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.

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  1. W

    What is the Empirical Formula of a Chemical Compound Given Combustion Data?

    Homework Statement 35.0mg of C-H-N (the unknown is the empirical formula) combusts to produce 33.5mg CO2 + 41.4mg H2O Homework Equations I'm confused by the fact the product does not include N so I'm unsure how to figure for it. The Attempt at a Solution Using all the information...
  2. P

    Phase Transitions and Chemical Potential

    Hello, right now, I am learning thermodynamics with Reichl: "A modern Course in Statistical Physics" In chapter 3.C page 100 "classification of phase transitions", the text says: "As we change the independent intensive variables (p, T, x_1,... ,x_l) of a system, we reach values of the...
  3. N

    Engineering Chemical, Software or Electrical Engineering?

    Hi. This is to all the practicing EEs out there. What are some of the challenges of electrical engineering work? Is it varied? What is your role (esp. wrt to EE technologists/technicians)? Preferably, answers will come from various specialties and roles (please state them). For example...
  4. H

    Engineering Chemical Engineering vs. Electrical Engineering

    Hello, I am very new to the forums, and I ran across another form discussing these two topics; however the previous thread was mainly discussing nanotechnology. I am interested to find out which carrier I should pursue: chemical eng. or Elec. Eng.? I am extremely interested in both...
  5. K

    Request for a book: Chemical Thermodynamic by Peter Rock A.

    Hello! Does anyone have a free ebook of Chemical Thermodynamic by Peter Rock A.?
  6. S

    Balancing Chemical Equations with Linear Algebra

    Homework Statement Balance the following Chemical Equation (x1)KMnO4+(x2)MnSO4+(x3)H2O->(x4)MnO2+(x5)K2SO4+(x6)H2SO4 Homework Equations Here is the matrix I came up with but it seems to be flawed but I am unable to see what i am doing wrong 1 0 0 0 -2 0 (K) 0 1 0 -1 0 0 (Mn) 4 4 1...
  7. L

    Chemical Nomenclature: Learn Names, Formulas & More

    Are there any good websites to learn chemical names? I can only find ones that teach a few things, but not everything. I need to be able to know the chemical name just by looking at the formula and vice versa.
  8. K

    Chemical Equilibrium with individual reactions

    Homework Statement Homework Equations Kc = (Kp)/ (RT)delta n K_c = (K_a)(K_b) (Where a and b are the individual reactions while c is the overall reaction where the coefficients are the same) The Attempt at a Solution The question prior to this one has individual reactions as...
  9. M

    Confused - chemical potential of an ideal classical gas

    Can anyone help me. I am very confused about the chemical potential. In the following equation dU = TdS - pdV + u dN, where u is the chemical potential it seems to me that if you add particles to a system you are increasing the energy of that system, i.e. the chemical potential is...
  10. P

    Chemical Potential Energy and Kinetic Energy

    Homework Statement The chemical potential energy in a certain amount of gasoline is converted to kinetic energy in a car that increased its speed from 0 mph to 32 mph. The car accelerated to 64 mph. Compared to the energy required to go from 0 to 32 mph, the energy required to go from 32 mph...
  11. J

    Engineering Biochemistry vs. Chemical Engineering

    i'm not exactly sure what i want my future career to be (my interests keep changing) but right now I'm set on engineering. i did a little research and I've narrowed it down to either chemical or systems design engineering. if there are any chemical engineers out there, why did u choose this...
  12. H

    Chem Kinetics: Suggestions for Further Reading & Calculus-Based Texts

    I've been independantly studying chemical kinetics from a standard freshman year chemistry textbook, and I enjoy the subject, could anyone suggest any further reading or sources? Specifically I'd like to try and find a calculus based text, as the one I have specifically avoids using any...
  13. Pythagorean

    What are the fundamental forces involved in the chemical reaction?

    I'm assuming the standard reductionist viewpoint: that chemistry is simplified quantum physics. Of the four fundamental forces in modern physics, what forces play a role in chemical reactions? Is it safe to assume it's solely electromagnetics?
  14. C

    How many REU's should I apply to? (Sophomore Chemical Engineering)

    Hey guys, I'm currently a sophomore chemical engineering major and I'm looking to do an REU related to physical or organic chemistry, or chemical engineering applications. I know most people here would be math or physics or other engineering majors, but I'm just wondering if anyone who had a...
  15. C

    Balancing Chemical Equations Using Oxidation Numbers

    Homework Statement http://carlodm.com/pictures/problem.png The Attempt at a Solution I'm stuck. Usually I balance the equation by multiplying the Fe(OH)2 and Fe2O3 by 3. However, I can no longer do this because Fe2O3 has two iron's per one molecule. Do I multiply one by 6 and...
  16. M

    How to Determine Chemical Potential of 44 ^6Li Atoms in a 3D Harmonic Well?

    Homework Statement What is the chemical potential, \mu (in units of \hbar\omega) at T = 0 K of 44 ^{6}Li atoms with spin 1/2 contained in a 3D harmonic potential well (energy levels, \epsilon_{i}=(i+3/2)\hbar\omega with degeneracies g_{i}= 1/2(i+1)(i+2) )? Homework Equations The...
  17. S

    How Do You Solve the Steady-State Heat Equation for High Activation Energy?

    Homework Statement the math in here is a bit over my head. the equation is \frac {d^2 \theta}{d x'^2 } = -y *exp(\theta) eq. 1 first off, this is a steady state model. meaning, we consider the pre-explosion temperature to be small in comparison with the absolute temperature of the walls...
  18. M

    Derivation of Chemical Potential

    Homework Statement Derive the following: \mu_i=T\left( \frac{\partial S}{\partial n_i}\right)_{U,V,n_j\not=i} \mu_i is the chemical potential of the ith component G is the Gibbs free energy Homework Equations dU = TdS - PdV + \sum_i \mu_i dn_i \mu_i =...
  19. S

    Chemical composition of solar system

    If our solar system originated from the same dust / gas cloud, why do we see such differences in abundance of elements from one body to another. I can come up with two possible answers: 1. Rotation of cloud centrifuged heavier elements towards edge (Almost certainly not true, because it would...
  20. X

    How Does Pressure and Temperature Affect the Chemical Potential of CH4?

    Homework Statement Calculate the change of chemical potential of CH4 in a transformation from the initial state using the ideal gas law. σi={pi=1atm, Ti=298.15K} to the final state σf={pf=100atm, Tf=400K}. any ideas?
  21. P

    Is Yellow Southern Pine resin a viable alternative for heating homes?

    Just out of curiosity, has anyone ever heard of using sodium thiosulfate pentahydrate (liquid crystals) as a viable method of heating a house? I'm doing a project on this now and it seems hugely inefficient due to the massive amounts of crystals that would be needed to produce enough energy to...
  22. M

    Balancing chemical equations and calculations using equations

    Hi there, Had a fair bit of hoework my first day back with no answers. Would anyone mind looking over these to see if i did them correctly? Thank you for your time. http://img42.imageshack.us/img42/5117/46730937.jpg http://img35.imageshack.us/img35/4489/56478985.jpg...
  23. E

    Can Silver Be Scientifically Harmful to Werewolves?

    I'm writing a book but my chemical knowledge is near non-existent and I need a TRUE scientific reason as to why warewolves would be 'allergic' to silver. I know I could make something up but I would like to have as much fact as I can when it comes to stuff like this. It'll help me stand out.
  24. H

    Why Does Reactivity Increase Down a Group in the Periodic Table?

    Homework Statement Why does the chemical reactivity increase as we go down in a group? Homework Equations none The Attempt at a Solution I know it has to do with the atomic radius... but I'm not sure :P
  25. C

    Chemical Potential & Fermi Energy

    Hi there, i've already read some topics in this forum about the fermi-energy/chemical potential. I've also read the article "The chemical potential of an ideal intrinsic semiconductor" from Mark R. A. Shegelski which made the whole thing a little bit more clear to me. but there are some...
  26. E

    Material science v.s. chemical engineering?

    what's the difference? it looks like a chemical engineer and material scientist does the same thing
  27. I

    What Are the Products of NaClO and Na₂SO₃ Reaction?

    Homework Statement Do anyone know the product of: NaClO+Na_2SO_3 The thing is, while searching online, I found: Na_2SO_4+NaCl While the instructor had something along the line of (and he himself isn't sure of the answer, since he is not the one who wrote it): Cl_2+Na_2SO_4+H_2O Or...
  28. D

    Verifying Beam Reactions: A Chemical Engineer's Challenge

    Hey. Im currently doing a course in numerical analysis, and while most of the focus is on the mathematics side of things, the assignments are set in an engineering context. One of my assignments describes a beam that is "pin jointed" at both ends, is 1 meter long, and is subject to a 0.5 N/m...
  29. C

    Chemical Amount: Hydrogen & Oxygen Ratio?

    Chemical Amount?? Hey guys, I'm looking for a little help with the whole concept of chemical amount. This question was posed during my intro chem lecture (assume a hydrogen atom's mass is 1 amu, and an oxygen atom's mass is 16 amu): How much oxygen does one need, to have the same number of...
  30. M

    Not a questionCan Someone Verify My Balancing Chemical Equations Homework?

    Homework Statement Could someone verify if these are correct, my text does not provide answers and i have a test tom. Thank you very much. http://img251.imageshack.us/img251/9319/lastscanx.jpg http://img251.imageshack.us/img251/886/lastsc1an.jpg...
  31. I

    Chemical Reactions: Why we Use Symbols with Numbers

    I was wondering how come when ever there's a question like aluminum reacts with bromine it is usually written like Al + Br2? or Potassium reacts with oxygen is K + O2? How do we know when there's 2 of them?? Is there like a special rule? Why isn't there K2 or Al2??
  32. F

    What Chemical is Used to Neutralize Odors from Decomposing Bodies?

    Just a quick question. Whats the name of the chemical that kills odors which come from decomposing bodies? Thanks in advance, fawk3s
  33. I

    Chemical equation for glucose osazone and limiting reactants

    Homework Statement Okay, a while ago, I did a lab that had me get glucose osazone (C18-H22-N4-O4). Now, I am trying to calculate the theoretical mass of the osazone. The chemical equations goes as follows: C6-H5-N2-H3*HCl + Na-C2-H3-O2*H2-O ------> C6-H5-N2-H3 + H-C2-H3-O2 + Na-Cl +...
  34. P

    How can I balance this chemical equation?

    Homework Statement I am to balance the following equation: Al(OH)41-(aq) + H2SO4(aq) ---> Al(OH)3(s) + H2O + SO42- The attempt at a solution Al(OH)41-(aq) + H2SO4(aq) ---> Al(OH)3(s) + 3/2H2O + SO42- The bolded part above is all I could add to the equation, but I now need to balance...
  35. H

    How Do You Balance CaCO3 + Al2SiO5 ---> CaO + CO2 + Al2O3 + CaSiO4?

    [b]1. Ok here it is, this is one monster of an equation that I have tried and TRIED to balance. hopefully somebody can give me a hand with this thing, thanks in advance [b]2. CaCO3 + Al2SiO5 ---> CaO + CO2 + Al2O3 + CaSiO4 [b]3. What can I say, I've tried repeatedly and can't...
  36. E

    What is the Chemical Composition of Thermite?

    I am trying to find the chemical composition for basic, college chemistry lab quality thermite. I saw that it was a white/grey powder substance. Trying to figure out what the exact chemical composition might be. :)
  37. P

    Doubt in chemical equilibrium question.

    Homework Statement For the chemical equilibrium N_{2(g)} + O_{2(g)} \rightleftharpoons 2NO_{(g)} , the following values were found for the constant Kc (chemical equilibrium constant), at the indicated temperatures: (The table is attached as an image) Table in text format: Temperature (K)...
  38. G

    Chemical equation; reaction; balancing problem.

    Homework Statement All of a sample of Mg(OH)2 was converted to Mg3N2 by: Mg3N2 -> Mg(OH)2 Give the mole ration of Mg(OH)2 to Mg3N2 in that reaction. The Attempt at a Solution Well I'm having trouble just making heads or tails of the equation in the first place...
  39. H

    Balancing equation - What is the chemical formula of cement?

    There are 2 parts to this question: 1. If limestone (calcium carbonate) and clay (assume aluminum silicate) are mixed together and heated then the result is cement. Cement is a mixture of calcium oxide, carbon dioxide, aluminum oxide, and calcium silicate. These bags can be purchased at any...
  40. C

    Chemical to cut headlight oxidation?

    My friend needs to clean his head light lenses and they are plastic , does anyone know a chemical that will dissolve plastic or clean the lens to cut the oxidation , i could buff the lens but i would rather use a chemical, I was thinking along the lines of lacquer thinner.
  41. T

    What am i doing wrong with this chemical formula?

    I think this chemical balance is correct but I'm not sure if I am writing it right or not. Any help?
  42. Y

    Write the chemical equation for the formation of ozone.

    Homework Statement Ozone can be prepared from molecular oxygen by subjecting oxygen to an electrical discharge. The standard free energy of formation of ozone is +163.4kJ/mol. a) write the chemical equation for the formation of ozone. b) what sign of the entropy change for this...
  43. A

    Thermo: chemical potential as a function of T,V, and N

    Homework Statement Find the three equations of state for a system with the fundamental equation U =(vo\theta/R2)*(S3/NV) For this system, find chemical potential as a function of T,V, and N. Homework Equations \mu= chemical potential \partialU/\partialS = T...
  44. J

    Which chemical makes a basic sol'n? (MC)

    Homework Statement 2. The attempt at a solution The way I understand, they would all dissociate like this: NaCl(s) --> Na(+) + Cl(-) I'm pretty sure the Cl(-) is a Bronsted base, or anything with a -ve charge, but as for the solution as a whole being basic, I'm not sure what they're...
  45. S

    Explanation of a chemical reaction

    Good afternoon, The following experiment+observation is given. I look for the explanation of the observations (means: why 1. a white residuum appears and 2. why a blue fluorescence is detected). Brass consists of zinc, tin and copper, the following reaction shall analyse these...
  46. N

    Why Don't Heavier Elements Sink to the Sun's Core?

    This website gives a break down of the ten most abundant elements from spectrum analysis of the sun http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/961112a.html" Presumably this result is only valid for the surface/near surface of the sun. If there were any heavier elements present...
  47. A

    Smaller Packing Fraction, Higher Nuclear Stability - Chemical Kinetics

    why smaller the packing fraction higher the stability of nucleus ?
  48. R

    Chemical Reactions Homework: Copper & Silver Nitrate Reaction

    Homework Statement When copper metal is placed in a beaker containing a solution of silver nitrate, a reaction occurs which can be represented by the following equation: 2AgNO3(aq) + Cu(s) -----> Cu(NO3)2(aq) + 2Ag(s) a) Give the net ionic equation to represent this reaction occurring...
  49. C

    What is KMnO4 in Acidified Dilute Form?

    is KMnO4 the molecular formula for Acidified dilute potassium permanganate
  50. D

    Help with Chemical Equations - Mn(NO3)2, MnO2, H2O2, O2

    Hey guys, I nd sme help with sme chemical equations that I hve. I've tried different sources but they seem to be contradicting each other. Please help. 1. When Mn(NO3)2 is heated, MnO2 and a brown gas J are formed through decomposition. What is gas J? I tried to cancel out the similar...
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