stonecold's chem questions :)

[stonecold]

And Insight says the answer for this is not D. 

[stonecold]

Insight said it was option B.  How can increasing the concentration increase rate of reaction, but increasing the surface area doesn't?  They both do the same thing.  Make more particles available to react, hence more successful collisions, and blah blah, you all know the collision theory.

[superflya]

ahahahah just deleted my post after reading it again and realising it was complete nonsense.

but im pretty sure all those options increase rate :/

[stonecold]

lol, i'll delete the quote for you

[Whatlol]

I think its like this. You can keep increasing surface area but that doesn't necessarily increase number of reactions because imagine a scenario where there is already a maximum number of particles reacting, say x /x particles are reacting. You then proceed by increasing the surface area. still x/x particles are reacting and nothing changes.
I hope that makes sense, hard to explain i think its correct tho (=

EDIT : ok maybe that doesnt work ....  
maybe i should add that when i say maximum number of particles reacting, i mean the maximum number of particles with a sufficent energy to react are already reacting

[fady_22]

Increasing the surface area only works with solids, and so this change does not ALWAYS increase the reaction rate.

[iffets12345]

^ what fady said...
just as concentration wouldn't work for solids, I think, or pressure only works with gas pretty much.

[fady_22]

^ what fady said...
just as concentration wouldn't work for solids, I think, or pressure only works with gas pretty much.

In VCE, reactions between solids do not exist. So you can always increase concentration (of a gas or solution).

[stonecold]

For question 5, I keep getting 200g, but the answers say it is 57g.

I have spotted an error in their calculations though, but still not sure I have the right answer...

If someone could do it, that would be great.  It is down the bottom of the previous page.

[Studyinghard]

What exam is this ^^. i dont even know how to do 5a =\

[stonecold]

Insight 08.  It is available in that thread with all the chem exams.

[iffets12345]

For question 5, I keep getting 200g, but the answers say it is 57g.

I have spotted an error in their calculations though, but still not sure I have the right answer...

If someone could do it, that would be great.  It is down the bottom of the previous page.

I got this answer too, there's a mistake in the working out I believe, where they didn't half or double the octane/whatever it was since it was 2 mol in the equation so the enthalpy should have been halved.

[stonecold]

thanks iffets!  we're not going to fail chem after all

[iffets12345]

lol *crosses fingers*.

[stonecold]

How does this question work...  I get that that self ionization of water is endothermic so as temp increases above 25C, pH decreases, and if temp is below 25C, pH increases.

I know it has something to do with it.  STAV Explanation sucked.  From 2008 btw.