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. 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...
  2. D

    Engineering Chemical vs Mechanical Engineering

    I am a high school senior caught between these two fields. they both seem very exciting and I am not sure which would be better suited for my interests. In high school, my favorite subjects have been Physics, Chemistry, and Computer Science. I am interested in working to develop: -more...
  3. ReidMerrill

    Interpreting NiCl2 (dppe) H-NMR Peaks: Chemical Shift Analysis

    Homework Statement I'm trying to interpret an H-NMR of NiCl2 (dppe) and am trying to match the peaks in the aromatic region. Homework Equations 3. The Attempt at a Solution [PLAIN]http://[URL=http://s350.photobucket.com/user/remerril/media/hnmr_zpseljx6e8x.png.html] I think that the...
  4. RicardoMP

    I Sommerfeld Expansion & Chemical Potential

    Hi! I'm trying to show how the chemical potential depends on the temperature and I'm advised to use the Sommerfeld expansion. I'm using it on the density of charge n=\int^{+\infty}_{-\infty} \rho(\epsilon)n_Fd\epsilon , which gives n=\int^{\mu}_{0} \rho(\epsilon)d\epsilon...
  5. cliffordlim

    How Do You Calculate Equilibrium Concentrations in a Redox Reaction?

    Homework Statement Fe2+and Cr2O72- react as follows: 6Fe2+ + Cr2O7 2− + 14H + >>> 6Fe3+ + 2Cr3+ + 7H2O. The equilibrium constant for the reaction is 1×10^57. Calculate the equilibrium concentrations of the iron and chromium species if 10 mL each of 0.02M K2Cr2O7 in 1.14M HCl and 0.12M FeSO4...
  6. M

    Programs Is engineering in chemical biology right for me?

    It's basically a program where chemistry overlaps all aspects of biology. I am interested in understanding biological systems from the perspective of chemistry, and I would like to apply this knowledge to different areas of biology/chemistry such as synthethic biology, protein development and...
  7. G

    Looking for a website that suggests chemical equations

    I'm looking for a website that suggests chemical equations based on a single reactant and product. For example if I have C2H4 as a reactant and C2H3Cl as a product, I should get 1. C2H4 + Cl2 --> C2H3Cl + HCl 2. C2H4 + Cl2 --> C2H4Cl2 C2H4Cl2 --> C2H3Cl + HCl
  8. F

    Chemical Bonds - various questions

    A group 2 metal always forms 2+ ions, since the second electron is harder to remove how come you don't find 1+ ions of these in ionic compound formations, How does it always manage to lose both outer electrons? So it takes a certain amount of energy to break a bond, how does water molecules...
  9. A

    Temperature physical or chemical change

    If you Increase or decrease temperature and change states of matter, that's a physical change. But are there any circumstances where temperature can cause a chemical change? Like if increasing temperature could break the bonds between the atoms and separate them? And I don't mean a combustion...
  10. physea

    Role of pressure and temperature in chemical reactions

    Hello! I have a feeling and I would like to know if it is true. I feel that if a reaction between two gases, takes place in high temperature only (perhaps with the presence of a catalyst), then if we increase the pressure high enough and keep the temperature low, the reaction may still take...
  11. D

    Determine Enthelpy, Entropy, and Chemical Potential

    Homework Statement Hello, i am given an isothermal transition for nitrogen, N2, where temperature is constant at 700K, p1=1bar, and p2=100bar. For this problem i am not allowed to use any equations of states, such as Benedict-Webb-Rubin, or Beattie-Bridgeman. Rather i am given only Cp data...
  12. N

    MHB Chemistry: Demonstrate the definition with a chemical equation for HCl.

    Demonstrate the definition with a chemical equation for HCl. Express your answer as a chemical equation. Identify all of the phases in your answer. My Answer: HCl(g)+H2O(l)→H3O+(l)+Cl−(aq)What the answer said: There is an error in your submission. Make sure you have formatted it properly.
  13. B

    What if a chemical reagent reports purity as a range?

    I have a chemical reagent that says: Assay ... 93.0 ~ 103.0% Which value should I use in theoretical computations? Should I take the average or the lowest value? Thanks!
  14. BillTre

    I Chemical Life Possible in Brown Drafw Atmospheres?

    Its been proposed that chemical life might exist in the atmospheres of brown draft stars.
  15. 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?
  16. H

    Diffusion down chemical potential gradients

    Ignoring cross-diffusion, diffusive mass fluxes down chemical potential gradients can be described by the equation (I am working from de Groot and Mazur's 1984 text on non-equilibrium thermodynamics): \frac{\partial C_k}{\partial t} = L_{kk}\frac{\partial (\mu_k-\mu_n)}{\partial x} where C_k...
  17. 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...
  18. N

    Is there any chemical reaction with 0 time?

    One that occurs immediatly?
  19. B

    A Primitive cell parameter given chemical unit cell info

    Experimentalists usually provide chemical unit cell information including full symmetry (space group) information of the crystal together with coordinates of independent atoms. But this cannot be directly used by ab initio packages, which requires either primitive cell or unit cell information...
  20. Mayan Fung

    Finding chemical potential with given thermodynamic relation

    Homework Statement Suppose you are given the following relation among the entropy S, volume V , internal energy U, and number of particles N of a thermodynamic system, where A is a constant.: $$ S = A(NVU)^{\frac 1 3} $$ Find the chemical potential μ(T,P) Homework Equations $$ \frac μ T =...
  21. L

    Chemical potential at equlibrium

    What is the value of chemical potential of a substance at equilibrium? According to following article it is zero: https://www.uni-muenster.de/Physik.AP/Demokritov/en/Forschen/Forschungsschwerpunkte/mBECwatfratcp.html But I have seen in many articles that it is the change in chemical potential...
  22. Simon Chen

    A Flexibility and chemical bonding

    Recently, I have been studying flexible thin film transistor (TFT), so I wonder the relationship between flexibility and chemical bonding. Chemical bondings composed of sp3 orbital, s orbital, which one is more flexible? Which one of amorphous Si film, poly Si film, IGZO film is more flexible...
  23. B

    Chemical Separation: Vacuum Distillation Explained

    I don't get what is vacuum distillation anyone can help me with this
  24. D

    Chemical thermodynamics, entropy, Maxwell relation and Z

    Homework Statement A gas obeys the equation of statez=1/(1-b(molar density)) What is the molar entropy change of expanding this gas from a volume of 1 dm3 to 2 dm3 at a temperature of 300 K, given b = 0.2 dm3? Calculate your answer to three significant figures and select one answer from the...
  25. 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?
  26. Recycler

    Chemical treatment of silicon carbide

    I modified an employer's patented device,in order to treat bulk silicon carbide grit.It became crystal clear resembling clear silica grainsThe resultant was not analyzed.This was a low-temperature process.Is there any potential application for this type of process?
  27. T

    A Predicting Fermi Surface from Chemical Formula

    Hi, I was hoping I could get some things cleared up. Recently my Solid State professor mentioned that we could simply, from the chemical formula, predict where the band crossings are going to be. For example, take LaFeAsO. Since La has a valency of +3, Fe of +3, As of -3, and O of -2, he...
  28. 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...
  29. Liam A

    Chemical Composition of Paper: Structure & Molecules

    what is the chemical composition of common processed paper and what does the molecule's structure look like?
  30. I

    Are chemical messages between proteins intermolecular forces

    This question might be a stretch, but I was just reading about inter- and intra-molecular forces. And I found that "Intermolecular forces (IMFs) are forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions)"...
  31. iTryToLearn

    Give the chemical formulas for four possible salts

    Lets say you were given an unknown which contains two salts, and your results give you evidence that potassium phosphate, ammonium, and carbonate ions are all present. What are four possible salts that could be your unknown?
  32. Karan Punjabi

    Understanding Chemical Thermodynamics: Exploring the Concept of State Functions

    Guys I am getting confused that what is state function? People say if state changes then state function also changes. But my view is if that variable changes then only state changes and its not necessary when a state change will always lead to change of every state function.
  33. P

    Chemical Lab Cake: Baking with Substitute Ingredients

    Baking a cake entirely with the chemical lab equivalents of traditional baking ingredients has always been something I've wanted to try. Now, I have the chance (i.e. the time) to do so or, at the very least, figure out how it would be done. I need some help with what would actually be put...
  34. M

    Air chemical analysis "homemade"?

    I have a steelworks nearby my home. Is it possible to perform an air analysis in order to know how much the air is polluted? Which instrument do I need ? Are there cheap possibilities? Thanks a lot in advance for your help!
  35. V

    A Question about Chemical Equilibrium

    say we have a reaction: N2O4 <====> 2NO2 for this reaction,if initial number of moles of N2O4 is 'a' can we write t = 0 a - at equilbrium a-x...
  36. 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...
  37. A

    Balancing chemical equations polystomics and H2O + CO2/NO2

    Homework Statement (NH4)2S + HNO3 = ? - main problem LiHCO3 + HClO = ? - check just in case problem Homework Equations None. The Attempt at a Solution I think it has to equal H2S + NH4NO3 Or H2S + NO2 + H2O I've used multiple online chemical balancing calculators and they all give me...
  38. thebosonbreaker

    What does this symbol mean in a chemical equation?

    I recently stumbled across a chemical equation, which had a symbol I have never seen before. If anyone can tell me what this symbol means, I would be very grateful. Here's the equation: Ca(OH)2(aq) + Na2CO3(s) → CaCO3 ↓ + 2 NaOH(aq) ...and I'd like to know what the "↓" symbol means. Many...
  39. S

    Programs BSc Chemistry to MSc Chemical Engineering?

    I was just hoping for a bit of feedback on how realistic of a transition this would be. I'm nearing the end of an honors degree in chemistry and the job prospects look a bit dire. In my area there are lab technician jobs that require the applicant to have a degree, and the pay is less than what...
  40. S

    Engineering Chemistry vs chemical engineering in MS and PhD

    I used to be a chemical engineer for a bad company that treats its employees very poorly. Ever since leaving that place, I've been trying to transition into the tech industry, because it's where all the new, and exciting stuff happens. I'm particularly interested in battery technology, because I...
  41. 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...
  42. S

    Entropy vs. enthelpy in chemical reactions.

    Hello, I am learning about using Free energy change /delta G to determine if a chemical reaction will occur spontaneously. /delta G = /delta H + T*/delta S. Now, enthalpy change can drive a reaction which leads to a decrease in entropy (multiple reactants => single product). My Question...
  43. Einj

    Euclidean correlators for finite chemical potential

    Hello everyone, my question is about Euclidean correlators (say a 2-pt function to be specific) in presence of non-zero chemical potential. The question in particular is: is it still true that the Minkowski time ordered 2-pt function can be simply obtained from the Euclidean one by analytic...
  44. L

    Chemical Eng: How do I get value M from 2 unknown variables.

    Homework Statement At T1 the root mean square speed (rms) of compound P is 485.2 m s-1 and at T2 the rms speed is 504.1 m s-1. Using this data and the fact that T2 – T1 = 24.0 °C, determine the molar mass of P in g mol-1. Homework Equations From problem statement you have: (3·R·T1/M)1/2 =...
  45. P

    Chemical or Electrical engineering

    hi guys, i am in a bad situation and i need some tips :( i attend the first year of chemical engineering, but i have doubts about my choice... My university gives me the way to change my course in electrical engineering, and i am thinking to change. I'm not sure that chemical engineering is a...
  46. 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...
  47. K

    Chemical Kinetics: Understanding the Reaction of A & B

    Homework Statement The task is the following: If the concentration of A decreases 0.03 M in one hour, then the concentration of B should to, which means, [ B] should be 0.05 M? And if I try to calculate k, i get 14.87 l/(mol*h) For second order reactions, t1/2 sould be 1/(k*[A]0) So I get...
  48. S

    Chemical PCP found in older Electrical Transformers

    I worked for the Public Utilities company last summer, and we were tasked with taking inventory around the entire city, of all the transformers. We wrote down as much info as we could about the transformers, including Serial Number and whether or not it contained PCP's. From what I understood...
  49. B

    B Chemical composition of relativistic neutron star jets?

    Is there any good information about the chemical composition of relativistic jets from neutron stars? If the chemical composition of the jets was different from the accretion material it could shed light on the process that forms the jets.
  50. Creaver

    Eurosciences junior chemical element question

    Hello, Imagine a chemical element of the periodic classification with 2046 as atomic number. The highest physicists will tell you that such an element is totally unstable. It prevents not at all the rule of Klechkowski from applying to the atom of this element.. Would you know how to give me...
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