VCE Chemistry Question Thread

[Vaike]

Hey!!
"NOTE: Changing the pressure of chemical reactions involving liquids and solids won't result in an increase in reaction rate."
I don't understand what this means . .Can someone please explain?

Hi! Eric11267 hit the nail on the head really. In general, pressure only ever really refers to gaseous systems in VCE. Take a look at this diagram:
As shown, solids and liquids are both packed together very tightly. This results in them being almost incompressible, and hence, increasing pressure doesn't result in an increased collision frequency. Conversely, particles in a gas have large amounts of space in between them, hence a gas can be compressed. Thus, increasing pressure, whether it be through increased temperature or decreased volume, will increase the collision frequency between reactants, increasing the amount of successful collisions, and hence result in an increased reaction rate.

[vcestressed]

Makes so much more sense now! Thanks guys!

[vcestressed]

Can someone please help me with this and run me through their thinking process while doing this question?
All I've picked up in this question is that it is an endothermic reaction and that the moles are different in the LHS and the RHS of the reaction.
Thank you so much.

[sweetiepi]

Can someone please help me with this and run me through their thinking process while doing this question?
All I've picked up in this question is that it is an endothermic reaction and that the moles are different in the LHS and the RHS of the reaction.
Thank you so much.

As the reaction is endothermic, high temps shift the equilibrium to the right, which increases the yield
As there is more moles on the right, a pressure increase shifts the equilibrium to the left, which decreases the yield.
Therefore, the answer should be D.

[Bri MT]

Can someone please help me with this and run me through their thinking process while doing this question?
All I've picked up in this question is that it is an endothermic reaction and that the moles are different in the LHS and the RHS of the reaction.
Thank you so much.

When you have a reversible reaction, the extent to which the forward and reverse reactions occur shifts to partially oppose changes in the environment.

So when you increase the temperature of the environment the system of equations wants to decrease it.
It does this by favouring the endothermic reaction
The forward reaction is endothermic
Therefore the value of the equilibrium constant is increased.

When you increase the pressure the system of equations wants to decrease it.
It does this by favouring the reaction which produces fewest mols
The reverse reaction produces fewest mols
Therefore the value of the equilibrium constant is decreased



Have you studied Le Chatliers Principle?

[Azim.m]

Just wanted to ask, Is it recommended to finish the whole chemistry course throughout the summer break? i'm motivated and adamant on putting the effort but i'm just concerned whether it's worth it or not.

Thanks in advance

[chooby]

Just wanted to ask, Is it recommended to finish the whole chemistry course throughout the summer break? i'm motivated and adamant on putting the effort but i'm just concerned whether it's worth it or not.

Thanks in advance

Is this your only 3/4 this year? If it is, hell yeah go for it but don't forget to keep up with holiday homework for your 1/2's so you don't fall behind. If this isn't your only 3/4 I wouldn't recommend because you'd have to balance it out with your other 3/4s so you don't fall behind everything. I would suggest going through AOS1 and possibly AOS 2 in detail so that way you're prepared for your SACs and are still ahead.

[Bri MT]

Just wanted to ask, Is it recommended to finish the whole chemistry course throughout the summer break? i'm motivated and adamant on putting the effort but i'm just concerned whether it's worth it or not.

Thanks in advance

It's not standard procedure or necessary. It's certainly not worth burning out, if you feel that that might be a risk. I think it's worth sending an email to the teacher you'll have next year and hearing their thoughts on this.

If you do decide to prelearn the course make sure that when you are at school you stay engaged and pay attention to details such as word choices rather than just going "nah I've already got this" mentally.


Nice dedication level btw, good sign

[vcestressed]

When you have a reversible reaction, the extent to which the forward and reverse reactions occur shifts to partially oppose changes in the environment.

So when you increase the temperature of the environment the system of equations wants to decrease it.
It does this by favouring the endothermic reaction
The forward reaction is endothermic
Therefore the value of the equilibrium constant is increased.

When you increase the pressure the system of equations wants to decrease it.
It does this by favouring the reaction which produces fewest mols
The reverse reaction produces fewest mols
Therefore the value of the equilibrium constant is decreased



Have you studied Le Chatliers Principle?

Sorry, I just saw this now! Your explanation makes sense, thank you so much.
I have studied Le Chatlier's Principle, i really have to brush up on it again

[vcestressed]

For the structures of protein (primary, secondary, tertiary & quaternary), do we need to know in particular which important attractions (e.g H bonding, disulfide bridges) hold the structures together and where in the structure?

[sweetcheeks]

For the structures of protein (primary, secondary, tertiary & quaternary), do we need to know in particular which important attractions (e.g H bonding, disulfide bridges) hold the structures together and where in the structure?

From looking at the study design I would say that you would likely need to know some basic information. It's not too difficult. Just remember that the primary structure is the sequence of amino acids, which are joined together through peptide bonds. Secondary structure is the formed from the interactions between the C=O and N-H bonds of different peptide bonds. Tertiary structure is the interactions between side chains of the amino acids (R groups) and includes disulphide, ionic, hydrogen, dispersion. Quaternary is when you have two seperate chains bonded together, and these bonds are the same as the ons that contribute to the tertiary structure.

[vcestressed]

Can someone please help me with this question and explain how they got the answer? Thank you so much.

[Syndicate]

Can someone please help me with this question and explain how they got the answer? Thank you so much.

For the first row, it says the metling point is very high, which means the intermolecular bonding must be really stong, hence it cannot be a convalent molcule (it is the wekaest one out the four). In the next coloumn, it says that the conductivity is very low, hence it cannot be an ionic compund or a metal (both are highly conductive), which means it's a convalent network, which makes sense (think of a diamond).

For the second row, the melting point is very low, this means it cannot be a metal, an ionic compound or a convalent network. This must be a convalent molecule, as it has a low electrical conductivity in its solid and liquid form (very less delocalised electrons). Note: it cannot conduct electricity in its gas form, as the molecules are so far dispersed.

I hope this is enough to start you off 

[vcestressed]

Hey! Thanks for that. Do these answers look right? (Still unsure about the last one!)

[sweetcheeks]

Hey! Thanks for that. Do these answers look right? (Still unsure about the last one!)

They look correct to me.

The last one is a bit difficult. I believe that it is referring to covalent network, something like graphite. It follows the same style as the example, except that this one has a high conductivity.