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. sergey_le

    Why Did My Reaction Order Deviate in Chemical Kinetics Lab?

    last week i did a chemistry lab. i mixed NaOH 0.03M with equal part of methyl violet and mesured aborbance in a spectrophotometer. then i did the same thing with a 0.05M and methyl violet i did today the graphs and got the k' =-0.1647 for the first solution and k'=-0.4022 for the second...
  2. M

    Chemical Composition of nickel alloy

    I ask the foundry to cast nickel alloys and I took a piece metal to do a chemical test. The element composition of the nickel alloy is Ni 70% Cr 12% Fe 1.2% Mo 2.5%...so far they all are in the allowable range. But I found the alloy also contains W 0.004% ! Is this the normal condition ? ? I...
  3. StanG_80

    Could This Chemical Reaction Have Been Dangerous to Breathe In?

    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
  4. Yeahaight

    Chemistry Is bronze tarnish electrochemical corrosion or chemical corrosion?

    I can't figure it out.
  5. Fig Neutron

    Chemistry Solving pH Changes: Adding Acid to a Buffer or Water

    This is for a high school chemistry class. In part a of the question, I calculated the pH of the solution to be 3.38. Part a was the question: Calculate the pH of a solution containing 0.75 M lactic acid (Ka= 1.4 *10^-4) and 0.25 M sodium lactate. For part b I am having trouble determining how...
  6. QuarkDecay

    B Chemical Potential μ in Solids

    There is the equation: μ= Eu +Eg/2 +3/4kβTln(mu/mc) Eg is the band gap, but I don't understand what Eu stands for and how we can calculate it? Could it be the valence band?
  7. cahill

    I Change in chemical potential energy from nuclear decay

    I have been amateur reading about beta decay. The example given for electron capture was krypton-81 into bromine-81. Going from a noble gas to a halogen gives rise to a big change in chemical potential energy. How is this energy accounted for in the equations of the reactant particles and...
  8. Q

    Switching to chemical engineering from physics?

    Summary:: Would it make sense for me to switch from physics to chemical engineering if I have no interest in most chemical engineering jobs? I’m currently a first-year physics major. Over time, I’ve come to the conclusion that my general interests lie in applied science rather than in pure...
  9. J

    Energy in chemical rocket fuels compared to car fuels

    I am no expert, so forgive me if I sound rather ignorant, but I'm curious about this: are typical automobile fuels like gasoline, diesel and ethanol more energetic than, specifically, *chemical* rocket fuels [like perhaps the types used in missiles, space-bound rockets and such] if measured by...
  10. r12214001

    Chemistry Relationship between chemical equilibrium and rate equilibrium

    Q: Is it true that the value of K depends on the amounts of reactants and products mixed together initially? Explain. A:NO, Equilibrium and rates of reaction (kinetics) are independent of each other. A reaction with a large equilibrium constant value may be a fast reaction or a slow reaction...
  11. 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...
  12. Witcher

    Chemistry How Does Hydrogen Donate a Proton with Only One?

    My question for Bronsted Lowry chemical equation is about the donating and accepting electrons. In the bottom chemical equation, the acid is a proton donor. How can hydrogen donate a proton when it has only 1? Or is the subscript the proton in chemical equations
  13. Adrian Tudini

    Equipment for performing chemical reactions

    Hi I was wondering what equipment is used to measure the actual yield of a chemical reaction when a voltage is applied?Thanks.Adrian
  14. somasimple

    Is the energy equation meaningful without 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.
  15. W

    Chemical Waste Testing: Solutions & Parameters

    Hi Recently my company has wanted to conduct waste testing to determine the composition of the wastes in concentration or wt%. This testing will help us to determine whether there are any excess chemicals in the feed of the process, which in turn can also be used to identify the effective...
  16. Witcher

    Chemistry How can oxidation numbers be used to balance chemical equations?

    I attached my attempt and the question from the book, as you can see i kept failing because my hydrogens wouldn't balance and neither would my oxygens.
  17. 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
  18. 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.
  19. 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...
  20. J

    Programs Graduate Physics after MsC res in Chemical Biology and Bachelor in Biology

    I am 25 and I have graduated from Oxford university in Chemical Biology but strongly believe that I want to do Physics all my future life. I did my Masters by research on the department of Chemistry and I was co-supervised by Professor in Organic Chemistry and Professor in Physical Chemistry. So...
  21. F

    Are nuclear or chemical energy release thermodynamic processes?

    In process of releasing heat of nuclear reaction and burning oil, the internal energy of the material(that be burned) be contant if we prevent heat transfer to environment.The temperature of the material increase.How is entropy of the material varied(if we keep volume be constant)?If the entropy...
  22. Max Kovalevich

    Transform the periodic table of chemical elements.

    Summary: Transform the periodic table of chemical elements (periodic table) into a universal way of storing and transmitting information using spectral analysis. I propose a concept in which the basis for working with information (conservation, transmission in networks) is to use spectral...
  23. J

    Understanding the chemical process in a fuel cell

    Hello, I'm taking an energy class and I'll be giving a presentation on fuel cells. I was wondering if I could get some help understanding the whole process of the paper below. Unfortunately, I can't post the article because of copyrights. To summarize, it's a one compartment H2O2 fuel cell with...
  24. BillTre

    Chemical Element Haikus: Science Magazine Series

    Science magazine, to go with their recent history of the periodic table (I guess), they now have a series of Haiku, one for each element. It is here.
  25. T

    Safe Methanol Substitute: Finding the Right Chemical

    Hi I was wondering if anyone could tell if there is a chemical that reacts the methanol but is also safe to consume in small amounts
  26. cookiemnstr510510

    Programs What Should I Prepare for as a Junior Chemical Engineering Transfer Student?

    Hello All! I am an aspiring chemical engineer. I am currently finishing my sophomore year at community college. I live in California and will be transferring to SJSU, Berkeley or Davis this Fall. I have some questions for chemical engineers, teachers, grad students, or anyone who has more...
  27. A

    The Definition Of Chemical Elements

    I don't get it - the definition of a chemical element is: "Cannot be chemically interconverted or broken down into simpler substances" -- But isn't every atom of an element made up of further sub-atomic particles, and atoms can be then broken apart, etc...? Also, how did people tell the...
  28. W

    Thermal Physics: Fermi Gas and chemical potential

    Hi all, I have an issue trying to understand the following paragraph from Blundell's book. How, exactly, does the definition of ##\mu_0 = E_F## "make sense"? In the sentence after 30.21, it seems to say that the mean energy for a system with ##N## particles differs from that of a system with...
  29. Jirby

    Clear chemical or material that will absorb or deflect IR?

    Hello All, I'm curious if there is some chemical or clear / semi-clear material that will absorb or deflect infra red light in the 890 - 910 nm range. IR absorption would be ideal, but deflection should work as well. The idea is to prevent reflection of IR back to it's source. I hope this...
  30. nineteen

    Chemistry Finding the Chemical Formula and Relative Molecular Mass

    My chemistry teacher gave me this problem. I tried and tried, but I couldn't figure it out and the deadline is tomorrow. Please help me out here friends. 1. This is the problem : In a compound which is made of element Y, weight percentage of Y is 72% and N( Nitrogen) is 28%. Also, 3 Y atoms...
  31. 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...
  32. R

    Chemical structure vs excitation frequency (photons)

    Is there a text, or set of texts, on how to predict what frequency of photon is released when a particular molecule is brought to an excited state and then relaxes? So for example if you were to put, say, benzene into an electrical tube and excite it what frequency would be released and more...
  33. J

    I Ab Initio methods for chemical reactions?

    Well, I know this is not the "Chemistry" subforum but the question is all about quantum physics. When you study the Schrödinger equation you can compute the time evolution of the wave function, see what energy levels are possible etc. You can calculate the spectra of atoms describing them as a...
  34. M

    Help with Chemical reactions that make water unstable....

    Directly without any introduction _ I really want some help from chemical engineers I was just looking for some chemical reactions that can make water unstable like when we put it in the water the water will move will not be stable or in an equilibrium state thank you very much
  35. L

    I What is the relation between chemical potential and the number of particles?

    Chemical potential is defined as the change in energy due to change in the number of particles in a system. Let we have a system which is defined by the following Hamiltonian: $$H = -t \sum_i^L c_i^\dagger c_{i+1} + V\sum_i^L n_i n_{i+1} -\mu \sum_i^L n_i$$ where ##c^\dagger (c)## are creation...
  36. 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...
  37. J

    Determining if the pH changes when a chemical is added

    Homework Statement The question asks, how many of the following statements is/ are correct. I want to know which ones are right (I don't know the answer, but I will give a guess). BaCl2 added to an HCL solution does not change the pH NaBr added to an HBr solution will raise the pH. NaC2H3O2...
  38. jfizzix

    I Are no chemical elements truly stable?

    I recently learned that Bismuth is actually radioactive with its longest lived isotope having a half-life of about 20 quintillion years. (For source, see: https://www.nature.com/articles/nature01541) As a very basic question, what determines whether an element/isotope will be radioactive? Is...
  39. 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...
  40. M

    Chemical Industry Data: Sources for Production & Prices

    I am curious about production amounts and prices for an annual period, for a few thousand commodity or common chemicals. I noticed a couple chemical intelligence services but they seem out of the price range for an amateur researcher. What kinds of sources are available to look further?
  41. steroidjunkie

    Semiconductor chemical potential and the density of holes

    Homework Statement [a) Show that chemical potential in intrinsic semiconductor at T = 0 lies exactly in the middle of the energy gap. At what temperature is the chemical potential equal ##(3/4)(E_c + E_v)##, where ##E_c## and ##E_v## are energies od the bottom of the conduction band and of the...
  42. R

    Portable chemical sensing technology

    I'm curious about what sort of technology is used for portable chemical sensing and how expensive or portable it is. For instance, I've occasionally been pulled aside by airport security, and they took a swab, wiped it on some piece of luggage and then as I recall (I didn't pay close attention)...
  43. navneet9431

    Does the Potential Energy increase during Chemical Bonding?

    Hi All, The Potential Energy for two chemically bonding atoms is defined by ,U=1/2(k*q1*q2)/r So it means that when the atoms approach each other then, their Potential Energy will increase. Where am I doing wrong? I will be thankful for help!
  44. davenn

    Difference - chemical formula and Idealised chemical formula

    Hi guys I'm into rocks and minerals but I'm not a chemist I can't really find a definition between ... chemical formula and Idealised chemical formula ? example below of a mineral sample I purchased a few days ago part info from ... https://www.mindat.org/min-3760.html Chemical Properties of...
  45. P

    Chemical bonding during touching

    there is some chemical bond between the skin of one person and another during touching?
  46. 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?
  47. R

    Chemical Vapor Deposition - Diamond

    Are there any instructional video's on how to make your own CVD Diamond optics. I was looking online and CVD Diamond wafers are EXTREMELY expensive. Is it possible to make a plasma chamber for CVD if so does anyone have any good text recommendations What is the catch
  48. N

    I Chemical Bonding - Wave function

    https://ps.uci.edu/~cyu/p224/LectureNotes/lecture7/lecture7html/ Does NaCl have a wavefunction? If so, is it entangled?
  49. P

    I Chemical potential on a solid and its vapor pressure

    I have been reading the book "Nanostructures and Nanomaterials" by G. Cao and Y. Yang, and was intrigued by the following passage in page 33: "Assuming the vapor of solid phase obeys the ideal gas law, for the flat surface one can easily arrive at: μv − μ∞ = −kTlnP∞, where μv is the chemical...
  50. M

    How are the isomers of tris(acetylacetonato) chromium(III)?

    Homework Statement How to draw it? Can someone tell me the electronic configuration of the chromium atom in tris( acetylaceato)chromium( III) please Homework Equations N/A The Attempt at a Solution N/A
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