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. C

    Chemical Computers: Designing Glucose-Based Computers

    Is it possible to use simple glucose to design a chemical computer, and therefore reflect the architecture and chemicals of the human brain?
  2. Rahulx084

    Understanding Reactor Balancing: Flow Rate and Volume Relationship

    I'm confused in the balancing of a reactor , let's say the inlet volumetric flow rate is ##v_○## and outlet volumetric flow rate is ##v_1## Doubts: 1) How is the volumetric flow rate and volume of the reactor ##V## are related to each other ? 2) If the volumetric flow rate is constant (...
  3. amjad-sh

    A What is the significance of spin chemical potential in physics?

    Can somebody give me some insights related to spin chemical potential ? I searched on google but didn't get satisfied. What it means when two spin groups of electrons (group A with spin up and group B with spin down)have different spin chemical potential?
  4. S

    How Does Increased Pressure Affect Chemical Equilibrium in the Reaction A⇔2B?

    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...
  5. 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
  6. 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
  7. 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...
  8. G

    Strange Nucleation Sites Inside a Diet Pepsi Bottle?

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  9. R

    Chemical terminology for an electron in water

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  10. I

    Spontaneous "back-and-forth" chemical reactions

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  11. isukatphysics69

    Change in chemical energy of rocket

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  12. dRic2

    Database for chemical and physical properties

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  13. I

    Chemical reaction vs chemical process

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  14. 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...
  15. I

    Spontaneous uncoded chemical reactions in living systems?

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  16. J

    What's the difference of this chemical formula?

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  17. 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...
  18. S

    Difference between chemical physics and physical chemistry

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  19. somelazyguy

    Chemical Physics to Mathematical Physics -- Early Confusion

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  20. E

    A very strange chemical reaction

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  21. ISamson

    Theoretical interpretation to understand chemical recations

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  22. C

    What Is the Relation of Chemical Potentials in Hydrogen Atom Ionization?

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  23. Pushoam

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

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  24. 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.
  25. K

    What chemical should I use to etch away tin?

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  26. not_a_chemist

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

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  27. ISamson

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

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  28. B

    Physics of a chemical reaction: looking for textbook recs

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  29. D

    Chemical Kinetics: velocity and equilibrium

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  30. A

    Does anyone know of a thermally-stable endothermic reaction?

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  31. L

    Identify 2 Unknown Elements in a Chemical Equation?

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  32. 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...
  33. 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...
  34. 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...
  35. 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...
  36. 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...
  37. 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...
  38. 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?
  39. 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...
  40. 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...
  41. 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...
  42. 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?
  43. 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...
  44. 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?
  45. 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...
  46. 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...
  47. 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?
  48. 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...
  49. 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...
  50. S

    How Can I Find the Names and Hazards of New Chemicals 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??
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