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Baryon (4/13)



  1. "Treatment of 3-methylcyclohexene with HCl yields 2 products, 1-chloro-3-methylcyclohexane and 1-chloro-1-methylcyclohexane. Draw a mechanism to explain the result." I can't really figure out one can arrive at 1-chloro-1-methylcyclohexane, how did the positive charge manage to shift to the CH3 position? Also, I read another textbook, and it features a question which states that "reaction of HBr with 3-methylcyclohexene yields a mixture of four products: cis- and trans-1-bromo-3-methylcyclohexane and cis- and trans-1-bromo-2-methylcyclohexane". Then shouldn't the HCl reaction yield products of similar structure? Thank you.
  2. Q: The central mechanical component in automobile engine is a piston-cylinder assembly, which allows the working fluid to function properly. Consider such an assembly with air as working fluid. The cross-sectional area of the piston is 0.1 m2. Initially the piston is at 1 bar and 25 C, 10 cm above the base of the cylinder. In this state, the spring exerts no force on the piston. The system is then reversibly heated to 100 C. As the spring is compressed (the spring is connected to the top of the piston), it exerts a force on the piston proportional to -kx, where k = 50000 N/m and x is the displacement from its uncompressed position. Air is assumed to behave as ideal gas. The atmospheric pressure is 1 bar. Determine the work done. (-166 J) I would like to ask, how is the heating "reversible"? The pressure of the system (gas) should increase, since the spring is being compressed, that means the force of the spring exerted on the piston is increasing and thus so should the counter force from the gas pressure. Here the temperature also increases, and so does the volume of the system. So it's not isobaric, isothermal, isochoric, right? I am stuck. i don't understand how it can be reversible, and what equations I can write out to start out solving the problem. Also the heat to the system, does it equate to work done by gas and heat lost? SInce the second law states that you can't convert all heat to work. Please explain thanks!
  3. I have difficulty understanding the Pxy diagram of a binary system (e.g. an ideal benzene-toulene mixture) and some facts in general, have been stuck there for hours, reading notes and everything but never seem to find or understand it. 1) Why is the bubble point line the line that indicates the total pressure of the system (partial pressure of benzene and toulene vapours)? 2) Why is the dew point curve and how do I derive it, because I really have no idea. 3) When I say a liquid is saturated, it means it's in equilibrium with the vapor, or is it 100% liquid. Then this means the vapor is saturated as well? But there is a graph with P against specific volume that depicts a maximum curve, one of the two sides being the saturated liquid line, and the other being the saturated vapour line and they are not together. Gah please help thanks, I am dying to know.
  4. The MATLAB website states that "the number of arguments is negative if the function has a variable number of arguments" when I use nargin to test such functions. So when I enter nargout ode45, I get -5. But why is the absolute value 5, does that mean it's the maximum number of outputs that ode45 can release? It is not a random number because I keep getting the same result after typing in. Does anyone know why this is happening? Thank you
  5. How do you find this limit? I tried the sin x/x limit, L'Hopital Rule, Taylor Series, but it just kept giving me more sin x and x, so I couldn't get the limit. Can somebody give a clue?
  6. Haha, actually I am a bit confused by what you have said. But I sorta guessed you meant something like configuring, and I didn't know how to configure my compiler until i accidentally went to some website and i solved the problem. Thanks a lot !!! And yes I think I am that sort of person who will find programming fun!
  7. I wrote the following program 01.cpp: //My first program #include <iostream> int main() { std: :cout << "Welcome to C++! \n"; return 0; } The file iostream.h is under C:\Borland\bcc55\Include\iostream.h, while the program is saved under C:\Borland\bcc55. I thought an .exe file was created after doing the following in Command Prompt on Windows. See Picture. cpp32.exe is under C:\Borland\bcc55\Bin\. I included C:\Borland\bcc55\Bin\cpp32.exe under Path in the Environment Variables under Advnaced section of COntrol Panel, so I can call it out anytime. But my exe file is not created. Instead I get an .I file, and I don't know what it is What happened? What went wrong? Sorry this is my first attempt at learning programming, so the way I describe the program may not sound appropriate. Sorry. Thanks in advance!
  8. Is University of Birmingham a really good choice for chem eng? I know it's high in rankings but my friends keep telling me that the program isn't good. How is it compared to University of College London, and Cornell?
  9. A bucket of water is swung in a vertical circle. Explain qualitatively why the water in the bucket does not fall out. My model answer then explained that If the speed of the rotation is high enough, the weight of the water alone in the bucket is not enough to provide for the centripetal force required. A force will be exerted by the bottom of the bucket on the water for the water in the bucket to continue to move in a circle. By Newton's third Law, the water pushes against the bottom of the bucket and thus stays in the bucket. What does the bold text really mean? So what happens if the weight of teh water alone in the bucket is just enough? And if my speed is not high enough, the water flows of the bucket, and what does that mean? Sorry I am really confused. Can somebody clear my confusion? Thanks
  10. Haha yes. I'm going to put on gloves next time; you never know what lurks beneath the mess. T_T
  11. I was looking for some old stuff for my mum through the mess in my storeroom when my finger was drenched in what I later found to be 2-year-old battery leakage. And my finger had an open wound. I washed it off immediately. Will it pose any hazard to my health? Because my mum's uh freaking out a bit lol.
  12. Cute display picture! Haha =D

  13. Initially these blocks of each mass m are at rest. The tabletop and pulley does not induce friction. So when the system moves, does it accelerate at g? Do both blocks have an acceleration of g? Does the weight of the top block affect the acceleration or exert a force on the bottom block? My book says 5 ms-2 and i am puzzled.
  14. easiest to hardest: physics, chem, bio i hate the deducing questions in chem -.- The question can assume a compound with carboxylic, amide and all kinds of functional groups and then state the observations seen after dunking them into a dozen respective chemicals and tell you to deduce the unknown compound from all the observations made. It kills -.- i think physics is relatively easy but still i get Bs all the time. i never take bio. anything you don't study will seem daunting lol.
  15. hello. I am deciding on a major. My A-level subjects are physics, chemistry, math (and chinese literature LOL) and my chem is in the A-B range. But i never went for any research programme, so will it be hard to cope if i take chem engineering? um, and which ChemEng programme is better, Cambridge or UCL? Thank you.
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