^-1 M. http://s121.photobucket.com/user/marykaywest420/media/81386cf6-e132-4578-8fb5-1024a2a3f3d5_zpscc804723.jpg.html?sort=3&o=0 3. So my attempt included graphing -R/(R∞-R) vs. time. which produced...
  13. P

    How does selectivity work in chemical reactions again?

    I got a bit of a question that needs answering. See, I'm still not understanding how basic selectivity in organic chemistry works. I'm not looking to know the mechanism or anything. Just one simple thing. I'll give the description given from some textbook first: Homework Statement The...
  14. gfd43tg

    Chemical Process Flow Diagram Software

    Hello, Does anyone know of any free software that will allow me to easily create chemical process flow diagrams, that have all the symbols for various components (distillation columns, heat exchangers, etc)? Thank you
  15. M

    Chemical Equilibrium of Reaction's constant?

    I'm currently studying for a test and I'm having problem with this concept: If I have 3 different Equilibrium constants for different reactions like Kc=103, Kc=1 and KC=10-4, which one's forward reaction is most favorable, and which one's reverse reaction is most favorable? Maybe it's the...
  16. S

    Studying chemical engineering looking for some book recommendations.

    Hi guys, As the title suggest I am an student chemical engineer and was wondering if anybody could advise on some good books for the following subjects. I have used spoiler tags to hide the specific areas I will be covering so as to make this post a bit neater. Fluid Mechanics. Process...
  17. caters

    Chemical reaction leading to salt water

    Okay let's say we have water, sodium hydroxide and hydrogen chloride. What do you think is going to happen? Do you think the pH will be the same, a little higher, or a little lower? You have this reaction down here: H2O+NaOH+HCl(assuming they are equal)= H2O+OH-+Na+(positive...
  18. E

    Differential Equations Rate At Which Chemical Amount Changes

    Homework Statement Suppose that a large mixing tank initially holds 300 gallons of water in which 50 pounds of salt have been dissolved. Pure water is pumped into the tank at a rate of 3 gal/min, and when the solution is well stirred, it is then pumped out at the same rate. Determine...
  19. Useful nucleus

    Bounds on the chemical potential of electrons

    In a semiconductor, is the chemical potential of electrons limited to take values only between the valence band maximum and conduction band minimum? Are there circumstances where it can cross these bounds?
  20. A

    Entropy, chemical potential, temperature

    For a thermodynamic system there exists a function called entropy S(U,N,V) etc. We then define for instance temperature as: 1/T = ∂S/∂U μ = ∂S/∂N etc. When taking these partial it is understood that we only take the derivative of S wrt the explicit dependece on U,N etc. right? Because...
  21. C

    Chemical transformation (Decomposition)

    Hi, I was wondering when you need to write the decomposition of a substance, how do you know if the number is going to be a coefficient or subscript ? Example: 2H2O ===>2H2 + 02 would be the answer But why not 2H2O ==> 2H2 + 2O Knowing that we have 2 moles of O in the beginning...
  22. B

    Chemical Kinetics: determining order of reaction

    Homework Statement Good day! I have a question from my chem HW that is stumping me. Although the answer may be simple, it has eluded me for quite a bit. It regards rate laws and constants of reactions. Question is as stated: This reaction was monitored as a function of time: AB --> A + B A...
  23. R

    Substance or chemical reaction, that is highest rate in changing mass

    Hello! What would be the substance, chemical reaction and technique, to have the highest rate of immediate mass change, back and forth, from low to high and back to low again, as many times as needed - using only homemade DIY, non dangerous materials and equipment? My intentions are to...
  24. A

    Half-Filled Band: Explaining Zero Chemical Potential

    In an exercise I look at a square lattice and consider a model where the energy band of the electron is half filled and temperature is zero. I am then supposed to explain why a half filled band corresponds to zero chemical potential. For me the most meaningful definition of the chemical...
  25. A

    About chemical engineering and petrochemical

    I am in grade 12 now and I love chemistry and i wanted to be a chemist , but for some reasons i can't go to science school, so instead i decided that to go to engineering school and become a chemical engineer , but then again i had another problem , they only thing available for now is...
  26. Z

    Engineering What can I do with Chemical engineering?

    Hello, I am concerned for my future. I am interested in Chemical engineering as a subject, but the idea of spending my career making chemicals, being in oil/gas, or even in pharmaceuticals depresses me. I would like to get involved with environmental engineering, or work in sanitation or...
  27. A

    Are Temperature and Chemical Potential Independent in Current Flow Models?

    I have seen various treatments of the chemical potential. Basically it all amounted to a definition of it as a quantity maximizing the entropy for systems allowed to exchange particles. Now this quantity has become quite important in some models I am studying for current flow, specifically an...
  28. M

    Engineering Is there any Chemical Engineers Here

    Hi guys, I just wanted to know a bit about chemical engineering from you guys here.
  29. N

    Understanding the Role of Chemical Engineers: Tools, Processes, and Impact

    Are Chemical engineers like applied chemists? Or are they more like mechanical or electrical engineers using their knowledge of chemistry to make things or processes? What tools do chemical engineers use, like tools to measure or tools to build, or both? What kind of things to chemical engineers...
  30. T

    What type of chemical reaction does not have oxdiztion and reduction

    what types of chemical reaction does not have oxdiztion and reduction...
  31. H

    Chemical Kinetics Homework: Ineq., Mass & English

    Homework Statement Homework Equationsln[A]=-kt+ln[A]0 The Attempt at a Solution In this equation,is it necessary to have [A] to be the concentration? If there is the mass provided only,can I just subsitute [A]=mass? Sorry for my poor english
  32. L

    Theory of everything and chemical bond theory

    Hello, Theoretical physicists assert that quantum mechanic and relativistic world use distinct mathematical models that can not united into one so far. The reason of it, which I do not understand, is the gravity. Once we encompass the gravity in the quantum world (or vice versa), we (maybe)...
  33. T

    Chemical Potential and delta G

    Homework Statement Consider a container with two chambers of the same size separated by a fixed membrane in the middle (permeable only to the ideal solute, but not the solvent). One chamber initially contains 1M of solute, and the other contains 0.5M of solute. Write an equation for the...
  34. I

    Chemical Process Calculations, or Material Balances Question

    All of the related work is in the attachment. If you could please help it would be really appreciated. I've asked a bunch of people in my class, and they're confused also. Thanks in advance!
  35. I

    Chemical Potential: Heat Energy Carried by Particles

    in class, we just learned that the chemical potential was μ=∂G/∂N i'm looking in my book and it says that μ=-T(∂S/∂N) this looks a lot like the partial of heat energy with respect to N. is my interpretation correct? (assuming my interpretation was correct): so qualitatively, the...
  36. B

    Chemical energy to electromagnetic energy transer

    Does anyone know of reaction that can generate a a steady source of light? Preferably one easier to activate than burning of magnesium strips(which is too momentary anyway, I'm trying to make a chemical reaction that can eventually power a photoresistor/ light).
  37. U

    Entropy generation in chemical reactions

    So from the first law for a closed system, dU=dQ-dW=dQ-PdV From the second law, dS=dQ/T + Sgenerated (i.e. the entropy generated) Putting expression of dQ from second law into first law, dU=T*dS-T*Sgen-PdV If s and v are constant, dU= -T*Sgen>0 Hence dU<0 This is a...
  38. F

    Novice want to learn about chemical binding.

    Homework Statement Hello again! I've googled about chemical binding but couldn't find anything that teaches me about it so I thought I'd ask you guys. I have several elements like NH3 CaO H2 CH4 BaBr2 and need to figure out their chemical bindings. I know that a chemical...
  39. S

    Writing a chemical equations

    Compose the equation for the reaction of fluoride with potassium nitrate. State the spectator ions. Here is my attempt: K(NO3)2 + F- = N2O6 + KF Or is it K(NO3)2 + NaF = Na(NO3)2 + FK I think the spectator ions are K- and NO3 Any ideas? Thanks
  40. M

    Chemical Reactor Design Optimization

    Homework Statement Homework Equations The Attempt at a Solution For this problem, my group is having difficulty figuring out how much Styrene is reacting, since we don't know the molecular weight of polystyrene, we can't find the moles of polystyrene, which would be used to aid in finding the...
  41. G

    Why particles flow from high chemical potential to low

    Homework Statement Why does the equation (d2G/dNi2)T,P=(dμ/dNi)T,P>0 tells you that particles will flow from high chemical potential to region of low chemical potential at const. temperature and pressure? Thank you all. Homework Equations dG=VdP-SdT+μdNi The Attempt at a Solution...
  42. C

    Difference between electrochemical equilibrium and chemical equilibriu

    1. What is electrochemical equilibrium and what is chemical equilibrium? 2.What are the differences between the two above? 3. The difference between the two i think is electrochemical equilibrium is a state whereby the electrical charge in both compartments are equals. Wherease...
  43. N

    Engineering Do chemical engineers only work with power plants?

    I looked into the field of chemical engineering because of my interests in chemistry and making things, but I saw only things that involved power plant. Do chemical engineers do anything besides building, maintaining and supervising power plants? Thanks.
  44. T

    Chemical physics vs physics for Bio-Physics

    I have become interested in Biophysics and there are not many programs out there with a BS in Biophysics. I know UCLA and UCSD both have programs but the rest of the UC system unfortunately does not. I will be apply for a TAG (I get guaranteed admissions to some of the UC's if I meet certain...
  45. S

    Chemical Engineering Computation - Rectangular Matrix Formulation

    Hello all, I've got a somewhat mixed concept question from a Chemical Engineering computational methods class. I'm completely lost with this question, as I do not fully understand what it entails. The question (and data) is this: Homework Statement Data Set Given X Y 0.00 -2.17...
  46. D

    Chemical Thermodynamics Course Help/Advise?

    Hello all! I am new here, although I have been reading on here for a few years now. I'll get right to the point. I don't have a specific homework question exactly, but rather I need help with a course. I am a senior biochemistry major, and I am taking Chemical Thermodynamics, my school's...
  47. U

    Variation of chemical potential with T and P

    So the expression for Gibb's free energy is: dG = -SdT + VdP + μdN, Here, we see that the Gibb's free energy changes with temperature (dT), change in pressure (dP) and change in chemical potential (as a result of change in particle number). My question is: we know chemical potential...
  48. U

    Chemical potential vs hydro-static pressure during osmosis

    So when osmosis between two solutions (separated by a semipermeable membrane),takes place, the solvent travels from the side where its chemical potential is higher to the side where its chemical potential is lower. However, this results in a difference of levels of fluids across the membrane...
  49. C

    Engineering Material and Chemical Engineering, which to choose?

    Hi everyone, I'm an a-level student (year 13) doing Physics, Chemistry and Maths. I am struggling of what university subject to apply for...I want to do a subject that is a combination of all three subjects I'm now doing. I like topics that I can go very very deep. I think quantum and...
  50. D

    Pursuing a PhD in Chemical Biology?

    When I started college, I was a biotechnology major. I found this major be a dumbed down version of molecular and cellular biology, so I decided I wanted to switch out of it and major in biochemistry and molecular biology focusing in biochemistry, the problem was that I had already taken two...
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