Unit 4 questions

[bec]

Right, got it. So with pressure, the change in reaction quotient IS instantaneous - because both reactants and products go up by a constant pressure which throws them out of their equilibrium ratio. Which, come to think of it, I've known all along.
But when you put it like that it all makes a lot more sense, and yay I think I understand the temperature/K thing now...thanks Coblin!

[Collin Li]

No problem

[bec]

A faraday is 96500C isn't it?
...."passage of 0.10 faradays of electricity through an aqueous tin chloride solution deposited 5.94g of tin at one electrode..."
does this mean that n(e)=0.1?

[Collin Li]

Yes.

Don't be confused by the difference between "a Faraday" (charge) and "Faraday's constant" (charge/amount)

[bec]

Yeah, that's what was confusing me! Thanks Coblin.

[bec]

How do catalysts work? ....to a VCE chem level?

Just did a question asking for the effect of a catalyst on the activation energy, and my response was:
It will lower the activation energy: catalysts attract the reactant which breaks its bonds in order to bond to the catalyst's surface.

The answer in the solutions was: a catalyst decreases the activation energy by providing an alternate reaction path.

So... 1) am I right in what I said and 2) do you think all we need to know in the new course is that catalysts "provide an alternate reaction path"?

Thanks

[Mao]

I think they prefer "alternate reaction pathways" more

from what my teacher's told me, catalysts have higher surface energy, which does something or rather that we don't need to know...

[bec]

Sounds good...

[Collin Li]

What you describe is correct for some types of catalysis (heterogenous, i.e: surface and gases), but the general answer is that it provides an alternate reaction pathway.

[bec]

Question; in the data booklet, do the molar enthalpies of combustion assume that water is liquid or gaseous?
In the Heinemann textbook, there's a question asking to write an equation to represent the reaction of ethanol, and they've written
In the data book, of ethanol is -1364 so I'm assuming it refers to liquid there. So, is it always liquid?
I know there's a column for "state" but that doesn't refer to the state of water (unless combustion of glucose gives ice...)

[Collin Li]

If they don't give you enough information, just assume whatever the data book says and don't worry about states.

Standard heats of combustion are standardised to 298K and 1 atm, so water should be in a liquid state... I think.

[bec]

Is it just me or is this question bizarre?
The answer is B
I don't understand why it can't be D as well...

[bec]

sorry to be a pain, but...anyone?
This is from the VCAA 2000 exam 1

[Mao]

no idea of it's relevance, but most [all?] spontaneous reactions are exothermic

though it says "of the reaction", is there a reference to a previous reaction?

[bec]

Ahh yeah very perceptive mao, you were right - it referred to an exothermic reaction it had already given. (the question was given to me in isolation though, which is why I didn't pick that up)
Thanks