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. O

    Writing chemical equations w/ catalysts

    hi. for a science lab in school we were discussing/exploring chemical equations... we had hydrogen peroxide (H2O2) which was catalyzed by potassium iodide (KI) for our lab report we need links to a website which describes how to properly write equations w/ catalysts. so firstly is this right...
  2. R

    Calculating Mole Fraction and Kp in Chemical Equilibrium

    Chemical equilibrium help! For a reaction 2SO2(g) + O2(g) ↔ 2 SO3(g), 0.1mol of each SO2 and SO3 are mixed in a 2.0L flask at 27 degrees Celsius. After Equilibrium total pressure is 2.78atm. Calculate a) The mole fraction of O2 at equilibrium b) The value of Kp I don't know how to find out...
  3. F

    Light emission/absorption revisited by chemical thermodynamics

    Hello, using the words of chemical thermodynamics could we say that stimulated emission of light is "catalysed" by incident photons, as well as absorption ? In that way, does it mean that there is a kind of "activation energy" in the emission process ? Without incident photon...
  4. M

    Can Non-Metallic Triggers Be Used in Sodium Acetate Heat Packs?

    Does anybody have any idea of whether or not a non-metallic trigger could be used in sodium acetate heat packs. The crystalisation preocess in the packs is triggered by bending the metal disks inside them which causes heterogeneous nucleation. Are there any plastics which could work where...
  5. D

    Chemical Engineering Program Accreditation and Curriculum: Is it Worth the Wait?

    Hey. I've just finished my first year of uni, and it is almost time to enrol in next years units. I have been kicking up between chemical and mechanical engineering for the past year, but after much research, i think ill go with chemical and process engineering. I was reading about the...
  6. H

    Looking into chemical engineering

    Interesting website you got here, found it by accident... looks like lots of smart peoples around here, maybe I can get smarter if I stick around. Little about me, just a young dude looking into chemical engineering, renewable energy and stuff like that, seems like the "in" thing nowadays, maybe...
  7. Wellesley

    Schools Best Chemical Engineering Undergraduate Schools

    I'm curious about what people consider is the best ChemE school. What schools do employers like to see applicants come from? This list excludes MIT, Cal Tech and other premier schools that are already rather obvious. Thanks for all suggestions.
  8. B

    Fuel may be designated by the chemical formula C51 H105 S2 (OH)3

    Homework Statement A fuel may be deignated by the chemical formula C51 H105 S2 (OH)3 Write out the balance equation for complete combustion of this fuel. Homework Equations Cx Hy Oz Sn [(x) + (y/4)] o2 > xCo2 + (y/2) H2o The Attempt at a Solution The problem is that I...
  9. J

    How Do You Balance the Equation for Copper (II) Chloride Dihydrate and Aluminum?

    Homework Statement Copper (II) Chloride dihydrate is mixed with solid aluminum. Find the products and balance the equation. Homework Equations N/A The Attempt at a Solution The original equation that I got was: CuCl2 ∙ 2H2O + Al --> AlCl3 + Cu + H2O When I balanced it, I got: 3...
  10. M

    Solving Chemical Kinetics Homework for A, B, C & D

    Homework Statement Write down the material balance for the components A, B, C, D id this reaction takes place in a batch reactor: A+B\UpdownarrowC and C+B\UpdownarrowD The difunctional starting material (A) combines with the primary reactant (B) to form a monofunctional intermediate (C)...
  11. H

    Where Can I Find Affordable and High-Quality Chemical Vendors in the US?

    I am in charge of purchasing chemicals for my department in the university and I was wondering if anybody knows any good chemical vendors in the US. I know the basic ones like Sigma, Fisher, Acros, Brandnu, Spectrum, JTBaker, and GFS, but I was wondering if there are other places that have...
  12. D

    What is the chemical name for OI2?

    Homework Statement What is the chemical name for OI2? Does Nickel have more than one charge like most other transition metals? I think the name for OI2 is Oxygen diiodide. This sounds really weird. How about other instances if there are I3,I4,I5 or even I6 in a covalent compound? One of my...
  13. D

    Mass Relationships In Chemical Reactions

    Homework Statement Styrene is a Hydrocarbon. If 0.438g of Styrene is burned in Oxygen and produces 1.481g of CO2 and 0.303g of H20, what is the empirical formula of styrene? Homework Equations The Attempt at a Solution No. of moles of CO2 - 1.481g / 44.0107g/mol = 0.0337mol No...
  14. F

    How do I calculate the length of a chemical bond?

    “In C6H8, the carbon atoms are connected in a chain. In a rough approximation, some electrons can be viewed as confined to a line with the length of this chain. C6H8 absorbs ultraviolet light with wavelength 357 nm, which causes an electron to change from the third lowest allowed energy to the...
  15. E

    Shielding Effect and Chemical Shift

    Homework Statement Given a molecule of chloroethene (vinyl chloride) or ClCH=CH2. Rank the hydrogen atoms in the molecule in terms of which will have the greatest chemical shift. Homework Equations None The Attempt at a Solution Since the Cl and the double bond are both...
  16. J

    Does p-Toluidine Hydrochloride Dissolve in HCl?

    chemical reactions with hydrochloric acid does p-toluidine hydrochloride dissolve in HCl?? When it combines with HCl, what would it produce?
  17. J

    Does p-toluidine hydrochloride dissolve in water, HCl, NaOH, or NaHCO3?

    Does p-toluidine hydrochloride dissolve in water, HCl, NaOH, or NaHCO3? How would you write the chemical equations of the reactions?? if a salt is formed... how do you write that in an equation showing the structural formulas?? If it dissolves in water, if you add drops of HCl or NaOH to the...
  18. G

    Chemical Equilibrium: AgCl + NaCl Effects

    a question on equillibria "Ionic compounds we normally designate as insoluble in water e.g. AgCl actually dissocitae to a small extent into constituent ions. these aqueous ions are in equillibrium with the solid as indicated in the following equation AgCl(s) \Updownarrow...
  19. S

    An egg is fried in a skillet, a chemical or physical properties?

    Please help urgent Please help, I have few questions 1.Natural gas burns with a yellow flame, a chemical or physical properties? 2.An egg is fried in a skillet, a chemical or physical properties? 3. When iron is dissovled into a acid. Has the iron atoms destroyed? Give answers with...
  20. N

    Use of computers in chemical engineering

    I have a passion for computers/ electronics, but i am going for either chemical or petroleum engineering. I want to ask how much do chemical and petroleum engineers use computers and other electronic devices for their work ? I don't want to do something which involves most of mechanical...
  21. C

    Two repulsive/attractive forces that influence chemical bonds between two atoms

    I need to identify two repulsive forces and two attractive forces that influence the formation of chemical bonds between two atoms. this is what i understand so far: 1.chemical bonds between two atoms--> this is intermolecular forces 2.type of intermolecular forces--> Dipole dipole, van...
  22. T

    I understanding how to read and write chemical formulas

    I am in a Chem 105 course. I don't have a homework assignment but we do have a test coming up and I have some worksheets to help me practice writing formulas. My question is how do you know if the formula has a charge. For example: Sodium Nitrate - I know Sodium is Na and I know Nitrate is a...
  23. A

    Chemistry Basics: Learn Chemical Nomenclature

    Any good sites for it? I'm just starting chemistry, so none of that complex crap. Just the basics will be good. Thank you.
  24. R

    What is the Chemical equation of this?

    Complete and balance the ff. chemical equations. Identify the equation as to the type of chemical change. 1.Magnesium + Hydrochloric acid ---> Zinc chloride + Hydrogen gas 2. Zinc + Hydrochloric acid ---> Zinc chloride + Hydrogen gas 3. Iron + Sulfuric Acid = Iron (II) Sulfate + hydrogen...
  25. V

    Arrhenius Equation - Chemical Kinetics

    Hello everyone, I am having trouble with determining where I erred in the following exercise. If someone could point out my mistake, I would appreciate the help. Thank you! --- 1. The decomposition of N2O5 has an activation energy of 103 kJ/mol and a frequency factor of 4.3E13 s^-1 . What...
  26. P

    Does Chemical Reactions Affect Mass?

    Does mass of compounds change due to exothermic/endothermic chemical reactions?
  27. A

    Needed: All information on chemical Eng.

    Hi all. Been browsing the forums for a while and really like what I have read so far. In my reading I have been on the hunt for any topics or threads involving chem. eng. but have been sadly dissapointed. I really am interested in this area but could not find many threads involving it except...
  28. M

    Courses Math courses for Chemical Physics?

    Other than four semesters of calc., are there any other math courses to take as an undergrad to be well prepared for a PhD program in Chemical Physics? If so, what? Thanks.
  29. D

    How Does Hydrogen Sulfide Affect pH and Precipitation in a Cu-Zn Solution?

    Homework Statement A sol'n contains Cu+2(aq) and Zn+2 ions each at a con'c of 0.1M. Hydrogen sulphide gas is bubbled up into sol'n and dissociates having an initial con'c of 0.1M. Whats the pH of the final solution? Will any precipate form? I don't know how to start the problem. Pls help me...
  30. W

    Mass Conservation in Chemical Reactions

    I realize that to calculate heat being released and contained during nuclear reaction you must understand the difference between its product mass and reactant mass by using *E=mc2.* My Question pertains to the heat being released during a chemical reaction... Is Mass conserved in this chemical...
  31. B

    Estimating the expected yield of a chemical reaction

    Scenario: Suppose that a pump creates a partial vacuum, which is used to input air (gas) from the environment into a long tube. At a certain point within this tube, diatomic hydrogen and oxygen (gases) are also inputted into the tube. The tube outputs back into the environment. I have...
  32. Q

    Low Temperature Expansion of Chemical Potential

    I'm trying to derive a low temperature series expansion for the chemical potential of a weakly interacting Fermi gas. The starting point is, of course, the Fermi-Dirac distribution function (p is the particle momentum): f(p) = \frac{1}{e^{\beta(\epsilon(p) - \mu)}+1} , where, in the...
  33. U

    Exploring REUs for Chemical Engineering Majors: What to Know

    Sorry if this sounds stupid, but I will be a freshman next year and I have no clue what it is. I understand that it's research experience for undergraduates, but how exactly do you enter one of these programs, and what exactly do you do in them? Btw, I will be majoring in Chemical...
  34. G01

    Chemical Etching of Iron and Gold

    Hello All, I have a sample which has been covered in a layer of iron and gold for protection. So, in order to work with the sample, we need to etch away the metallic layers. I hear there is a specific chemical recipe for chemically etching away iron and gold from a sample. If anyone can link...
  35. O

    Navier Stokes with chemical reaction

    I wasn't sure whether to put this in Aerospace, but decided on physics in the end. 1.) How do you factor a chemical reaction into the solution for the Navier Stokes equations? More precisely, how can you include the affects of a heat absorbing (endothermic), or heat releasing (exothermic)...
  36. MathematicalPhysicist

    Chemical Potential and Atmospheric Molecule Distribution at Constant Temperature

    The question is from kittel's book, thermal physics: If n concentaration of moleclues at the surface of earth, M the mass of a molecule and g and gravitational acceleration at the surface, show that at constant temprature the total number of molecules in the atmosphere is N=4\pi...
  37. S

    Chemical Engineering Thermodynamics

    One mole of supercooled liquid tin (Sn) is adiabatically contained at 495K. Given: the melting temperature of Sn, Tm, Sn = 505 [K] the enthalpy of fusion of Sn, hfus, Sn = 7070 [J/mol] the heat capacity of liquid Sn, Cp, Sn(l) = 34.7 – 9.2 x10-3 T [J / (mol K)] the heat capacity of solid...
  38. U

    What is the meaning of chemical energy, in terms of first principles?

    We're all familiar with exothermous reactions, where chemical energy is converted to heat. However, I have not seen a satisfactory explanation of this from first principles, ie electromagnetic forces between charged electrons and nuclei. How does the force between charges and the associated...
  39. M

    Trivial question about chemical rxns

    I don't really get how chemical rxns are formed...sad but Le true If you have the compound Na_{}2CO3 dissolved in water how do u know what's formed? B)How do u know soluble it is/if it is an acid or base?
  40. R

    Uncovering Citric Acid's Chemical Composition and pH

    [SOLVED] pH question... i'm writing a research paper on the organic medicinal massage oils. i need to know the chemical composition of citric acid and it's pH. can anyone help me?
  41. S

    Courses Intro course on different types of chemical families

    Hello Physics forums! Im currently in Grade 10 learning the intro course on Chemistry. Can someone lead me to the right direction if I want to advance study for Grade 11 Chem? Please and thank you! :biggrin: EDIT: BTW Grade 10 Chem was just an intro course on different types of chemical...
  42. H

    What is the value of Kc for this equilibrium reaction?

    Homework Statement A 1.0 dm3 reaction vessel contains initially 1.0 mol of N2O4(g) and 1.0 mol of NO2(g). At equilibrium, 0.75mol of N2O4(g) are present. What is the value of Kc? A. 0.33 B. 0.50 C. 2.0 D. 3.0 The Attempt at a Solution Right answer = D, but I do not why. My attempt...
  43. M

    How can we use lemon and vinegar to create a specialized hot tub cleaner?

    My chem ISU involves taking a product in existence already and redesigning it (chemically) to become more environmentally friendly. These terms are very loose, and so, in my brainstorming, I've been thinking of using lemon juice or lemon OIL even (not sure how to extract the oil though) and...
  44. B

    Chemical form of uranium in a bomb?

    I understand that uranium is typically fabricated into uranium dioxide pellets when used in nuclear fuel rods; however, I can't seem to find what form it is put into when used in a nuclear bomb. I am guessing either UO_2 or uranium metal?
  45. M

    Solving the Kc of a Chemical Reaction with N2O4

    heey i have this chem homework quest : 5 L flask is filled with 0.625 mol of (N2O4) if you know that concentration of (N2O4) at equilibrium = 0.075 M what is the kc for the rxn ?? 2 NO2 → N2O4 ←
  46. C

    Chemical Equilibrium: Co(H2O)62+ + 4 Cl- ----> CoCl42- & 6 H2O

    I am totally confused with this question and have trying to figure it out for hours! Co(H2O)62+ (aq) + 4 Cl- (aq) ----> CoCl42- (aq) + 6 H2O (l) The equilibrium constant K = 4.82x 10-4 We begin by putting enough [Co(H2O)6]Cl2 (assume the salt dissociate completely into ions) into 100.0...
  47. R

    How to determine the product of a Chemical Reaction.

    Ok the question is some what simple and difficult. I know there are certain rules like a. A + B = AB (combination) b. AB = A + B (decomposition) c. AB + C = CB + A (substitution) d. AB + CD = AD + CB (metathesis) now the trouble i have is not in balancing the equation but figuring out...
  48. S

    Chemical info needed to break ceramic tile

    Hi , please can anyone help. I need to know what chemical i could use that when drawn on a glazed ceramic tile it will break in the exact place. thanks stuart
  49. L

    Calculating Salicylic Acid Required for Aspirin Production

    Aspirin, C9 H8 O4 (molar mass 180.2g/mol), a drug used to relieve minor aches and pains, is prepared by the following reaction: C7 H6 O3 (s) + C4 H6 O3 (l) --> C9 H8 O4 (s) + C2 H4 O2 (l) If you need to prepare 45.0g of aspirin, and yield for the reaction is 85% how many grams of salicylic...
  50. K

    Chemical Equation: Dissociating PbBr2 - Ksp of 6.3E-6

    the Ksp of lead (II) bromide is 6.3E-6. A large amount of PbBr2 sits at the bottom of a beaker with water above it. Equilibrium is reached. Write the chemical equation fo rthe dissociation of lead II bromide as it dissolves for which the Ksp applies. -How would i go about solving this problem?
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