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. M

    Is Detonation a Physical or Chemical Reaction?

    1.The explosion resulting from the detonation of High explosives likes TNT ,RDX ...are they chemical reactions at all ,because the initiation requires detonation waves and no flame or oxidation as such . 2.Detonation is followed by rapid expansion of gases accompanied by shockwaves ...
  2. W

    What is the Chemical Formula of Diesel?

    Homework Statement For a assessment task at school, I have to compare various types of fuel, one of which is diesel. One aspect of the task is to name the chemical formula for each fuel. The Attempt at a Solution I keep finding that the formula for diesel is C12H23. I know that diesel is...
  3. K

    Saturation chemical potential- what is it?

    hi there first excuse me for my poor english! can anyone explane what the hell is the 'saturation chemical potential'?! and how can i get it? thanks guys
  4. A

    Research Advice for a Chemical Engineer

    Is there anyway I can satisfy my thirst for discovering something about nature (anything as long as it raw origins from nature, a fluid counts; regardless of its real-world applications) by researching or pursuing a phd in ChemE for instance integrating it with its 'physics-based' roots. It...
  5. P

    Help on precise definition of chemical potential T->0 FD Distribution

    Hello everyone, first post here. In trying to decipher the meaning of chemical potential, I feel as if at least in the context of the Fermi-Dirac Distribution I have almost nailed it down. As I understand it, the chemical potential is the change in energy associated with the addition of one...
  6. D

    Do chemical properties have an effect on gravitational forces?

    Do gravitational forces discriminate against chemical energy potential? Could the gravitational forces of three substances, equal in density, but differing in chemical properties affect each other differently based on their differences in chemical energy potential? Take two separate bodies of...
  7. N

    Question about chemical engineering specialties -> future

    I love chemistry and math (have taken through calc 3). I was planning on working in the energy field after I graduate, but I have an honest question: does it utilize electricity and magentism? I, frankly, hated that class. I LOVED physics I, which was much more applicable to me. Should I...
  8. D

    Can Mixing Different pH Indicators Broaden Detection Range in Spectrophotometry?

    As an experiment I was going to investigate the use of a spectrophotometre as a pH meter by using different chemical indicators which should change colour depending upon the pH of the substance. I know that indicators such as bromthymol blue only experience a distict change in colour over a pH...
  9. G

    Free energy and Chemical Energy question

    \DeltaG = -n F Emax and \DeltaG = \DeltaG\circ + RT ln(Q) When do we use the first equation and when do we use the second one?
  10. J

    Understanding Chemical Bonding Force - Help John Understand!

    Chemical bonding force. Help me understand how chemists describe this force! So one proton has a positive charge. One electron has a negative charge. When we bring them together, that makes one hydrogen atom. The positive proton and the negative electron cancel each other out. Perfect! But...
  11. A

    How does Helicase unwind the dna strands?what is the chemical Process

    how does Helicase unwind the dna strands?what is the chemical Process involved?what is the chemical reaction?
  12. D

    Odd formula for calculating chemical potential

    Hi all, I've been looking through some code for semi-classical transport characteristics of solids and one of the features it can do is artificially "dope" the system by adding in charge carriers. However it seems a bit unstable so I had a peek to see what they actually did to change the...
  13. R

    Searching for chemical to apply to hair

    Hi, We sell hair products; both synthetic and human hair. Sometimes the customer will cut the hair and then say the hair was too short and request a refund, discount or exchange. We are searching for a safe chemical that we can apply to the ends of the hair so we know if the customer has cut...
  14. entropy1

    Speed of light and chemical properties

    If the speed of light were (slightly) different, how would that affect the chemical properties of atoms, if so?
  15. M

    Chemical Photoshop for Emulating Film and 100 year old processes

    Autochrome is a photography technique which all details forgotten 50 years ago but counted as the best color photograph technique. There are two layers on glass , one RGB Screen and second , a bw emulsion. When RGB filter separates the image , bw all color sensitive layer records the tones...
  16. P

    Chemical Equilibrium and Concentration

    The reaction between hydrogen and fluorine has an equilibrium constant of 1.15x102 at a certain temperature. Given the reaction equation H2(g) + F2(g) -> 2HF(g), calculate the equilibrium concentration of HF after 3.00 mol of each component is added to a 1.500 L flask. I attempted solving it...
  17. Saitama

    Chemical Equivalence: Learn the Concept Easily

    Hello everyone! I am not able to understand Chemical Equivalence? The bookish language is very hard to understand... If someone could explain me the Concept Of Equilvalence, it would be very helpful for me... Thanks, Pranav
  18. QuarkCharmer

    Chemical Formulas from percents/ratios

    Homework Statement 1.) A compound containing only C, H, and O, is subjected to elemental analysis. Upon completion of the combustion, a .4266g sample of the compound produces .5518g of CO_2, and .2259g of H_2O. What is the empirical formula of the compound? 2.) Maleic Acid contains 41.4%...
  19. M

    Can someone identify this chemical compound

    I am unable to identify it.
  20. F

    What really is Chemical engineering? and what can you DO with it?

    I am contemplating between being majoring as a Chemist or a chemical engineer-- and just can't decide. chemistry is initially what attracts me. However-- the APPLICATION of chemistry to a PROBLEM is REALLY what gets me excited, which is what essentially is the definition of an engineer...
  21. K

    Is Our Chemical Knowledge Truly Infinite?

    I'm interested in philosophers' opinions on a question that I posed in another forum (https://www.physicsforums.com/showthread.php?t=496119). As I say in my latest post, the entire thread was sparked by the comments of the Philosopher of Chemistry, Joachim Schummer: We have no reason at...
  22. B

    Chemical Thermodynamics: CO2 dissolves in water, find molality and pH.

    Homework Statement When carbon dioxide "dissolves" in water, essentially all of it reacts to form carbonic acid, H2CO3: CO2(s) + H2O(l) <--> H2CO3(aq). The carbonic acid can then dissociate into H+ and bicarbonate ions, H2CO3(aq) <--> H+(aq) + HCO3-(aq). Consider a body of otherwise pure...
  23. I

    Anyone over 30 start Chemical Engineering program?

    I'm considering leaving my job and enrolling in the chemical engineering program at University of Waterloo. I'm in my early 30's and employed in a Senior I.S. position. I don't have any formal post high school education. Mostly programming and database courses. My wife is going to support us...
  24. A

    Reciprocating chemical reaction is it possible?

    i've got thoughts about a series of chemical reactions that would simply keep on repeating. perhaps by time release. the thought is to use this perpetual chemical reaction to create a battery that releases the electrons then has a series of chemical reactions eventually resulting in the two...
  25. K

    Engineering Chemical Engineering: Pros & Cons to Consider

    I really enjoy chemistry and maths and am considering chemical engineering in uni. I am not sure whether to do chemical engineering degree straight up or chemical engineering/commerce double degree. What are advantages and disadvantages?
  26. K

    Are There Physical Phenomena That Cannot Be Quantized?

    I have been advised that the questions that I ask in another thread in the Chemistry Forum may be better assessed by those who frequent the General Physics Forum. I would be much obliged if you could take a look at the following link, and provide any thoughts, feedback, ideas that you may...
  27. K

    Is Chemical Knowledge Truly Infinite?

    If this is the wrong place for these sorts of musings, I greatly apologize and I would be profoundly obliged if someone could point me in the right direction. Otherwise, on with the question. I have repeatedly heard it said that the number of chemical species and, by extension, the...
  28. F

    Solving Confusion: Ashcroft & Electrochemical/Chemical Potential

    Hello. There is no agreement on the meaning of terms electrochemical potential and chemical potential (see for example http://web.mit.edu/6.730/www/ST04/Lectures/Lecture26.pdf"). While proper definitions would call chemical potential to \mu\equiv\left(\frac{\partial U}{\partial...
  29. D

    Why Are Chemical Bonds More Stable at Cooler Temperatures?

    Homework Statement I was wondering why bonds are more stable at cooler temperatures than at higher temperatures. This question came from a research project about annealing (heating then colling) plastics and why polyethylene maintains its shape when it's cooled.
  30. Y

    Question about chemical nomenclature

    I want to know why there are cis- and trans form of 1,3dibromo-1,3-dimethylcyclobutane? and anybody explain it to me thanks a lot
  31. W

    General Engineering or Chemical?

    So the University of Queensland offers an optional first year general engineering program; at which point you choose a specialization. Alternatively, I think I can just jump straight into Chemical Engineering, which I'm pretty sure is the one i want. I can't know for sure until i get some...
  32. C

    Questions Regarding Chemical Engineering

    Hey there, I am currently a second year chemical engineering student, and was wondering for those of you who are chemical engineers or have studied chemical engineering, what do you currently do? It seems like a very interesting field, and I have been doing quite well in my classes, but I...
  33. S

    Probably getting a C in Calc 2. Can I still become a chemical engineer?

    I am really starting to doubt myself, which sucks because it's what I want to do. Should I retake? Can I move on and be ok? (I did fine in the integrating part, but not so much in series/sequences)
  34. S

    Enantiomer / Diastereomer Chemical and Physical Properties

    Alright so I know the common answer: Enantiomers - same chemical and physical properties Diastereomers - different chemical and physical properties In lecture, our professor said that enantiomers can have different biological effects. I was confused because, as he had said earlier, they have...
  35. W

    Are Chemical Reactions Quantumly Indeterminate?

    When one atom chemically combines to another atom is it totally determinate? I mean if one atom gradually approaches the other would the reaction occur at exactly the same place or does HUP play a part and give it some randomness? I think there is a known answer to this but I cannot find it...
  36. Shackleford

    Chemical potential of mobile magnetic particles in a magnetic field

    I don't know where the 1/2 comes from in the third image. If I set mu total(up) = mu total up (0), I don't get the 1/2. I'm missing something very simple here. http://i111.photobucket.com/albums/n149/camarolt4z28/IMG_20110325_214532.jpg?t=1301107797...
  37. C

    Chemical potential of an ideal gas

    hi, How can I show that the chemical potential of an ideal gas µ(T,V ) can be given by: \mu(T , V , N )=k_{b}T\left(a+1+ln(\frac{Nv_{0}}{V})\right)
  38. C

    Engineering Should I become a chemical engineer?

    Right now I am in chemical engineering, as a freshman, and am taking my first ChE course which involves material and energy balances. I am right now, on my spring break, still trying to understand the topics because its just not coming to me. I am working problem after problem and I usually keep...
  39. C

    Should I become a chemical engineer?

    Right now I am in chemical engineering, as a freshman, and am taking my first ChE course which involves material and energy balances. I am right now, on my spring break, still trying to understand the topics because its just not coming to me. I am working problem after problem and I usually keep...
  40. 7

    Exothermic chemical reaction materials

    Hi all, I'm looking for two material to produce an exothermic reaction of 180-190 C. I'd prefer the materials to be cheap in larger quantities (think mass production). Safe, other than the heat concerns. Not extremely corrosive, toxic... Easy to clean once combined. Prefer materials that...
  41. U

    Physical Chemistry Q: Do conduction band electrons affect chemical properties?

    Warning: I'm not a practicing chemist. Answers in as-simple-as-possible language (but not oversimplified!) would be greatly appreciated! I'd like to know if the chemical properties of a solid can be affected by conduction band electrons. I assume that, in the majority of cases (and perhaps...
  42. O

    Is There a Faster Method for Balancing Chemical Equations?

    i would like to know if there any Method/way to Balance chemical equations? for example if i got this equation: P2S5+PCl5--->PSCl3 i know how to Balance but is take me a lot time to find the correct factor for Each Molecule. hope you Understand what i mean.:smile: thanks.
  43. S

    Chemical Equation of Redox Reactions

    Homework Statement Please help me in chemical equations of redox reactions. Here are the problems. 1. Mixing potassium dichromate, K2Cr2O7, and sulfuric acid, H2SO4, in a test tube. Then, add hydrogen peroxide, H2O2, drop by drop, shaking the solution after every drop. Add until a change...
  44. S

    Schools Which university should I choose for chemical engineering?

    Hi there people. CUrrently I am in a dilemma. I am applying for a undergraduate program from an institution in my country and they are currently offering me 2 different chemical engineering degrees from 2 different universities which are: 1.)Newcastle University (UK) 2.)Technical University...
  45. N

    Programs Minor for a (chemical) engineer

    I am currently thinking of minoring in math because I really love solving the problems. It's only four extra classes, which would be easily incorporated into my curriculum. I'm also considering physics because it fascinates me. I'm not really enjoying my E&M class, but I did enjoy...
  46. A

    How Much Natural Gas Is Needed to Produce One Tonne of Ammonia?

    Homework Statement Ammonia NH3 is made by the haber process: N2 + 3H2 --> 2NH3 The nitrogen required for this process is obtained from air by using the air to burn natural gas CH4 , thereby removing the oxygen from the air, leaving behind only nitrogen. The hydrogen required is obtained...
  47. S

    Why is the denominator of the ratio possible if the forward rate is 2nd order?

    In my textbook there is an example with the following reaction and rate: C6H6 + 3H2 -> C6H12 Rf = kf[C6H6][H2] Then the the example claims that the ratio of the rate constants is: kf / kr = [C6H12] / ( [H2]3 [C6H6] ) How is the denominator of that ratio possible if the forward...
  48. C

    How does a reaction return to equilibrium?

    Hey guys, I have a question regarding the process by which a reaction returns to equilibrium. If a reaction's reaction quotient is greater than its equilibrium constant, it will shift towards the reactants side of the equation to return to equilibrium. How exactly does this happen? Does...
  49. M

    Chemical Electric CELL with graphite electrodes?

    In normal chemical cells, the electrodes are two different metals so that the more reactive one gives off electrons and create a flow of electrons and hence electricity. [the electrolyte is say NaOH aq or whatever] Just wondering - is it possible to have a chemical cell consisting of: a)...
  50. F

    Chemical Equilibrium and Probability

    I am looking at this equilibrium: H2O + D2O <-> 2DHO (D = Deuterium) I have 2.0 mol of H2O, 1.0 mol of D2O and 2.0 mol of DHO. What are the equilibrium amounts of each of the molecules? What I tried: 6 mol of H, 4 mol of D H2O: P(X=H) & P(Y=H) = 9/25 D2O: P(X=D) & P(Y=D) = 4/25 HDO...
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