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. P

    Are These Chemical Reactions Correctly Balanced?

    please check my work... urgent pleasezz 1> ZnCl2 [aq] + 2KNO3 [aq] → Zn(NO3)2[aq] + 2KCl (s) 2> Ca[OH]2 [aq] + 2Na OAc [aq] →Ca(OAc)2[aq] + 2NaOH (s) 3> NiCl2 + 2KOH → Ni(OH)2 [aq]+ 2KCl (s)
  2. J

    Chemical Composition of Slippery Elm Tree Slime

    I was wondering what the chemical composition of the slime from the slippery elm tree (Ulmus rubra) is.
  3. P

    Chemical engineering employment oppurtunities in the pacific northwest?

    I live in seattle, and right now i am heavily considering chemical engineering. I would really love to stay in the seattle area, but I am not sure if i will be able to, as it seems like most of the good chemical engineering jobs are out east. Does anyone know of any chemical engineering...
  4. K

    Vetro paste chemical formula

    i m a student of Chemistry , and i got a university assignment and i need ur kind help in this matter , i need information about a chemical its name is [Vetro Paste 0.23A what is this , its chemical formula , structure , its physical and chemical properties , and its uses , please guide...
  5. S

    Photons and zero chemical potential ?

    Consider a photon gas in equilibrium with a material cavity (something like a furnace). Why exacly the chemical potential of those photons is zero? The usual handwaving argument is 'because photons are easily created and destroyed' whatever that means. Hydrogen and Oxygen are 'easily created...
  6. P

    Chemical potential different for different systems?

    Homework Statement For a given phenomena of macroscopic particles. If we model it using the canonical ensemble then we get a certain chemical potential u. But if we model it using the Grand Canonical system, we get a varying chemcial potential that depends on the average number of particles...
  7. R

    Beginner books on chemical engineering?

    Hello. Does anyone know of some good beginner books on chemical engineering? Anything would be very helpful. Thank you. :shy:
  8. S

    Top Undergrad Engineering (specifically mechanical, electrical, and chemical)

    The top programs AFTER: MIT UC-Berkley Stanford i goofed off my freshman and sophmore years of HS, but have picked it up now, so I'm looking for engineering. I know Vanderbilt stacks up in the top 10, but I'm not sure which other programs are good. If you can, post some of your...
  9. S

    Chemical Formula Hydrate Lab

    We did a lab at our school recently but some of the questions regarding the lab confused me. The data obtained from the lab is here: Determining the Chemical Formula of a Hydrate Purpose Find the molecular formula of the hydrate of Copper (II) Sulfate, CuSO4 x H20. Prediction When the...
  10. S

    Chemical resonance is legitimate and universal

    "Chemical resonance is legitimate and universal" We all know that Lignus Pauling was the creator of both concepts: Hybridization and resonance. VB theory centered its strength over MO theory in the fact that they were able to better explain the chemistry of carbon [organic]. Today...
  11. M

    What Are the Essential Job Roles in a Basic Chemical Plant?

    I have to do a detailed cost analysis of a chemical plants am ok for material units runing etc. costs, but I have to do stafing cost as well but I am stuck with what jobs are on the plant, I'm going to predict approx. 100 staff for the plant as it is already next to another plant which has quite...
  12. N

    Coupled ODE for chemical reaction

    I have a problem.. for a reaction A + B --> C how do i generate 3 coupled differential equations so that i can sole this using MATLAB ? it is given that rate = kAB thnks!
  13. S

    Can someone simply describe the definition of the chemical potential?

    can someone simply describe the definition of the chemical potential?
  14. C

    Higher Chemical Concentration = Higher Temperature of Precipitation. Why?

    If two chemicals are mixed together If I had varying concentrations of the reactant solutions, why is it that the higher concentration mixtures will precipitate at a higher temperature? and lower concentration chemicals will precipitate at a lower temperature?
  15. edward

    Estrogen altering chemical is commonly used in food packaging

    First it was the toxic pet food and now this. This study was done in 2005. Kind of a long time to wait to issue a recall. http://www.sciencedaily.com/releases/2005/12/051203123328.htm This might explain why male fish in the Potomac River and other places are showing up with eggs in...
  16. S

    Higher Chemical Concentration = Higher Temperature of Precipitation. Why?

    If two chemicals are mixed together, say: Na_2SO_4 + CaCl_2 --> 2NaCl + CaSO_4 If I had varying concentrations of the reactant solutions, why is it that the higher concentration mixtures will precipitate at a higher temperature? and lower concentration chemicals will precipitate at a lower...
  17. K

    Why did you become a chemical engineer

    Hello I'm a last year student in chemical engineering at the KUL and I'm having difficulties finding a job. (sounds ridiculous I know) At each interview people ask me why I began my studies as chemical engineer and why I chose chemistry instead of mechanics, electronics, building... I...
  18. M

    - Chemical Equilibrium [Help] -

    Can anyone please help me on these chem equilibrium questions. I just want to make sure if they are correct or not. 1. A chemical system in equilibrium will a. form more products if the the temperature is increased b. have a specific ratio of product to reactant concentrations c. not have...
  19. Z

    Physical or Chemical Changes? Classify These Reactions Without Prefixes!

    This question asks me to classify each of the following as a physical or a chemical change. a. Tarnishing of copper b. Heating sugar to form caramel c. Pouring concentrated nitric acid on a copper coin to form brown fumes d. Evaporating a solution of copper sulfate to dryness (to form...
  20. A

    What are the Uses of Chemical Conversion Coating in the Aerospace Industry?

    Hi, Why is Chemical Conversion Coating done on ducts, fittings in aerospace Industry.
  21. V

    Solving Chemical Reactions Involving Ammonium

    I can not seem to understand what happens when you react ammonium with certain compounds. For example NH3 + Cu(NO3)2 = ?. How am I supposed to do this?
  22. K

    Are all exothermic reactions chemical changes?

    Are all exothermic reactions chemical changes since they release heat?:confused:
  23. L

    Chemical Equilibrium Stresses

    1. Given the equilibrium reaction: N2(g) + O2(g) <---> 2NO(g) deltaH=180kJ mol-1 State the effect of each of the following potential stresses on the system: A) Temperature is decreased B) The pressure of the container is decreased, keeping volume constant C) A catalyst is added D) NO is...
  24. U

    Calculate K_C for N2, H2 System: 10.7M^2, 4.00M^2, 2.67M^2, 1.67M^2

    Homework Statement N_{2(g)}, 0.32M and H_{2(g)}, 0.66M are placed in a reaction vessel. The system reaches equilibrium when [H_{2(g)}] = 0.30M. Calculate K_C a) 10.7M^2 b) 4.00M^2 c) 2.67M^2 d) 1.67M^2 Homework Equations Equilibrium constant formulaThe Attempt at a Solution This is just...
  25. F

    Chemical Reactions - Redox and Acid/Base

    Homework Statement I basically have 4 sets of solutions which I have to write the chemical reactions for. I already figured out the chemical formulas for the reactants, and just need help determining the final products. I know how to balance, and just need help determining the products...
  26. M

    Chemical Compounds = Ionic Bonds?

    From what I gather both ionic and covalent bonds transform all the elements involved into ions. Does that mean every chemical compound that exists consists of ions and not atoms or are there chemical compounds that are made of pure unionized atoms? Also when they speak of ionized water what...
  27. M

    Solving the Mystery of NaOH + H2O Reaction

    I have trouble trying to figure out what happens to this reaction: NaOH(s)+H2O(l)-> my first thought was that maybe nothing happened but then moved on to wondering wether it ionizes. can someone explain to me what happens and maybe why it does?
  28. B

    Chemical Reaction of Baking Soda during electrolysis

    I was wondering if someone could tell me the chemical reaction of Baking Soda during electrolysis. According to wikapedia baking soda is sodium bicarbonate witht he formula NaHCO3. And/or could someone explain how i could figure out te chemical reaction of different items during electrolysis...
  29. F

    Write chemical equations for the action

    Hi guys, I need your help: A white solid V is heated strongly. At a high temperature, V gives off carbon dioxide and changes to a solid W that begins to glow. When water is added to W, it begins to fizz, produces heat and crumbles to a powder X. X dissolves in water to form an...
  30. E

    News Biological and Chemical Warfare

    I'm rather fascinated by chemical and biological warfare. Not only by the immense power behind it but more the specific targeting of our unique physiology, especially sections such acetylcholine and the prevention of its synaptic transmitter functions. << URL removed by berkeman >> The...
  31. E

    What is the chemical name for:

    Oyster Shell? Alcoholic CObalt (II) solution? Any help would be appreciated... can't really find it at wikipedia... if you could find a link of these please post -Adam
  32. Ahmed Abdullah

    Are electron-flow and chemical change inside a dry-cell, separate event?

    We know that the battery itself is a load and electrons flow through it (through the chemical). In a D.C circuit there is always a certain amount of electron-flow within a given time. Let's assume that, the battery used is a dry-cell battery. Now my question is:- Does this electron-flow...
  33. M

    What is this chemical formula of?

    Can someone tell me what this chemical structure is? [PLAIN]ftp://24.58.188.197/d:/download/chemicalstructure.gif[/URL]
  34. K

    Understanding Chemical Equations: A Guide for Beginners

    Hey everyone, I was wondering if someone could help explain to me how you get these chemical equations? Propane: C3H8 + 5O2 --> 3CO2 + 4H2O + energy (heat) Corrosion (rust): 4Fe + 3O2 --> 2FeO3 How does 4 molecules of iron and 3 molecules of oxygen form 2 molecules of iron...
  35. C

    Does anyone know the chemical formula of cheese?

    I'm interested in trying to find this out because I'm wondering if i could artificially make it from school materials...also i want to do a presentation on it tommorow, if i can't find the relevant information I'm going to have to do my presentation on ionisation energy, which is easy, and which...
  36. F

    Silicon & Neon Compound: Formula & Explanation

    If aluminum has a positive 3 charge and chlorine has a negative 1 charge, then the formula becomes AlCl3, because the negative three in chlorine would balance out the positive 3 in aluminum right? So, what about this? Silion has a positive 4 charge. and neon has a neutral charge. What would the...
  37. F

    Chemical Formula-Must Have Help Today

    If aluminum has a positive 3 charge and chlorine has a negative 1 charge, then the formula becomes AlCl3, because the negative three in chlorine would balance out the positive 3 in aluminum right? So, what about this? Silion has a positive 4 charge. and neon has a neutral charge. What would the...
  38. P

    Potassium and Water: Understanding Chemical Equations

    When potassium reacts with water, one product formed is? -this is to help me study for my CHEM test tomorrow
  39. L

    How Do You Calculate ΔH Using Bond Energies for a Chemical Reaction?

    I am not positive if I did this correctly, but I was wondering if someone could check and then, potentially, offer ideas. The question asked to use bond energies and estimate the energy change deltaH (in kJ/mol) for N=N + 2H2 --> H2N-NH2 (that first N=N is triple) I think I just...
  40. K

    Which of the following is a chemical reaction?

    I am confuse here.Here is another question from my test. Which of the following is a chemical reaction? I.A piece of gold is being heated to melt it II.A ball is being blown III.A piece of paper is burnt IV.A piece of sodium is out into a beaker of water A.I and II B.III and IV...
  41. L

    Chemical equilibrium - Which side is the max entropy?

    Which side is the max entropy? P4(s) + 6H2(g) -> 4PH3(g) (delta H = +37 kJ)
  42. H

    Confused about Chemical Q Decay Calculation?

    I have a question Iam stuck on. I was wondering if i did the right calculations. Please let me know: Through decay, Chemical Q loses one-third of its mass every 7 years. Twenty-five years ago, a container of Chemical Q was buried. The EPA has just dug it up and found 1,000 grams...
  43. A

    (thermodynamics) chemical potential

    Why for systems containing several components and phases does it require that the chemical potential of ecah component must be idential in every phase?
  44. L

    Understanding Chemical Reactions: From Mg and O2 to CO2 and H2CO3

    We lit a piece of Mg so the formula is: 2Mg(s) + O2(g) HEAT-- 2MgO(s) We then dissolved this in water so it would then be: MgO(s) + H2O(l) -- Mg(OH)2(l) Next we blew into the solution which made it: CO2(g) + H2O(l) -- H2CO3(l) Is this all correct? Should I have (Aq) after the...
  45. L

    Chemical reactions and stoichiometry

    hello, i hope someone can help me. i have a few questions. The elements sulfur and chlorine react to give disulfur dichloride according to the equation: S8 + 4Cl2 --> 4S2Cl2. There are 0.5987 mol S8. a) How many moles of Cl2 are needed for complete reaction? b) What mass of S2Cl2 in...
  46. Ahmed Abdullah

    How can basic principles be used to predict chemical reactions?

    Hello, I am a A level student. I find difficulties with different chemical reactions. Is there any simple way of predicting chemical reactions. Is there any basic principles that can be followed instead of memorising chemical equations? Different chemical reactions occurs in different...
  47. B

    Repulsive and Attractive Forces that influence chemical bonds?

    Hi! This is a homework question that I'm supposed to answer but that I really do not understand. "Identify two repulsive forces and two attractive forces that influences the formation of chemical bonds between two atoms." I noticed that this question was already posted once at this website but I...
  48. F

    Chemical Equilibrium Questions - Kc, Kp, Qp Calculations

    Hello, I have a few questions about my homework: (it is a rather long post, but I explained my work in detail, so everything is very clear -I hope-). 1) When we have a reaction such as: SO2 (g) + 1/2O2 (g) <=> SO3 (g) and then we have: 2SO2 (g) + O2 (g) <=> 2SO3 (g), we calculate Kc of...
  49. F

    Identifying Intermediates in chemical kinetics

    Hello, I have the following mechanism: NO + NO -> N2O2 and N2O2 + H2 -> N2O + H2O We need to identify intermediates in the mechanism. I have no idea how to do that. In case it helps, here are the answers (not sure they are right, but I think they are) to previous questions in the...
  50. F

    How do I solve these Chemical Kinetics homework problems?

    Hello everyone, I have been working on several exercises for the past several days, and there are some I just can't seem to do. I would appreciate some help! =) 1) We have the following reaction: C2H5Br (alc) + OH(-) (alc) --> C2H5OH (l) + Br(-) The (-) indicates it's an ion. The...
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