I'm confused about the first few dot points in POM (1 Viewer)

[fatassmcfat]

1) When you have ethene + X = Y, will Y be called (Xethene) or (Xethane)? Because its become saturated, so shouldnt it be called Xethane? or do you retain the name of the original hydrocarbon ethene?

2) Say you have polyethene chain, and it consists of 3 ethene monomers. So the name of it is C6H14- but isnt that hexane? Or is hexane a type of polyethene chain? But then at the same time I'm confused- cause shouldn't a polyethene chain never end since each monomer only has 4 H's (and on the first and last monomer of this chain you would need 5 H's to complete it)?

3) what is the major source of ethene according to the syllabus/what the markers wanna know? (my teacher said thermal cracking, conquerinq chem says steam cracking and some places say steam/thermal are the same thing)

Also does anyone know if theres a set percentage of the HSC exam which requires calculations in proportion to writing bits (im assuming quite a lot since chem is good scaling)?

THANKS

 

[fatassmcfat]

Also for 3) some places same catalytic cracking

 

[joelferns27]

The major source of ethylene is from the cracking of the fractions of crude oil. This is done through catalytic cracking (using zeolites, atmospheric pressure, 300 degrees, no oxygen) or through thermal cracking (hydrocarbons passed through steam 1000 degrees and NO catalysts).

And ethylene can undergo addition reactions or substitution reactions. But having saying that, it cant react with everything as you know not everything reacts with everything, unless of course you apply enormous amounts of energy.

HSC CHEMISTRY EXAM: 30% theory 30% calculations 15% prac 15% discriminators

 

[strawberrye]

1) Have a look at this link: http://www.chemguide.co.uk/organicprops/alkenes/halogenation.html . Your question is a bit too broad-because ethene can undergo different reactions according to the other reactant, say if Y was another ethene molecule, then your product would be polyethene. For another example, if Y is a bromine molecule, then the reaction with ethene would product 1, 2-dibromethane as a product. If Y was bromine water, HOBr, then the product can be 2-bromoethanol. So you see the product name is dependent on what your reactants are.

2)How is 3 ethene monomers combine to form C6H14? There is no H at the end of the chain, it is a repeating unit, a better formula to represent would be the image at the top right hand corner, http://www.graylineinc.com/tubing-materials/polyethylene.html where n is 3. Since ethene is a repeating unit, the H at the end is not a part of the repeating unit, and hence the formula for 3 ethene monomers added together is different from hexane or hexene(there is no presence of a double bond)

A polyethene chain does end. Every chemical reaction needs energy of some form to proceed-hence the heat required for polymerisation process to start, if you stop adding in energy, i.e. stop heating, then the reaction will not have enough activation energy to proceed. Remember the law of energy conservation: energy cannot be created or destroyed. Remember that additional polymerisation is not just a simple linear breaking of double bonds and adding molecules. For LDPE production process, when you use a peroxide initiatior to produce peroxide free radicals which combine with ethene monomers in the process of activation. The activated monomers react with additional ethene monomers to increase chain length in a process of propagation. THE KEY POINT TO REMEMBER IS THAT THERE IS MORE THAN ONE FREE RADICAL PRODUCED-notice the plural of radicals, so there will be chains of variable chain length formed, the polythene chain stops when the various chains combine to form non-activated species. Addition of inhibitors or lowering the pressure and temperature can also impede the polymerisation process. For the HDPE process, reaction conditions can be varied to control the molar weight, and hence chain length of the HDPE is definite-but the length is variable.

3)The relevant dot point in the syllabus is Identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum, I believe learning about the catalytic cracking and thermal/steam cracking process is the two main ones you should be concerned about. Steam and thermal cracking are the same thing, reason being thermal cracking for ethene involves using steam as an inert diluent which allows the process to operate just above atmospheric pressure and reduce concentration of reacting gas to ensure only the desired reaction(s) occur

I think what joelferns27 stated as the percentage composition of a typical HSC chemistry exam is about right. Hope this clears some things up and if you have any more questions on chemistry, you are more than welcome to PM me and ask Best wishes for you to have an enjoyable and productive holiday

 

[fatassmcfat]

WOW THANKS AGAIN I actually get it now... Btw what is the 'discriminator'?

 

[strawberrye]

WOW THANKS AGAIN I actually get it now... Btw what is the 'discriminator'?

I think the 'discriminator' is referring to those particularly difficult multiple choice questions that are used to differentiate the top band students from other bands, and the 5/6/7/8 markers that are used to differentiate band 6s from band 5s due to how well students answers these high mark responses.

 

[joelferns27]

Discriminators are those questions that are "unseen" (ie. basically ones you've never seen before) and only having a good understanding of the concepts will get you through it. In multiple choice however, they cant really distinguish between band 5 and 6. THe only thing about multi choice is that there are sometimes 2 correct asnwers but the most correct one is the answer, so thats what makes it a bit harder i guess.

ps. good work gettin 94 in chem strawberrye

 

[strawberrye]

Discriminators are those questions that are "unseen" (ie. basically ones you've never seen before) and only having a good understanding of the concepts will get you through it. In multiple choice however, they cant really distinguish between band 5 and 6. THe only thing about multi choice is that there are sometimes 2 correct asnwers but the most correct one is the answer, so thats what makes it a bit harder i guess.

ps. good work gettin 94 in chem strawberrye

Thanks for supplementing my answer Thanks for the praise-but I really think at the end getting 94 in chemistry-it is just a mark-it doesn't really say much about how much I love chemistry and how much I do enjoy helping others with the subject. And I am sure that anyone, with enough dedication, passion and faith can exceed that mark

 

[joelferns27]

Yeah i feel the exact same way about it and physics too, but sometimes you fear that your passion might not be good enough you know? but yes definitely dedication passion and faith will get you there ! But i must say, there are somethings you just need to memorise and it amounts to a lot of memorisation.

 

[Essay Questions]

The major source of ethylene is from the cracking of the fractions of crude oil. This is done through catalytic cracking (using zeolites, atmospheric pressure, 300 degrees, no oxygen) or through thermal cracking (hydrocarbons passed through steam 1000 degrees and NO catalysts).

And ethylene can undergo addition reactions or substitution reactions. But having saying that, it cant react with everything as you know not everything reacts with everything, unless of course you apply enormous amounts of energy.

HSC CHEMISTRY EXAM: 30% theory 30% calculations 15% prac 15% discriminators

What do you mean by discriminators?

 

[strawberrye]

What do you mean by discriminators?

If you read the replies to this thread very closely-you will find your answer