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. J

    Chemical Engineering B.S to Nuke Eng M.S?

    Hello, I am studying Chemical Engineering at the University of Oklahoma. I have recently become very interested in Nuclear Engineering, but unfortunately my school does not offer the degree. Is it possible to go from a Chem E b.s to a Nuclear Masters? Thanks!
  2. E

    Engineering Advice? double majoring in chemical engineering and physics

    I'm starting college as a freshman in september, double majoring in chemical engineering and physics. It is one of the best engineering schools in the US, and I was accepted into the honors program. Physics is sort of a hobby for me. I just added it as a major because it wouldn't be difficult...
  3. C

    Can chemical reactions take place at absolute zero?

    Title says it all. I've been wondering. The argument is, is there a minimal temperature required for any chemical reaction to reach its activation threshold? Or would the energylessness of the atoms prevent bonds from forming (or dissolving, I guess)? Conrad.
  4. N

    3D Printer Resin's Chemical Makeup?

    Does anyone know what compounds make up the resin used by resin type 3D printers? I need to know if it could possible react with some hexane, toluene, and other chemical solutions for sure, though I believe the resin to be fairly inert chemically. Thanks PF.
  5. M

    Is Chemical engineering the same as Chemical Technology

    The title is self explanatory. Thank you
  6. P

    What chemical solution to use for cleaning digital camera sensors?

    Since it is impossible to get certain cleaning solutions (in Canada, at least) like "Eclipse" (methanol) and pure isopropyl alcohol (from drug stores) is adulterated with some kind of greasy oils that leave smear marks behind, I would appreciate some help as to what chemical solutions might be...
  7. J

    Which chemical reactions are possible?

    The question in the attachment is from an old entrance exam for medical school. The correct answer is B. I realize that if I assign a 'point value' to the levels of reactivity for each of the letters i.e. the more reactive the higher the number T = 1 Q = 2 M = 3 J = 4 and that if...
  8. D

    Job dangers associated with chemical engineering

    Hello Pals, My fiance is going to school for chemical engineering. I have read the statistics pertaining to on-the-job fatalities and general risks associated with this career. I warn him daily that he will face substantial risk to his health resulting in, but not limited to; face splash...
  9. S

    Enthelpy change for chemical reaction

    hi I'm taking GCE O levels so this might give you an idea of my level of chemistry. For a reaction like 2H2O2-->2H2O+O2 and the question tells me it has an ΔH=-98kJ/mol so does it mean that when 2 moles of hydrogen peroxide decomposes to form water and oxygen, the net amount of heat generated is...
  10. L

    Is recognizing beauty a chemical process?

    Why do we recognize a stream of sunlight going through the clouds causing a river to glitter as beautiful. Is it a chemical process? Why would we recognize something like that outside of ourselves that has no use as beautiful? And how would that fit into the theory of evolution and biology if...
  11. O

    How to remove the chemical smell from plastic?

    My new plastic toy has a strong chemical smell, does anyone have any suggestions on how to remove this smell? Thanks in advance for any suggestions
  12. Q

    Is COD Measured in Mol/Litres or mg/L?

    Can we measure COD in Mol/Litres?
  13. V

    Engineering Do Chemical Engineers get to travel the world?

    Do Chemical Engineers get to travel the world? Hi, just wondering if chemical engineers get to travel the world for their job? Like if you think of civil engineers, their companies will regularly contract them to do projects overseas, similar to mech and elec engineers, but for chemical...
  14. H

    What does it mean for a chemical reaction to do work on a battery?

    Hi everyone! I basically understand how the materials used in the chemical reaction of a battery work but now I want to know why some batteries have different ratings of voltage. From what I've read, this depends on the materials that are used. What does it mean for some materials to do...
  15. J

    Determing The Chemical Formula of a Hydrate

    Homework Statement When copper (II) sulfate hydrate, a blue crystalline solid containing embedded water molecules (called a hydrate), is heated in air, it loses the water molecules and the blue solid is transformed to a white anyhydrous (no water) crystal known as copper (II) sulfate.Homework...
  16. jfizzix

    Chemical potential vs pressure and temperature; difficulty with Fermi gases

    For any system where the thermodynamic limit exists, we know that the internal energy U, the entropy σ, the total particle number N and the total volume V are all extensive. Because of this, we know that the Euler relation holds true U = -PV + \tauσ + \muN and that the chemical potential...
  17. V

    UC Davis or UC san diego for chemical engineering?

    I'm about to transfer out of a community college, and so far I got accepted to these two. I'm still waiting on Berkeley, but if I don't get in which of these two would be better if I want to go on to a phd program after undergrad? does it even matter? Thanks.
  18. N

    Exploring Entropy Production in Chemical Processes

    Hello, So presume we have a system in which a chemical process A + B -> X + Y is happening. We allow it to be a non-equilibrium process (so there will be an entropy production inside the system) but for ease we presume the system is characterized by the usual variables E, V, N_A, ..., N_Y...
  19. I

    Chemical Equilibrium: Understanding & Equation

    Can someone help me understand the concept of chemcial equilbrium. I think I understand in a certain chemical reaction, know matter the amount of reactants or products, the equilibrium constant will remain approximatly the same. I don't fully understand how the equation to solve for the...
  20. M

    Activity and chemical potential

    hi, can someone help me in understanding the difference between chemical potential and activity? Why it is important to know/determine activities of certain species in material growth? Given that activity is dimensionless quantity, what is it measuring? Also, what is the activity of pure...
  21. D

    Chemical diffusion derivation from thermodynamic factor and self-diffusion

    I am working through a paper in which the chemical diffusion coefficient is related to the self-diffusion (or tracer) through the following derivation, on which I am a little hung up. AB2 metal. Overall diffusion D= XADB+XBDA meaning the chemical diffusion of B is...
  22. N

    Engineering Chemical engineers working for space agencies?

    Hello. I am trying to choose between studying chemical engineering (MSc) or getting a master's degree as an engineer specializing in math&physics (yes, you can do that in my country). For this I have questions: 1)Are chemical engineers needed in Space agencies? Perhaps working on spacecraft...
  23. A

    Engineering Detailed Information on Chemical Engineering

    I'm only a Junior in High-School, but I know my passion resides in the field of Engineering. I love Trigonometry, Algebra, Chemistry. Whether or not i fail in some areas, and succeed in others, i always come out enjoying a process of learning in those areas. Chemical Engineering in a more...
  24. M

    Engineering Physics or Chemical Engineering?

    I plan to attend Rose-Hulman Institute of Technology, beginning next fall, but am having trouble deciding on a major. I was accepted as a Chemical Engineering major, but am now having some second thoughts. Throughout high school, physics has by far been the most interesting type of science to...
  25. M

    Engineering Chemical vs. Materials Engineering

    I've been doing some research on majors and have narrowed my interests down to something involving a mixture of chemistry and math, possibly physics as well. From what I have found Chemical Engineering and Materials Science and Engineering seem to be closest to my ideal mix, though the...
  26. S

    Chemical, material, or electrical engineering?

    hey guys I'm currently a first year engineering student and am at the point in my undergrad where I need to choose which engineering field i would like to go to. I've narrowed my choices to electrical engineering, material engineering, and chemical engineering. Could you please point of the...
  27. A

    How Do You Calculate Kc and Kp for a Reversible Gas Reaction?

    Homework Statement When 1.000 mol PCl5 is intorduced into a 5.000L container @500K, 78.50% of PCl5 dissociates to give equilibrium mixture PCl5, PCl3, Cl2 : PCl5--->PCl3+Cl2 (this eq. is reversible) (a) calculate Kc and Kp (b) if the initial concentrations are [PCl5]=.500M...
  28. S

    Will a Carbonate React with Carbonic Acid? A Chemical Reaction Explanation

    hi i was wondering if a carbonate will react with carbonic acid. such as calcium carbonate with carbonic acid: CaCO3+H2CO3CaCO3+CO2+H2O. Thanks for the help!
  29. A

    Aerospace or Chemical Eng. Career Help

    Hello, I am 25 years old and am returning to school a few years after I received a business degree and working in the upper-management industry. After much debate, I have decided to go back to school and get an engineering degree. I have quite a bit of background in STEM fields from my...
  30. H

    Chemical potential in thermodynamics to find latent heat of vaporization

    Doing some fun problems in Keith Stowe's 'An Introduction to Thermodynamics and Statistical Mechanics'. Good book. Problem statement: A certain material vaporizes from the liquid phase at 700 K. In both phases, the molecules have three degrees of freedom. If u_{0} in the liquid phase is...
  31. K

    How can we know/check the sun's current and latest chemical composition?

    Hello! We know that the sun started with about more than 70% Hydrogen and more than 20% Helium. with other metals consisting the remaining few percent. Now throughout its lifetime, this composition changes, especially with regards to the hydrogen in its core because of nuclear reactions...
  32. L

    Chemical kinetics diagramm -> chemical equation

    Hi everyone Homework Statement I got the three different diagramms (attached below) and I shall find a general chemical equation for all of them. Homework Equations - The Attempt at a Solution I think I know how to do the third one, but I have troubles with the first...
  33. H

    (at the most fundamental level) why does energy release upon chemical reactions?

    Please don't be bothered by my question, i know it sounds real elementary and it could easily be researched, but after doing so, i haven't been able to find anything on how or why the natural phenomenon of energy release takes place as chemicals react with one another. If you think about it...
  34. C

    Proper chemical to dissolve adhesive tape

    Hi everyone; I use usual adhesive tape (like scotch tapes) in one of my project and I want to get rid off the tape and all its remains at latter steps of my work. I want to do it with chemical methods so I used dichloromethane. But it only dissolve the plastic part of the tape but sticky part...
  35. R

    Chemical and electrical gradient for ion X+

    Please check my answers. I tend to over-think and get simple questions wrong. A hypothetical cell membrane is positively charged on the intracellular side and negatively charged on the extracellular side. In this cell, the concentration of ion X+ in the intracellular space is high and in the...
  36. Biosyn

    Medical Ion Proton 1: A Chemical Engineer's Dream

    What do you guys think of the Ion Proton 1 developed by a chemical engineer named Jonathan Rothberg? It can supposedly sequence most of a human genome for around $1000 compared to the past where had it costed millions. I don't recall quite clearly, but I think researchers at IBM are...
  37. R

    Alternative chemical energy storage

    Hi everybody. I have been thinking about this a while and could not come up with anything. I was wondering if there any chemical energy storage method that would have these properties: 1) it would be easy to produce 2) it would be easy to extract energy from 3) it would not have any carbon...
  38. JJBladester

    Thermo - Prove that a rapid chemical reaction is irreversible.

    Homework Statement Show that processes involving rapid chemical reactions are irreversible by considering the combustion of a natural gas (e.g. methane) and air mixture in a rigid container. Homework Equations Q_{in}+W_{e,in}-W_{b}=\Delta U+\Delta KE+ \Delta PE The Attempt at a Solution I...
  39. C

    Aspiring to get an M.S. in Chemical Engineering

    I have an A.S. in Chemistry and a B.S. in Mathematics and I am considering trying to earn a master's degree in chemical engineer. After working for an analytical lab for six months in sample receipt and prep I have spent a lot of time trying to find ways to improve my career. I understand that...
  40. A

    What's Left to Discover in Chemical and Thermal Physics?

    Are there any major questions yet to be solved in these fields? Also where exactly does thermodynamics, heat fit into physics?Thermal Physics?
  41. alemsalem

    Can internal energy levels of atoms affect chemical potential of ideal gas?

    μ/T represents the change in entropy if we change the number of particles,, so according to the fundamental assumption of statistical mechanics μ/T should tell us about the tendency of two systems to exchange particles... but I am having a hard time imagining how rotational or vibrational...
  42. L

    Switch to chemical engineering or stick with biochem?

    Hi everyone, my first post on here. I was hoping someone might have a few words of advice/suggestions. I'm a current sophomore currently pursuing biochemistry/molecular biology. My goal is to work in drug development of some sort, at a biotech company or so. Basically, I like to design and...
  43. R

    Find Remaining NO Concentration: 2NO + 2H2 → N2 + 2H2O, 0.006M NO, 0.002M H2

    2NO + 2H2 --> N2 + 2H2O The concentration of NO is 0.006 M and the concentration for H2 is 0.002M. How can I find the concentration of NO remaining when one-half of the original amount of H2 has been consumed? if you can also show me how it would be done if the reaction was not 1:1, that...
  44. V

    Heat-driven chemical reaction and thermodynamics

    If we use heat and a catalyst to crack water into oxygen and hydrogen, how can the efficiency of the process ever be less than 100%? Every joule that doesn't crack open the bonds and end up in the chemical energy of the products must end up as heat, and then we're back at square one. I'm...
  45. B

    Effect of Temperature on Chemical Equilibrium

    Hi guys I am a student of AP Chemistry. I am trying to understand the effect of temperature on equilibrium. I know that under the change of temperature, the equilibrium will shift to favor the endothermic process if heat is added and vice versa. But employing the Arrhenius Equation, I see a...
  46. K

    What are the chemical reaction happen indise lamp in tungsten

    Also the chemical involve in the W and iodine. Thx
  47. C

    Looking for a safe endothermic chemical reaction

    I’m not very well versed in chemistry so am asking for help. I’m looking for a couple of safe chemicals which combine to react (or dissolve etc.) endothermically. It doesn’t have to be an impressive reaction, it just has to be safe and not produce masses of gas (so that’s carbonate/ bicarbonate...
  48. O

    What is the chemical reaction with copper?

    Copper + NaCl + H20 = >> ? Does anyone have any suggestions on what chemical reaction will occur in above example? Thanks in advance for any suggestions
  49. L

    Searching for a Chemical Reaction to Produce Heat and Harmless Gas

    Hi, wondering if you could help me. I want to find a chemical reaction that would involve: Reactant + Air (or gases present within)----Exothermic----> Harmless gas Any help would be appreciated if you knew of a chemical that I could use to react with air to produce heat and a...
  50. MacLaddy

    Are My Chemical Reaction Equations Correct?

    Homework Statement I have a couple of problems here that are all part of one homework problem. A,B,C, and D. I have completed what I believe are the correct answers, but I really don't know for sure. This is an online chemistry class, and it really is not very good. I've watched about 3...
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