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. S

    Chemical equilibrium vs pressure

    Homework Statement Consider the reaction : A⇔2B (⇔ stands for reversible). 1 mol of A and 2 mol of B are taken in a closed container at equilibrium. Suppose the pressure is increased, how much of B (by moles) will decompose to restore equilibrium ? Homework EquationsThe Attempt at a Solution...
  2. DaTario

    I Chemical Elements produced inside the Sun

    Hi All, I would like to know if the following statement is true or false: The nuclear processes that happen inside the Sun can produce at least one unity of each of the known chemical elements. Best Regards, DaTario
  3. dRic2

    Change of P and T after a chemical reaction

    If I have a chemical reaction in closed system, how can I evaluate the change in T and P? I have: - one equation for the chemical equilibrium - one equation for the energy balance but I need an other one! entropy balance, maybe? Thanks Ric
  4. H

    How to write balanced chemical reaction?

    Hi! I've got this problem: 1,20 g of NaHSO4 is dissolved in water to 1,0 liters and pH=2,194. What is the acid dissociation constant for HSO-4? I assume I have to start with writing the balanced reaction, but I don't get how I do that. I know that I'm supposted to start with NaHSO4 + H2O , but...
  5. G

    Strange Nucleation Sites Inside a Diet Pepsi Bottle?

    I have found some odd Nucleation points that appear inside of the top area of a bottle of Diet Pepsi (the area right near the cap as shown in pictures below). The nucleation sites appear either as soon as you open the bottle, or after the first drink (I will test this once more and see exactly...
  6. R

    Chemical terminology for an electron in water

    I've read several papers that talk about electrons in water, clearly they don't last very long as they react quickly with the oxygen. But I'm confused about the terminology they use, some call them solvated electrons, some hydrated electrons and others aquated electrons. I can't seem to find a...
  7. I

    Spontaneous "back-and-forth" chemical reactions

    I was wondering if there is a good example of a chemical reaction cascade that reverses itself, or does a "loop" in nature outside of life? First thing that came to mind was water evaporating and coming back down from clouds, but that is not really a chemical reaction. Or would it be considered...
  8. isukatphysics69

    Change in chemical energy of rocket

    Homework Statement Homework EquationsThe Attempt at a Solution 19800*.35 = 6930J
  9. dRic2

    Database for chemical and physical properties

    Do you know any website where I can find chemical and physical properties of common substance (heat capacity, enthalpy of formation, boiling point ecc...)? Thanks Ric
  10. I

    Chemical reaction vs chemical process

    Hi, I'm hoping to get clear on some chemical nomenclature. A "chemical reaction" is a process that involves some sort of chemical change. But a conformational change doesn't involve a chemical change, just a shape change, thus from what I understand, it cannot be termed a "chemical reaction"...
  11. E

    What is the true meaning of chemical activity in solutions?

    Hello - I am wondering abut the meaning of chemical activity. Most definitions are something along the lines of "effective concentration," which is fine until you have a real concentration in a lab, and you don't know if you need to calculate the concentration or "effective" concentration of the...
  12. I

    Spontaneous uncoded chemical reactions in living systems?

    How easy (or not) is it for spontaneous chemical reactions to occur in a living cell, but particularly reactions that are not a result of and between coded molecules? For example, when we eat food, in the process while the essential molecules are being taken to be integrated into "coded...
  13. J

    What's the difference of this chemical formula?

    Homework Statement I found out that Bauxite has 2 formula, which one is 2Al(OH)3, and the other one is Al2Si2O5(OH)4⋅2H2O. What's the difference of these formula? Homework EquationsThe Attempt at a Solution
  14. C

    Why is activity of solvated components equal to 1?

    Homework Statement Consider the following reaction $$\mathrm{Ni^{2+}_{(aq)} + H_2S_{(g)} \to Ni_{(s)} + S_{(s)} + 2H^{+}_{(aq)}}$$ What are the activities of the terms in the reaction? Homework Equations The activity is defined as ##a = c/c^\circ## in ##\mathrm{ mol \, dm^3}## 3. The...
  15. S

    Difference between chemical physics and physical chemistry

    What is the difference between physical chemistry and chemical physics?
  16. somelazyguy

    Chemical Physics to Mathematical Physics -- Early Confusion

    Hey. Undergrad UK Chemical Physics student here. Looking for some advice when it comes to sorting out my degree path. First however. Some background info for those unaware with the degree 'system' in the United Kingdom: Most Universities in the UK have you apply for degree programs through...
  17. E

    A very strange chemical reaction

    This is probably the weirdest chemical reaction you'll ever see.
  18. ISamson

    Theoretical interpretation to understand chemical recations

    Isn't this a breakthrough? Well, a base for a breakthrough? I have always wondered if a complete theory or accurate prediction of the formation of bonds and molecules is possible... I tried to think about this myself... :) What do you think...
  19. C

    Find the relation of chemical potentials in chemical reaction In hydrogen atom ionization

    Homework Statement In hydrogen atom ionization H→p+e show that ##μ_H=μ_p+μ_r## Homework Equations G=μN (N is the number of particles) The Attempt at a Solution (1) I think the question should say "Find chemical potential relation AT EQUILIBRIUM", don't you think? (2) My professor said that...
  20. Pushoam

    Relation between chemical potential and S,V,T,P

    Homework Statement Homework EquationsThe Attempt at a SolutionChemical potential is defined as ## \mu = Gibbs potential per particle ##. So, is the system consists of N particles, ##\mu = \frac { G } {N } ##. Now, dG = VdP – SdT ## \frac {dG } { N } = \frac { VdP } { N } - \frac { SdT }...
  21. F

    Standard chemical potential and activity of asphaltene

    Hi , this is my equation : μA= μA0 + RTlnaA A is the asphaltene in toluene solution . i want to calculate μA in different temperatures. where can i get μA0 and aA? tables? other equations? μA0 is the standard chemical potential of asphaltene and aA is the asphaltene activity in solution.
  22. K

    What chemical should I use to etch away tin?

    I am having difficulty in finding a solution that can etch away tin compounds in my metallic surface. The metallic surface has a composition of palladium, copper, and silver. There is a tin compound deposited on the surface which I would like to etch away or remove. This is on a microscopic...
  23. not_a_chemist

    Chemical Polymer Separation (PLA, ABS, HIPS, and PETG)

    Good day all! I've got a granular mixture of PLA, ABS, HIPS, and PETG with a particle size of about a quarter inch, and I'm trying to isolate each polymer from the mix. PLA and PETG have densities of about 1.27g/ml, and ABS and HIPS have densities of around 1.06g/ml. I think a weighted solution...
  24. ISamson

    B Chemical study of an old, metal-rich globular cluster

    Regarding a recent article from phys.org , Chilean researchers have conducted a study of an old, metal-rich cluster, NGC 5927. Interesting results are the abundance of many metals, which include sodium, aluminium, iron, oxygen and some heavy metals such as yttrium and zirconium. Thank you.
  25. B

    Physics of a chemical reaction: looking for textbook recs

    I'm currently doing a literature review on ultracold chemistry with an emphasis on collisional theory and quantum phenomena. I'm an undergraduate physics major, and I'd start my discussion of this topic by moving from basic Newtonian conservation laws and concepts like Coulomb repulsion to the...
  26. D

    Chemical Kinetics: velocity and equilibrium

    Hi everybody, Given a generic reaction ## Reagents ↔ Products ## the velocity of the reaction is ##R = R_{right} - R_{left} ## To take in account that the velocity of the reaction will slow if approaching the equilibrium we say that $$ R = R_{right}(1 - \frac K K_{eq}) $$ Although it seems...
  27. A

    Does anyone know of a thermally-stable endothermic reaction?

    Hello all, I've used physicsforums a few times over the years, but I believe this is my first post. I'm working on an engineering project in which I need to find a highly-endothermic reaction where the reactants and products will be stable at very high temperatures (well over 800C), or at least...
  28. L

    Identify 2 Unknown Elements in a Chemical Equation?

    Homework Statement A silly sample of a metallic element M, reacts completely with 0.0237 mols of X2 to form 6.78 g MX. What are the identities of M and X? Homework Equations mols = grams/molar mass[/B]The Attempt at a Solution (kinda have no clue what to do because I'm not sure what to do...
  29. V

    B Can Fermions Exhibit Negative Chemical Potential Like Bosons?

    Is possible and what does it mean if a chemical potential is negative? I mean that for boson it means that in environment is "needed" boson (photon) and is possible to create him. Is it true? And what about for fermions? Could it mean that it is pleasent for environment to creat some fermion? Or...
  30. S

    Ejecting chemical species from a sample using an electron beam

    Hello, I was wondering if it would be possible to eject chemical compounds from a sample, say like a biological tissue, using an electron beam. I know that electron scattering is one product of electron-specimen interaction, and that's the principle behind electron microscopy, but I'm more...
  31. W

    Thermodynamic Identity: Chemical Potential

    Homework Statement Homework Equations Thermodynamic Identity The Attempt at a Solution While I was able to work out the problem with the help of the hint, I couldn't completely understand the implication of said hint. The hint suggests that the equations for Chemical Potential in a process...
  32. C

    I am writing a story involving a hypothetical chemical reaction

    Hello, this is my first posting on this forum. I enjoyed Chemistry in high school, though the arts were where my abilities drew me. I've learned that a ratio of 2 hydrogen to 1 oxygen, when ignited by a certain amount of heat, will create a small amount of water. I will give a brief outline on...
  33. labentzel

    Programs Chemical Engineering vs. Electrical Engineering Major

    Hello everyone! I'm currently a student about to get my AA degree at the end of the semester so the time has come for me to transfer from community college to university and, most importantly, decide on a major. Throughout my college career thus far, I've bounced around with ideas like...
  34. ISamson

    Spectrum of Chemical with a Glass Prism

    Hello, I was wondering if it is possible to make a definite clear spectrum of a chemical using a glass prism. I have one at home and no matter how hard I try to get an emission or absorption spectrum, it just does not turn out. Can you help? Do I need to focus the light into one point or such...
  35. curiosity colour

    Chemical Equilibrium Q: How Does Solution (a) Know PH2S=Ammonia?

    I have a question about the solution (a) in this example, how does it know PH2S is the same as ammonia? is there something I've miss?
  36. N

    Installing Chemical Storage Tank: Pressure of Liquid or Gas?

    Hello Forum, I'm looking to install a new chemical storage tank at my site. The tank itself is not rated for vacuum. We will have proper ventilation and nitrogen pumping into the tank to compensate when we are pumping out of the bottom. However, I do want to include a pressure transmitter on...
  37. D

    I Gibbs Energy and chemical equilibrium

    Hi, i'll apologize for my english in advance, so here's the question. I was wondering about the equilibrium condition for a chemical reaction. We know that a closed system is in equilibrium if the Gibbs free energy's function has a minimun in that point. So, taking Temperature and Pressure as...
  38. U

    I Why is first TD law different for chemical reactors

    I've learned that first thermodynamic law for some open system is in the form of: where total change of system energy ##\frac{\partial E}{\partial \tau }## is equal to the transferred heat and work. Total change of system energy ##\frac{\partial E}{\partial \tau }## is equal to the energy...
  39. yrjosmiel

    Why do chemical reactions release energy?

    If I have a container filled with oxygen and hydrogen and heat it up, it would react and create water and heat. Why was heat released? What happens in chemical reactions at a microscopic level that makes it release energy in the form of heat?
  40. Shakattack12

    Physical and Chemical Properties of Flagpoles

    Hey guys, Can anyone help me think of some relevant physical (8 or so) and chemical properties (5ish) required by flag poles. I was struggling to think of some but here are some of mine: Physical Flexibility Elasticity Melting point Strength? Electrical conductivity?? Chemical Stability UV...
  41. D

    Why are some chemical powders too expensive?

    I needed to do some experiments, so I was about to buy some chemical products. But it failed because prices were so higher than I expected. The prices got at least double, even triple. Why are some chemical powder products too expensive than bead type?
  42. caters

    Chemical water treatment: Acid base reaction

    I was thinking of a hypothetical waste system that uses nanotechnology to its advantage. At the individual level, waste just passes through into pipes when flushed like it normally does. But once it reaches the water treatment plant there is an initial filter to catch solid waste(in other...
  43. M

    Chemical potential using Boltzmann equation

    Homework Statement I must calculate chemical potential using the Boltzmann equation in relaxation time approximation $$f=f^0-\tau v_z^2 \partial f^0/\partial z,$$ where ##f^0## is given as $$f^0 = 2(\frac{m}{2\pi\hbar})^3 \frac{1}{\exp{\beta(z)(\frac{mv^2}{2}-\mu(z))}+1}$$ I have to consider...
  44. G

    Software to simulate an atom and chemical reactions?

    Hi, I am trying to simulate in 3D a bunch of chemical reactions. Some of them are complex and I would like to be able to just spawn the elements and molecules and watch them collide to see what happens. Is their any free software to do this?
  45. C

    Is Chemical Engineering right for me?

    Hello all, So I've finished my first year of classes. Since my school has a credit window for declaring engineering majors, I need to lock in my life-long career decision. I definitely want to stick with engineering, but I was curious if ChemE is the right one for me. From what I've read, the...
  46. herbertpbarreto

    Chemical Reaction Engineering homework

    Homework Statement The decomposition of phosphine 4PH3(g) + P4(g) + 6H2(g) is first-order with respect to phosphine with a rate constant k = 0.0155 s-l at 953 K. If the decomposition occurs in a constant-volume batch reactor at 953 K, calculate, for 40% conversion of PH3, (a) the time...
  47. S

    New chemical created each year

    hey guys, I need help...I have read about many chemicals created in every year..how can I know the list names of new chemicals and their hazards??
  48. 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...
  49. 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...
  50. 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...
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