HSC Chemistry Question Thread

[RuiAce]

hi, does changing concentrations of products/reactants have any effect on reaction rate in an equilibrium reaction, or does it only impact yield?

Whether or not it impacts on the rate is outside the scope of the HSC. We only care about yield.

You could logically infer what happens; in every typical equilibrium graph if a substance is made more concentrated then initially it gets used up more rapidly. And in fact, the more you add in, the more rapid it is at the start. But then you just can't say for sure what happens.

[nimasha.w]

hey! i don't understand this question

[RuiAce]

hey! i don't understand this question

Hint: Look at the table of standard reduction potentials, and decide if the equation was written correct or possibly mistakenly written backwards for a galvanic cell.

Only the correct galvanic cell equation will occur spontaneously. The wrong equation only occurs in an electrolytic cell and that's NOT spontaneous.

[angiezhang9]

Is there a difference between how a transuranic element and a commercial radioisotope is produced? My understanding is that they're both produced by firing neutrons in a nuclear reactor or by bombarding with a charged particle in an accelerator.

[RuiAce]

Is there a difference between how a transuranic element and a commercial radioisotope is produced? My understanding is that they're both produced by firing neutrons in a nuclear reactor or by bombarding with a charged particle in an accelerator.

Yeah not really, they're pretty much produced the same way. They're just two dot points because you need to be prepared to give examples for each.

[wesadora]

Is there a difference between how a transuranic element and a commercial radioisotope is produced? My understanding is that they're both produced by firing neutrons in a nuclear reactor or by bombarding with a charged particle in an accelerator.

Yeah nerd you gotta know examples for every one 

[wesadora]

When sodium hydrogen carbonate acts to neutralise an acid (and considering the amphiprotic nature of HCO₃^-,
I don't understand how this equation is valid, ...I mean, the H30+ does donate a proton, but another acid (H2CO3) is created anyway? How is this 'neutralisation', or is this equation even good to use in an answer of why NaHCO3 is suitable for cleaning up acid/base spills? I'm pretty sure it is though, seen it in HSC suggested answers. Just don't understand what's up with h2co3...(carbonic acid)

[RuiAce]

When sodium hydrogen carbonate acts to neutralise an acid (and considering the amphiprotic nature of HCO₃^-,
I don't understand how this equation is valid, ...I mean, the H30+ does donate a proton, but another acid (H2CO3) is created anyway? How is this 'neutralisation', or is this equation even good to use in an answer of why NaHCO3 is suitable for cleaning up acid/base spills? I'm pretty sure it is though, seen it in HSC suggested answers. Just don't understand what's up with h2co3...(carbonic acid)

Neutralisation just means acid + base. It doesn't always give you something with a pH of 7.

Note that BY DEFINITION, according to B-L theory, an acid is a proton DONOR and a base is a proton ACCEPTOR.


The whole point of NaHCO3 in neutralisation of spills is that we have a WEAK acid/base remaining, not a STRONG one.

[wesadora]

Neutralisation just means acid + base. It doesn't always give you something with a pH of 7.

Note that BY DEFINITION, according to B-L theory, an acid is a proton DONOR and a vase is a proton ACCEPTOR.


The whole point of NaHCO3 in neutralisation of spills is that we have a WEAK acid/base remaining, not a STRONG one.

OHHHHHH that makes so much sense. Thanks Rui.

[massive]

is there a difference between petroleum and crude oil?

[RuiAce]

is there a difference between petroleum and crude oil?

Crude oil is the rest of the mixture. Petroleum is the actual hydrocarbons we use from the mixture.

But these terms get used interchangeably too often and nobody cares if you get them confused.

[Neutron]

The NaOH drives the reaction to completion.

Recall that only the reaction between a weak base and an weak acid is reversible, i.e. it goes into equilibrium. The presence of at least one of a strong acid, or a strong base, will force the reaction to go to the end.
This is because, in the case that both substances are partially ionised (weak), there's only so many H⁺ and OH^- to react. So this system will stabilise out. Whereas if you have something strong, the NaOH here, the presence of the OH^- ions will continuously drive the equilibrium (by LCP) so that the reaction ultimately goes to completion.

We note that the concentration of NaOH and both the volume AND concentration of the acids have been fixed. So the fact that we have all those OH^- there from the NaOH will drive the reaction regardless of the acids. Hence, if the same outcome is to be achieved, the last thing to be fixed is the volume of NaOH. Yes

But even if it 'drives it to completion' wouldn't you still only need less OH- to completely neutralise the weak acid?

[onepunchboy]

Can anyone explain why water samples taken from a fast-running stream and from a swap differ in oxygen concentrations? thanks ))

[onepunchboy]

Also im not sure how to do this q, sry about asking so many q haha... thanks

[nimasha.w]

hey! can i please have some help with these questions :-)