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

    Can a Chemical Reaction Solver Determine Reaction Products?

    Is there any type of software that can figure out the product of a reaction, such as organic chemistry reactions?
  2. J

    Difference in chemical potential(mu) problem

    Homework Statement Given: 2 cups of hot coffee, each 250 mL, T=50 degrees celsius, 323.15K 1 cup is sweetened 1tsp (5cm^3) of sucrose (342.3 g/mol) the other cup is sweetened with 1g saccharin (183.17 g/mol) assume coffee is very weak so the sweetener is the only solute density of H2O at...
  3. T

    Chemical Engineering Specializations

    I am planning on doing a Masters degree, and my current options are: Process Systems Engineering, Advanced Chemical Engineering, Materials Science, Nanotech, Biotech/Bioprocess Engineering, Catalysis, Chemistry or Nuclear Engineering (Very unlikely). So I am wondering... If I am not yet sure...
  4. C

    Balancing a complex Chemical equation

    Homework Statement Balance the following Chemistry equation, you are allowed to add H{+} and H2O where needed Given C6H5OCl + NO3- --> N2 + Cl- + CO2 2. The attempt at a solution Balance the carbon first: C6H5OCl + NO3- --> N2 + Cl- + 6CO2 Increase Oxygen O in NO3{-} to compensate...
  5. C

    From chemical engineering to aerospace engineering

    I am about to finish my Chemical engineering degree, but i am starting to lose interest in it. instead, I am getting really interested in aerodynamics, jet propulsion, aircraft design, and other stuff involving aerospace/aeronautical engineering. I was wondering if it is possible to get an...
  6. B

    Mass loss in common chemical reactions?

    In any common chemical reaction that releases energy, say the reaction 2H2 + O2 = 2H2O, what mass is converted to energy via the E = MC2 equation? What sub-atomic particles are converted to energy during ordinary chemical reactions? I was taught us in HS and under-grad chemistry classes that...
  7. E

    Chemical and phase equilibria, A12 and A21 for Infinitely dilute.

    Homework Statement (a) The activity coefficients at infinite dilution for isopropanol and water are 11.825 and 2.986 respectively at 80°C and 1 atm. i) Calculate the van Laar Coefficients A12 and A21 [b]2. Relevant equation. A12=lnγ (1+((x2lnγ2)/( x1lnγ1))^2) The eqaution for A21 is the same...
  8. D

    Are Matrices, Quantum Physics helpful in Chemical Engineering?

    I am a sophomore majoring in Chemical Engineering. I have checked my classes requirement and seen that Chem E major doesn't need Matrices math or Quantum physics. I am wondering how so? And also, I am currently have 2 credits free for Spring semester. I am wondering should I study...
  9. J

    Physics vs. Chemical engineering, difficulty

    I've heard that engineering (generally) is less difficult than physics but I've also heard that ChemE is the most difficult engineering degree to get. So which is more difficult to get: a B.S. in Physics of a B.S. in ChemE? If ChemE is eaiser, exactly how much easier is it: considerably or only...
  10. V

    Help with balancing a chemical equation algebraically

    Homework Statement (a)H2SO4 + (b)NaHCO3 -> (x)Na2SO4 + (y)CO2 + (z)H2O I gave each element it`s own equation: (1) For hydrogen – 2a + b = 2z (2) For sulphur – a = x (3) For oxygen – 4a + 3b = 4x + 2y + z (4) For sodium – b = 2x I then assigned a number to letter 'a'. My book says...
  11. Einj

    Question about chemical potential

    It is probably a silly question, but here it is. Suppose we have a gas composed by two different kinds of particles. There will be two different kinds of chemical potential? One for each specie?
  12. G

    Engineering M.S. in Chemical Engineering Interested in Informatics

    Dear all, I recently completed a M.S. in Chemical Engineering and I am finding that I lost my drive. I am instead more passionate about Informatics. I opted for trying to learn things on my own because I did not want to take on debt to pay for college. It worked out considerably well. I learned...
  13. Telemachus

    Chemical equilibrium, getting molarity given pH and Kb

    What should be the molarity in an aquatic dissolution for Trimethylamine, ##(CH_3)_3N## if ##pH=11,2##? ##(CH_3)_3N+H_2O \rightleftharpoons (CH_3)_3NH^++OH^-##, ##K_b=6.3 \times 10^{-5}## I know that ##pH+pOH=14 \rightarrow pOH=2.8##, then ##[OH^-]=1.58 \times 10^{-3}## And...
  14. H

    Determining the atomic number, mass number, and chemical name during beta decay

    Determining the atomic number, mass number, and chemical name during beta decay! Homework Statement The image below shows the element Thorium with the atomic number listed above and a mass number of 233. This element undergoes two successive beta decays. The resulting nucleus will have an...
  15. K

    Chemical Equilibrium with Multiple Kc

    Homework Statement Compound A can react to form B and C according to the following A<->2B Kc=1 A<->C Kc=1 If 1 mole of A is solved into 1 litre of water, what will the concentration of A be after equilibrium has been reached?Homework Equations ICE-tables(?) A<->2B+C Kc=([B]^2[C])/[A] The...
  16. S

    Chemical Reactions of Substances & Professors' Advice

    [1] Good afternoon anyone! I am a Petroleum Engineering student at Palawan State University and conducting a research. I have seen a topic of research, and it is: The Production of Petrol from Air and Electricity, and I need to find some reaction equations for my topic, here are some: Air...
  17. S

    [Doubt] Chemical Potential of an Ideal Gas

    Homework Statement Basically, find the chemical potential of an ideal gas knowing its heat capacities.Homework Equations P V = n R T \ \ \ \ (1) U = n c_V T + U_0 \ \ \ \ (2) S = S_0 + n c_V ln (T) + nR ln (V) = S_0 + n c_V ln (T) + nR ln \left ( \frac{nRT}{P} \right ) \ \ \ \ (3) \mu = \left...
  18. B

    [Chemistry] Chemical Reaction, limiting reactants and result stoichiometry

    Homework Statement 609.5 grams of vanadium (II) oxide, VO, and 832 grams of iron(III) oxide, Fe2O3, react according to the equation, which substance(s) and how many grams of each would be in the tube after the reaction completes? 3 points Homework Equations Equation: 2 VO + 3 Fe2O3 -> 6 FeO...
  19. J

    Is there free software for drawing chemical stick models?

    Is there any free software for drawing nice neat chemical stick models? I'm just looking for simple software to make the simple stick drawings of the chemical structures. I have software for drawing "ball and stick" type drawings, i use Avogadro chemistry software. Its software for drawing...
  20. W

    Halved volume with chemical equilibrium

    Homework Statement The reaction is PCl5 (g) <=> PCl3 (g) + Cl2 In an unknow volume, the following mixture is balanced: 0.14 atm of PCl5 0.36 atm of PCl3 0.50 atm of Cl2 What would be the the pressure of the whole mixture if the volume would be halved? (the answer is 1.88 atm) Homework...
  21. C

    Programs How Competitive Are Chemical Physics PhD Programs?

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  22. P

    Chemical energy into mechanical.

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  23. O

    Chemistry Calculate Reactant Concentration from Chemical Equilibrium Moles

    If someone could check my work on this, I'd appreciate it: Thanks!
  24. Y

    Looking for chemical that can clean hard water stain on glass.

    I have a very hard time cleaning out the hard water stain and soap scum on the shower door glass. I tried the normal cleaning spray. I tried using Vinegar( acetic acid), Lime juice (citric acid) with no luck at all. Any suggestion on what I can try?
  25. Y

    Chemical Potential for Bosonic Particles

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  26. G

    Can Heat Weaken Chemical Bonds and Make Them Easier to Break?

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  27. O

    Chemical Kinetics - Concentration/time

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  28. B

    Schools What do chemical engineers build in college?

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  29. T

    Engineering Chemical Engineering Personal Statement Help

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  30. J

    Energy required for a chemical reaction

    Hi all, I'm looking for the energy required for a 2-step chemical reaction: CaSO4 + S2 -> CaS + 2SO2 CaS + 3CaSO4 -> 4CaO + 4SO2 This reaction is to happen around 1600 deg. F. I solved for the heat of reaction for these two reactions with the following enthalpy equation: H2=H1+∫CpdT I...
  31. C

    Markov property and chemical oscillators

    Hi everybody... I've been working a bit with models of chemical oscillators and I've run into something that isn't quite clear to me. Chemical reaction systems are typically regarded as having the Markov property -- they lack memory and their evolution depends only on their current state...
  32. U

    How Does the Mean Life of a Radioactive Element Affect Its Activity Over Time?

    Homework Statement The mean life of a certain radioactive element is 6 hrs. By what fraction will its initial activity decrease over a time period of 5 hrs. Homework Equations t_{avg}=\frac{1}{k} Initial Activity = kN_{0} Final Activity = kN_{t} The Attempt at a Solution From eqn 1...
  33. N

    Can chemical engineers work in aerospace?

    So I've well into my first year at university, but I have been having doubts about my degree already.. It seems like I never thought about what I REALLY wanted to do during high school. So due to me enjoying a mix of physics, chemistry and math, I chose ChemE.. However, I've always been...
  34. L

    If pH is below pKa, chemical will be protonated: corresponding rule for pKb?

    The rule that if the pH of solution is below the pKa of a molecule then that molecule will be protonated is a handy rule. However, I'm finding it difficult to find the pKa of the chemicals I'm working with. This mostly applies to looking at nitrogens in organic compounds. For example, it is...
  35. A

    Computer Software Engineering vs Chemical Engineering

    Basically. I'm a sophomore at Stony Brook University and I was doing biomed but now I think I want to be a software engineer so, I'm trying to get into the Computer Engineering program at my school. I did research and I learned that software developers/software engineers are growing in demand...
  36. N

    What is the best way to find a specific chemical for a lab class?

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  37. S

    Engineering Questions About Chemical & Electrical Engineering for Undergrads

    Hello, Can some one please help me out I am going to be starting my undergrad and i wanted to know about chemical and electrical engineering. I wanted to know the following things. 1) which of these two is more in demand? 2) which of these two is easier? 3) in which engineering will i get a...
  38. N

    Chemical Kinetics QuestionDetermination of order of reaction

    Homework Statement So the question says for the reaction 2N2O5(g) --> 4NO2 (g) + O2(g) provides a linear plot when P(N205) is plotted against t with a negative slope . The decomposition of N2O5 follows ? Homework Equations The Attempt at a Solution I am guessing that P(N205) is...
  39. S

    Solutions and colligative properties and chemical kinetics combined ques.

    a mixture of two miscible liquids a nd b has 10 moles of a and 12 moles of b. pure vapour pressure of a is 300mm Hg and tht of b is 500mm of hg. as soon as b is added to solution A starts polymerising into an insoluble solid. after 100 minutes 0.525 moles of a solute C is added whch stops...
  40. S

    Solutions and colligative properties and chemical kinetisa combined ques.

    a mixture of two miscible liquids a nd b has 10 moles of a and 12 moles of b. pure vapour pressure of a is 300mm Hg and tht of b is 500mm of hg. as soon as b is added to solution A starts polymerising into an insoluble solid. after 100 minutes 0.525 moles of a solute C is added whch stops...
  41. C

    Chemical to absorb oxygen and nitrogen

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  42. V

    Overlap between physical chemistry and chemical engineering?H

    How much overlap is there between physical chemistry and chemical engineering with regards to thermodynamics, kinetics, and transport phenomena? Would it be beneficial for a chemical engineering student to take the physical chemistry courses that deal with these topics? Or would it be redundant...
  43. N

    Chemical Kinetics Qn: Why is D Not a Possible Answer?

    The correct answer states its C which i understand why since doubling the intiial volume of SO2 is equivilent to doubling the intial moles of SO2 hence the moles of SO3 produced will also increase and hence pressure exerted shld be higher than before which is not reflected by the graph...
  44. A

    Chemical Kinetics - Activation Energy and gr

    The problems are Number 12 and 13 on this link http://isites.harvard.edu/fs/docs/icb.topic1096438.files/PS4.pdf I have the value of k for sum number 12, it is 1.54*10^-4. Im completely stuck with number 13 cos I'm unfamiliar with that concept and it kinda went over my head in lecture...
  45. J

    Should I Switch from Chemical Physics to Geophysics?

    I have been accepted into a chemical physics PhD program with a concentration in optoelectronics, but now I'm considering geophysics as a more preferable major. However, I've already said I would attend and there doesn't seem to be enough time to apply to a different school. Furthermore...
  46. M

    Chemical Batteries (Car Batteries)

    Why does the effectiveness of a car battery seem to drop off rather sharply when the voltage gets a bit below 12? I would think it would be more or less a linear decay of current ( I = V/R etc). Thus one would think that the current generated would be proportional to the voltage but anyone...
  47. M

    Is a Collision Between Three Molecules Necessary for the Formation of 2SO3?

    For the reaction, 2SO2(g) +O2 (g) ->2SO3. Why is it wrong to say that the reaction must involve a collision between one O2 and two SO2 molecules? Don't they form S2O6, which is equivalent to the product, 2SO3? What should I say then, about the reactants in forming 2SO3? Thank you so much!
  48. M

    The collision theory of chemical kinetics

    I am studying the activation energy of a reaction, and I notice that it says when the products are more stable than the reactants the reaction is exothermic, and endothermic when the products are less stable than the reactants. It doesn't say why, but my supposition is that when the products...
  49. J

    Chemical engineering with a phyisics dgree?

    Chemical engineering with a physics degree? I'm currently in college and have decided to major in physics with a minor in chemistry. Can this type of bachelor's degree get me a job as a chemical engineer? Before anyone asks, I don't want to get a degree in chemical engineering because I might...
  50. Y

    What is the chemical formula for car exhaust emission

    What is the chemical formula for car exhaust emission
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