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OCR AS - Chemistry Unit F322 - Chains, energy and resource - REVISION!

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Reply 600

lolo-x

Original post by Rassam

Enthalpy change: when is it products minus reactants and reactants minus products??

draw a Hess cycle :smile:

http://www.chemguide.co.uk/physical/energetics/sums.html

Reply 601

touran22

i just chedcked in the mark schemes and they give full marks for the answer with no working out!

Reply 602

lolo-x

Original post by arvin_infinity

Hess law defi !?

Hess' law: overall enthalpy change for a reaction is the same, irrespective of the route taken (as long as conditions are the same)

Reply 603

patra

Original post by lolo-x

Percentage Yield: actual moles of product obtained divided by the expected moles of product all multiplied by 100

Atom economy: Mr of desired products divided by the sum of Mr of all products x 100

Percentage yield is really how efficiently the reaction is taking place - is the reaction operating at its maximum potential?

Atom economy shows you how much useful product you are getting out of all of the products you have got, so it shows you how wasteful your reaction is :smile:

thanks a lot, that makes sense! :biggrin:

Reply 604

touran22

guys can we say Ea instead of activation energy in the exam?

Reply 605

arvin_infinity

Benefits of
isomersation
reforming
cracking
??

Reply 606

patra

can anyone explain what Ziegler Natta is? what do we need to know abou it?

Reply 607

yesioo

Hess's Law is killing me.

Anyone got any links for Green Chem + Boltzmann?

Reply 608

TaRhaR

Where it doesn't specify how to draw a compound, shall I just draw the displayed formula?

Reply 609

simple_gurl

How do you find the enthalpy change of formation when they give you the data for enthalpy change of combustion and vice versa?

Reply 610

lolo-x

Original post by patra

can anyone explain what Ziegler Natta is? what do we need to know abou it?

all it says in the spec is that you should know that the catalyst for polyethene production is ziegler-natta :smile:

Reply 611

lolo-x

Original post by yesioo

Hess's Law is killing me.

Anyone got any links for Green Chem + Boltzmann?

my notes?

CHEMISTRY UNIT 2.doc332.8KB

Reply 612

lolo-x

Original post by touran22

guys can we say Ea instead of activation energy in the exam?

i'm not sure, best not to, just in case :smile:

Reply 613

arvin_infinity

Original post by patra

can anyone explain what Ziegler Natta is? what do we need to know abou it?

Ticl3
60 degrees
Unbranched polymer ..thats all I remember

good luck guys!

How well do we need to know the Other uses of Polymer wastes (i.e. Feedstock recycling )?

Reply 616

arvin_infinity

iii) Outline 2 examples where C02 has replaced the need for CFC's.
• v) What is the method of obtaining decarbonised fuel and show an equation for methane.

??

Reply 617

patra