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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: donkey on July 25, 2010, 01:48:05 pm

Title: Chemistry Unit 4 ~ Help questions.
Post by: donkey on July 25, 2010, 01:48:05 pm: Hi.
Can I have some help with these?
Thank you.

Mod Edit: Thread title changed to make the thread clearer.

- Gloamglozer

Mod Edit: Thread title changed to the correct subject.

- Mao

Donkey Edit: Thread title changed to further correct the subject
Title: Re: Electrolysis & Energy Profile Help
Post by: Whatlol on July 25, 2010, 04:49:52 pm: (http://img806.imageshack.us/img806/7761/chems.png)

For the reaction = $Cu2O + \frac{1}{2}O2 \rightarrow 2CuO \Delta H = - 142 kJmol^-1$ (this is because the first reaction had $-170 kjmol^-1 :.$ enthalpy will be $312-170 = 142kjmol^-1$

the reverse reaction is $2CuO \rightarrow Cu2O + \frac{1}{2}O2 \Delta H = + 142 kJmol^-1$

But since they have doubled the coifficents, the enthalpy will be doubled.

$4CuO \rightarrow 2Cu2O +O2 \Delta H = + 248 kJmol^-1$
Title: Re: Electrolysis & Energy Profile Help
Post by: donkey on July 25, 2010, 11:06:04 pm: Thank you Whatlol. Any idea about the half cell one?
Title: Re: Electrolysis & Energy Profile Help
Post by: Whatlol on July 25, 2010, 11:07:45 pm: Quote from: donkey on July 25, 2010, 11:06:04 pm
Thank you Whatlol. Any idea about the half cell one?

I would help but i havent covered the theory for it, and i have limited knowledge of it from last year so i dont want to confuse you. sorry.
Title: Re: Electrolysis & Energy Profile Help
Post by: vexx on July 25, 2010, 11:21:53 pm: ^ In Galvanic cells, where oxidation is the Anode and occurs at the negative terminal, and where reduction is at the Cathode at the positive terminal. Each reaction is separate as there are four done, so for each of the reactions, you can see that the positive electrode (being the cathode in galvanic cells only) will be where the strongest oxidant is, and the anode will have the strongest reductant.
Like for I and IV reacting, P(+) is the stronger oxidant and Cu(-) is the stronger reductant.
Just use that info. to make a list of what beats what and you'll get the right answer.

the edited title is wrong btw, this is galvanic cells, not electrolytic.
Title: Re: Galvanic Cell & Energy Profile Help
Post by: donkey on July 31, 2010, 12:49:29 pm: Thank you Vexx.

At what stages of the contact procress is the H2SO4 a liquid, and when is it aqeous?
Title: Re: Chemistry Unit 4 ~ Help questions.
Post by: donkey on August 05, 2010, 08:06:08 pm: Also, in the 2008 CHEM exam 2 short answer section: the value in JKmol-1 of deltaH for the reaction written is asked for. Where is this knowledge supposed to come from? Is this part of a number of deltaH values we should memorise from the book? Upon looking at my book to see for this information I found data that was slighty off the examiners solution so I don't know where this answer should have come from since I can't see how it comes from the data.
Title: Re: Chemistry Unit 4 ~ Help questions.
Post by: andy456 on August 05, 2010, 08:08:07 pm: Without seeing the exam, Theres a section in the hienmann textook on thermochemical equations and im pretty sure it shows how to find deltaH