VCE Chemistry Question Thread

[ErnieTheBirdi]

Hi Ernie.
I am not doing chem this year but I am doing physics and I know they're obviously very different, but I had a similar experience that I will share. It took me ages to 'get' physics. First SACs were really bad. I just couldn't grasp the concepts. Anyway, I want to say, don't be discouraged by bad scores. I would suggest talking to your teachers. This worked for me. Just tell them where you're at, why your not happy with your results and set a goal and tell your teacher what that goal is. Ask them for their opinion. Ask them what you should do differently to get your goal grade for your next SAC. Make sure they give you specific answers. I found that don't think of the teacher as someone trying to catch you out in SACs and ask questions that you don't know. Because this isn't true. They are there to help. So just communicate with them. Ask things like 'What are you looking for in this question?' 'How can I improve my response on this question?' I know sometimes it is hard to accept that your having trouble in a certain subject. I was so used to acing all my subjects that when I did physics it was extremely hard for me to accept that I sucked at it. I was too proud. It took me ages to actually go up to my teacher and ask for help. But just do it. My last two SACs were A+. Trust me, you'll have their support and your grades will improve.
Hope this helps!

Hey ksel03,
Thanks for your advice , I don't if Quarantine is getting to my head haha. The thing is my teacher is a bit odd, like everyone knows he would give out things people don't know and he doesn't really like his students (at least that's what it seems like). I guess I'll try to talk to him but I don't know to do, I'm actually slightly scared of him. I mean these tests aren't SACs they are only tests and I kind of have a failing average but I don't know how to do better, everyone else seems to understand it so easily and so quickly without effort. It's just such a hard thing to do, you know?

[ksel03]

I completely feel you, and I do totally get the struggle of a bad teacher. Try to look at every test you do and look at every question you got wrong. Sounds obvious ay??? But you'll be surprised at how many people don't do it. You'll be able to see why you got them wrong, and don't forget to note what the right answer is and study that. You'll know exactly what you got wrong and exactly what you need to improve. And don't forget to make a note of it. I literally keep a 'common mistakes book' and for every topic I do, I record any mistakes I made (not only in tests but even practice questions and coursework so you can use it to your advantage in tests as well). Revise this book, the point is that you will know your mistakes inside out and will not remake them.
I totally get not being able to grasp the overall concepts, I feel like it gets easier though. I just used every resource I could (Edrolo, Clickview videos, anything you can get your hands on) because often the textbook (and your teacher) explain things in a complex way that is hard to understand.
Great job, it is awesome to see you have so much determination to improve. Keep working hard, success will come!

[Snow Leopard]

//

Thanks so much for your help Erutepa 
I think I understand how to draw Lewis diagrams now, but I was just wondering, do we have to draw Lewis diagrams following VSPER?

[Erutepa]

Thanks so much for your help Erutepa 
I think I understand how to draw Lewis diagrams now, but I was just wondering, do we have to draw Lewis diagrams following VSPER?

You're most certainly welcome.

When drawing Lewis diagrams you should you should try to show bonds and lone pairs as far away from eachother, but only in 2 dimensions - you won't be showing how bonding occurs in three dimensions (using wedged and dashed lines) like you would when drawing a full VSPER diagrams/molecular geometry. So keep in mind that bonds ans lone pairs will repel eachother, but you don't need to worry about it too much when doing simple Lewis diagrams.

[ErnieTheBirdi]

I completely feel you, and I do totally get the struggle of a bad teacher. Try to look at every test you do and look at every question you got wrong. Sounds obvious ay??? But you'll be surprised at how many people don't do it. You'll be able to see why you got them wrong, and don't forget to note what the right answer is and study that. You'll know exactly what you got wrong and exactly what you need to improve. And don't forget to make a note of it. I literally keep a 'common mistakes book' and for every topic I do, I record any mistakes I made (not only in tests but even practice questions and coursework so you can use it to your advantage in tests as well). Revise this book, the point is that you will know your mistakes inside out and will not remake them.
I totally get not being able to grasp the overall concepts, I feel like it gets easier though. I just used every resource I could (Edrolo, Clickview videos, anything you can get your hands on) because often the textbook (and your teacher) explain things in a complex way that is hard to understand.
Great job, it is awesome to see you have so much determination to improve. Keep working hard, success will come!

Thanks, I will continue to try hard since it is my second last year of high school and all subjects regardless of what unit they are required hard work to do well. To be honest, science was never my strongest field but I'm sure hard work pays off, at least I hope it does. Thanks again for the advice!

[whys]

Hello everyone, I'm a bit confused with the questions I've attached (I guessed the answers since I had no idea haha). Any help would be appreciated!

(The yellow is my answer, and the red is the correct answer)

[Icecream123]

Hello everyone, I'm a bit confused with the questions I've attached (I guessed the answers since I had no idea haha). Any help would be appreciated!

(The yellow is my answer, and the red is the correct answer)

Hmm not too sure about the second question but for the first I think cos it says its unheated were assuming there's no kinetic energy? (and the next best choice is probably surface area haha)

[Geoo]

Hello everyone, I'm a bit confused with the questions I've attached (I guessed the answers since I had no idea haha). Any help would be appreciated!

(The yellow is my answer, and the red is the correct answer)

Hey Whys!
So with 33, dust particles have a really large surface area compared to say a large rock. When the surface area of a solid (the grain particles) is large, then the frequency of collisions increases, which therefore increases the rate of reaction.
So, the more frequent and successful the collisions are, the faster the reaction rate, the more explosive they will be.
So, small objects/particles with have large surface areas, and large objects will have small surface areas. The larger the surface area, the "more room" there is for reactant particles to collide with, this increasing the reaction.
Kinetic energy would only be affected by a temperature change, as kinetic energy is essentially how fast a particle moves, and since the grain particles are just suspended in a silo, and the questions says it is unheated, kinetic energy won't affect how "explosive" it is.

 With question 34, heterogeneous essentially means that the reactions reactants and particles won't all be in the same physical state. The reactant might be a gas, whilst the product is a liquid.
- Temperature won't affect this type of reaction. Think about a gas and a solid reacting, you can heat it up, cause the gas to move faster, but the solid's particles won't move as fast as the gas. So, that wouldn't really affect the rate of reaction.
- Concentrations, same principle as temperature.
- The nature of reactants is implying it's properties, but this won't have an affect on the rate of the reaction.
Surface area really is the only option as if you have a solid and a gas reacting. A larger surface area would mean more gas particles could collide, which would increase the frequency of collisions, thus affecting the rate of reaction. And vise versa for a smaller surface area.
Hope this helps, but I don't know if my explanations are that great for the second question

[Chocolatemilkshake]

With question 34, heterogeneous essentially means that the reactions reactants and particles won't all be in the same physical state. The reactant might be a gas, whilst the product is a liquid.
- Temperature won't affect this type of reaction. Think about a gas and a solid reacting, you can heat it up, cause the gas to move faster, but the solid's particles won't move as fast as the gas. So, that wouldn't really affect the rate of reaction.
- Concentrations, same principle as temperature.
- The nature of reactants is implying it's properties, but this won't have an affect on the rate of the reaction.
Surface area really is the only option as if you have a solid and a gas reacting. A larger surface area would mean more gas particles could collide, which would increase the frequency of collisions, thus affecting the rate of reaction. And vise versa for a smaller surface area.
Hope this helps, but I don't know if my explanations are that great for the second question

For the second, the question says "will affect the rate of heterogeneous reactions only." ONLY is a key world here as it indicates that you should pick a factor which does not influence the rate of homogeneous reactions. So, because changing the nature of reactants, the temperature or concentration of the reactants WILL affect homogeneous reactions these options cannot be selected.

On the other hand, for a homogeneous reactions (which occurs with only liquids or only gases), you can't really "increase the surface area" in order to affect reaction rate and therefore, this option would not affect homogeneous reactions. Increasing the surface area would only have an impact on the rate of heterogeneous reactions involving a solid and hence, you have your answer

Anyway, this is how I interpreted the question but feel free to correct me if I'm wrong
EDIT: stupid mistake and tried to make more clear

[whys]

Hey Whys!
So with 33, dust particles have a really large surface area compared to say a large rock. When the surface area of a solid (the grain particles) is large, then the frequency of collisions increases, which therefore increases the rate of reaction.
So, the more frequent and successful the collisions are, the faster the reaction rate, the more explosive they will be.
So, small objects/particles with have large surface areas, and large objects will have small surface areas. The larger the surface area, the "more room" there is for reactant particles to collide with, this increasing the reaction.
Kinetic energy would only be affected by a temperature change, as kinetic energy is essentially how fast a particle moves, and since the grain particles are just suspended in a silo, and the questions says it is unheated, kinetic energy won't affect how "explosive" it is.

That makes so much sense! I completely neglected the fact that dust particles aren't just gases, but gases adsorbed to solids. Thank you!

Regarding the second question, I get what you guys are saying about the surface area since it applies only to solids, but what if I had a heterogeneous system with liquid and aqueous, or liquid and gas? Wouldn't temperature affect that?

Reread your answer choco - I thought homogeneous reactions were reactions where all reactants + products are in the same state, whereas heterogeneous reactions are ones where reactants + products have different states?

[Chocolatemilkshake]

That makes so much sense! I completely neglected the fact that dust particles aren't just gases, but gases adsorbed to solids. Thank you!

Regarding the second question, I get what you guys are saying about the surface area since it applies only to solids, but what if I had a heterogeneous system with liquid and aqueous, or liquid and gas? Wouldn't temperature affect that?

Reread your answer choco - I thought homogeneous reactions were reactions where all reactants + products are in the same state, whereas heterogeneous reactions are ones where reactants + products have different states?

Haha thanks for that! Yep, that's right.

What I'm trying to say is because temperature ALSO affects homogeneous reactions then it cannot be the answer because the question asks for what factors will only affect the rate of the heterogeneous reactions and not the rate of a homogeneous reaction. Because surface area can affect some heterogeneous reactions (the ones that involve solids) then it is the correct answer because surface area will never be able to affect the rate of any homogeneous reaction. I'm probably reading it wrong though and if I am, I'd love to know what the correct way to interpret this question is.

[whys]

Haha thanks for that! Yep, that's right.

What I'm trying to say is because temperature ALSO affects homogeneous reactions then it cannot be the answer because the question asks for what factors will only affect the rate of the heterogeneous reactions and not the rate of a homogeneous reaction. Because surface area can affect some heterogeneous reactions (the ones that involve solids) then it is the correct answer because surface area will never be able to affect the rate of any homogeneous reaction. I'm probably reading it wrong though and if I am, I'd love to know what the correct way to interpret this question is.

Ohh I see now, thanks! No, you seem to be reading it correctly to me.

Thanks everyone!

[Erutepa]

Hello everyone, I'm a bit confused with the questions I've attached (I guessed the answers since I had no idea haha). Any help would be appreciated!

(The yellow is my answer, and the red is the correct answer)

For the second reaction regaurding heterogenous reactions, I definently agree with chocolatemilkshake's explanation: that question wants you to identify that homogenous reactions will only occur between gasses or between liquids, thus there isn't really a surface area to consider, thus meaning surface area is only really a factor when it comes to heterogenous reactions. While in actuality homogenous reactions can infact happen between two solids, in which case the surface area of reactants do matter for some homogenous reactions, for the purpose of VCE chemistry I think it is probably OK to ignore such reactions. As a side note, the chem study design doens't really refer to needing to know how to distinguish between homogenous/heterogenous reactions and i had never come across a question asking you to, so I thinks its fairly unlikely that you will be asked a question similar to this in an exam.

[amanaazim]

hey, can someone help me with these questions please.

What is the mass of the following?

A) 5.25x10^24 molecules of glucose , c6h1206
B) 1.83x 10^21 molecules of nitrogen dioxide, NO2
C) 3.56x 10^24 molecules of carbon dioxide , CO2
D) 4.13 x 10^28 molecules of carbon disulfide, CS2
E) 3.62 x 10^24 molecules of dinitrogen tetroxide, N2O4

With working out please

[whys]

hey, can someone help me with these questions please.

What is the mass of the following?

A) 5.25x10^24 molecules of glucose , c6h1206
B) 1.83x 10^21 molecules of nitrogen dioxide, NO2
C) 3.56x 10^24 molecules of carbon dioxide , CO2
D) 4.13 x 10^28 molecules of carbon disulfide, CS2
E) 3.62 x 10^24 molecules of dinitrogen tetroxide, N2O4

With working out please

First, use the formula n = N/NA where n is moles, N is the number of particles and NA is Avogadro’s number. Once you have the number of moles, sub it into the formula n = m/M where n is moles, m is mass in grams and M is molar mass. This should help you solve all the above questions.