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. N

    Chemical physics of water and biological tissue (specifically, food)?

    I was wondering about the effects of water on a cellular level when frozen. From what I know, when the water freezes it expands and it crystallizes. Now, when I get my salmon fresh, I know not to freeze it if possible, because freezing it ruins the texture and goodness of the meat. Also, if...
  2. B

    Why Multiply the Rate Equation by the Coefficient?

    Hi, I am reading about rates of reactions, and I am confused about why we multiply the rate equation of a particular product or reactant by its respective coefficient, only taking the reciprocal of it. Could someone explain to me why this is done? Is it done merely out of convenience?
  3. O

    Any chemical reaction between air and vinegar?

    If I place a glass of white vinegar on the table, and let it make contact with air, Does anyone have any suggestions on what kind of chemical reaction has between air and vinegar? Thanks in advance for any suggestions
  4. B

    Quantum physics underlining the 'magic numbers' in chemical bonding & more.

    a. What do we know about any quantum-physical law, dictating 8 electrons in the outer atomic shell + the other shells' populations, including the 2 electrons in the innermost. Any physical theory behind these numbers, or just an empirical reality ? b. How reacting atoms 'choose' between...
  5. P

    Solving 3.3 mol Fe_{2}O_{3}: 2Fe+Al_{2}O_{3}

    Calculate the amounts requested if 3.3 mol of Fe_{2}O_{3} Fe_{2}O_{3}+2Al\rightarrow2Fe+Al_{2}O_{3} a)Find the moles of aluminum needed b)Find the moles of iron formed c)Find the moles of aluminum oxide formed Not sure how to go about solving any of these the book is terrible and...
  6. E

    Engineering From UK finishing my PhD in Chemical Engineering, want to move to USA

    Hi, I'm from the UK, and I've almost completed my PhD in Chemical Engineering. I'll soon be 25 years old and I've got my sights set on moving to the USA before I get too old. I could use some American advice on the following: 1) How easy will it be to find an employer in the USA willing to...
  7. B

    Help with a chemical equation please

    Hi I'm new on here and a mature student studying geology. We have an assignment (our 5th one) to be in on the 11th jan . I'm in my 1st yr and have not ever studied chemistry unless you count a couple of years around the age of 11 or 12 which was now roughly 28 yrs ago! Anyway I've been trying...
  8. B

    Balancing Chemical Equation for Calcium Bromide and Sodium Phosphate

    [b]1. Homework Statement [/b] Hi, I am trying to write and balance the chemical equation between calcium bromide and sodium phosphate. Homework Equations The Attempt at a Solution 3 CaBr2 + 2 Na3PO4 ----> 2 CaPO4 + 6NaBr That was the final step in my attempts. How do I balance...
  9. K

    Engineering Cultivating a passion for Chemical Engineering?

    Well I just finished my Chem Final for the semester, and regardless of my performance, the past week I've been studying everything from the foundational concepts to broader theories. At the end of it all, I feel that I have a much better grasp on chemistry, which does not seem as hard as...
  10. A

    Describe chemical compounds as CHARGED, POLAR or NONPOLAR

    Ok, I thought the only two options in existence were Polar and Non-polar... and I'm being asked which ones are CHARGED? What does this mean? Example: NH4+ (ammonium), NO3- (nitrate), N2, O2, H2O Thanks!
  11. P

    Chemical Kinetics, finding rate of reaction

    Homework Statement At 25 C a catalyzed solution of formic acid produces 44.6 ml of carbon monoxide gas in 30s. a) Calculate the rate of reaction with respect to CO(g) production. Homework Equations Rate = dC / dT The Attempt at a Solution dC should be expressed in mol/L but I...
  12. R

    How do I measure chemical potential of a gas?

    How can I measure the chemical potential of a gas (not necessarily ideal), using calorimetry alone? I mean, without knowing any equations of state, being able to measure pressure, temperature, volume, and number of particles. Also, I can add a measured amount of heat energy to the gas using a...
  13. W

    Understanding Parentheses in Chemical Formulas

    I was practicing some balancing chemical equations for a chemistry test, and I noticed this: Cu(NO3)2 (numbers are subscripts.) I've never seen parenthesis in a chemical formula before, no clue what it means. Nothing in my textbooks, and I can't really ask the teacher since the test is...
  14. S

    Engineering Electrical vs Chemical Engineering

    Recently, I decided that I am going to do a minor in Computer Engineering (whether it's at Canada or here in Colombia). However, I haven't decided my major. If i win the scholarship in Canada, I would have 2 extra years to choose, but if I stay here in Colombia, I have to choose in May...
  15. T

    Find grams of product using a balanced chemical equation

    Homework Statement 2KClO3 → 2KCl + 3O2 How many grams of potassium chloride are produced if 25 g of potassium chlorate decompose Homework Equations The Attempt at a Solution 25g * (1 mole KClO3/122.45 g KClO3) *(74.45g/ 1 mole KCl) =15.2 g KCl is this right??
  16. J

    Color change Chemical reaction help

    I am working on a project that needs 2 chemicals to react and change colors. The catch is they most likely need to be or come in a powder form, non toxic, and relatively inexpensive. PLEASE HELP!
  17. C

    Chemical kinetics - reaction rate

    Homework Statement 2HCl + Na2S2O3 -> 2NaCl +S + SO2 + H2O Find the order of reaction with respect to S2O32- and H+ volume of 3.0M HCl was held constant at 2ml Homework Equations S2O32- + 2H+ -> S + SO2 + H2O rate = k[Na2S2O3]m[HCl]n (see number 3.) The Attempt at a Solution i just...
  18. R

    Ex of chaos->order circular patterns in liquid chemical reaction

    Does anyone know the experiment where distinct circular patterns appear to emerge in a liquid chemical reaction? This experiment was covered in my thermodynamics class due to its relevance of order emerging from chaos. All I remember about the experiment is that it was not believed at first for...
  19. T

    Chemistry Bonding: Why Are Atoms Bonded?

    Hello I am currently taking a general chem course, and we are studying bonding. I am having trouble understanding why atoms for ex: 2 separate hydrogen atoms have higher energies than a hydrogen molecule. I understand that atoms/ions are always seeking configurations/geometries that will...
  20. H

    Methane Combustion and Chemical Equilibrium

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  21. B

    Effect of Chemical spillage on ecology

    I am preparing my examination on next week. I face a challenge question on the textbook but it does not provide any answers. Can someone help me? Two questions distribute 10 marks for each. How can I answer point by point to get all the marks in this questions. Many thanks! Consider this...
  22. B

    Chemical Engineering vs Nanotechnology Engineering/ Nanoengineering?

    Help me decide, by suggesting differences and weighing pros and cons of each undergraduate program. I'm in frantic need of help here, and all replies would be appreciated :P
  23. J

    P.Chem: Rate of chemical reactions; Half-life

    A second- order reaction of the type A + B -->P was carried out in a solution that was initially 0.075 mol dm^-3 in A and 0.050 mol dm^-3 in B. After 1.0 h the concentration of A had fallen to 0.020 mol dm^-3. a) Calculate the Rate constant. b) Solve for the half- life of each of the reactants...
  24. D

    Subatomically, what causes an atom speed up when it has a chemical bond broken?

    Homework Statement According to the molecular biology book I am reading, when a chemical bond breaks, the energy in the bond is released in the form of heat. which is to say, when a chemical bond breaks the entire atom's speed increases (the atom gains 'heat energy'). But what is...
  25. M

    Writing Chemical Equations, Is It a Gas or Aqueous Solution?

    Hello, I understand that this question may seem rather obvious for some. Nonetheless, it is something that seems to have thrown me off a number of times. When writing chemical equations involving acidic or basic solutions, I know that the acid on the reactant side is written with the state...
  26. A

    How Do Reactor Types and Sizes Vary for Different Chemical Reactions?

    PER - chemical reaction Q: A reactor is needed to convert A to R in a liquid reaction. The stoichiomentry is simply A→R and the rate data is given in the table below (P5.21, Levenspiel 1999). For the reactant concentration to drop from CA0 = 1.3 mol/L to CAf =0.3 mol/L, determine, a)...
  27. itaischles

    Fermi energy (in semiconducors) vs. chemical potential

    Hi all, In the solid state physics course I took a year ago we used the chemical potential μ which appeared inside the fermi-dirac distribution function to describe the energy that above it no electrons resides and below it they all reside as the temperature reaches 0 kelvin. Now, when I...
  28. K

    Would the precipitate be Copper II Chloride in this chemical equation?

    3 CuCl2 + 2Al + HCL →2 AlCl3 + HCL + 3Cu I'm think it's Copper II Chloride because the Copper is a solid, but the solubility rules with the Cl would suggest otherwise. What would be the precipitate here? One other would the net ionic equation have no reaction, since the ions cancel on both...
  29. R

    Engineering What would be more useful for chemical engineering?

    I think I'm going to aim for chemical engineering, I talked to a guy who now works for bp as a petrochemical specialist, he's retired now due to a car accident, and really think that its the sort of career I'd want to do. From what he said its a sort of mix between chemistry, Electrical and...
  30. sankalpmittal

    Chemical equations are becoming my greatest nightmare

    When I was in class 8th or 7th , I used to complete and balance equations by logic. For example : 2Na+2H2O ---> 2NaOH+H2 NaNO3+H2SO4 ---------> HNO3 + NaHSO4 But now , presently when I am 14 years , (about to complete 14 though) and in class 10th , I always come across the equations which...
  31. J

    Chemical Properties of PAN as a Nitrogen Dioxide Reservoir

    I have read in a lot of places the PAN acts as a very good reservoir of nitrogen dioxide. I can't find much information on why though. All I have found is that PAN is thermally unstable and has a very short lifetime at typical tropospheric temperatures, but becomes much more stable at lower...
  32. S

    Is 1L of petrol made from heptane?

    The course book tells us that 1 L of gasoline(heptane) has the density of 790g/L which it says, means that, 1 L of petrolium has a mass of 790g. At this point i made the assumption that 1L of petrolium has a 790g of heptane. I did this because 1L weighs 1kg I then used it in my...
  33. A

    How to Determine the Products of Chemical Reactions

    I'm in an intro chem class right now and I honestly have no clue where I was when they talked about this BUT here goes... I have several spot tests that I have to come up with the formulas for, I have the reactants just have no clue what the products are. I understand how to balance formulas I...
  34. J

    Change in coffee taste under certain conditions - chemical explanation?

    I'm just wondering if someone can point me in the right direction here.. or maybe I'm just crazy lol. I'm a big coffee drinker. When I go out, I usually grab a coffee and walk around with it in hand. (mall's, convenience stores, book stores, subways and buses etc...) and as expected there is...
  35. J

    Toxic chemical compounds used in products that you are aware of

    What are some dangerous chemical compounds and substances that manufactures put into products that you are aware of and recommend avoiding ? (Is there anything not mentioned here? What are some other toxic compounds?) -Plastic items such as shoes, plastic trash bags contain PolyVynyl Chloride...
  36. K

    Steady-state/ dynamic models of chemical reactors

    Hi everyone, I'm trying to solve a problem concerning steady state and dynamic models of chemical reactor. I attached the problem statement for better understanding. Please disregard part (a). Here's what I have come up with so far: For part (b) I have the following From Mass Conservation...
  37. S

    Chemical Bonding: Does CN Neutral Exist?

    Does CN neutral exist? if it will their will be a triple bond but their will be 1 single electron left in the carbon atom now if answer is yes i am all good but if no then why can't 1 unpaired electron remain unbonded?why has it always got to be a "pair" of electrons?
  38. G

    Writing chemical equations for TLC analysis?

    I just submitted a lab report for a TLC experiment, but I just realized that I completely forgot to include the "reactions" section. It's too late to save that grade, but for future reference, how would one go about writing out a chemical equation for a TLC experiment? I had always understood...
  39. R

    Calculation of enthelpy and internal energy or air in chemical equilibrium

    Homework Statement Consider air in chemical equilibrium at 0.1 atm and T=4500 K. The chemical species are O2, O, N2, N (Ignore NO). Calculate the enthalpy and internal energy per unit mass of the mixture. Neglect electronic excitation in your calculations. K_{p,O_2}=12.19 atm...
  40. M

    Barium Chromate chemical equilibria

    1. Recently did a lab experiment involving Barium Chromate. 1) When BaCl2 and K2CrO4 were mixed, I obtained a colourless solution and a yellow ppt was formed. This solution and ppt were split into 3 test tubes. 2) When HCl was added to tube 1, i got an observation that an orangey yellow...
  41. L

    Comparing Cl 35 and Cl 37 Chemical Reactions

    what difference,if any are expected between the chemical reactions of Cl 35 and Cl 37? I'm not sure how to attempt this question =/
  42. A

    Help Needed: Dealing with a Failed Chemical Reaction Engineering Course

    First of all, I'm asking here for advice since I've seen how the members of this forum answer in a mature manner (I've read some problems like mine in the forum, however, I've not contributed some). your advice is very much appreciated (please don't mind the different field of study) I've...
  43. X

    What's the relation between chemical compositions and physical properties?

    Dear all, is the relation between chemical composition of a material and its physical properties a peering relation or a relation of subordination？
  44. R

    Environmental / Chemical Engineering Problem Help

    I have a environmental engineering problem to do for homework, it goes like this: How many mg/L of magnesium ion will remain in solution in water that is 0.001000 M in hydroxyl ion and at 25 degrees celsius? the answer is 0.1367 mg/L, but i don't know how it was found. to be honest I...
  45. S

    Understanding Chemical Bonding: Why Last Sublevel Electrons Matter

    hello, to preview chemical bonds must be considered only the electrons in the last sublevel and not the electrons in all the level? for example my book talking of carbon sp hybridation say that we shouldn't expect it make 4 bounds but only 3, why if the carbon need exactly 4 electron to...
  46. D

    Find Chemical Potential of Ideal Gas: Gibbs-Duhen Relation

    Homework Statement Find the chemical potential for an ideal gas as a function of temperature and pressure. Use the "Gibbs-Duhen relation". Homework Equations \mu=\frac{\partial U}{\partial N} dU=TdS-pdV+\sum\limits_{i}\mu_{i}dN_{i} U=Q+W Gibbs-Duhen relation...
  47. T

    So how do you know when a chemical is an acid or not? I know that an

    So how do you know when a chemical is an acid or not? I know that an acid is a compound that, when dissolved, yields H atoms, but does that mean than any compound with H in it is (or has the potential to be) an acid? For example: HNO2, I put down that it was Hydrogen Nitrite, but the...
  48. M

    Detonation-Physical or Chemical

    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 ...
  49. 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...
  50. 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
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