VCE Chemistry Question Thread

[Reus]

a thing that has been annoying me, as seen in attachment.
i thought Nitrogen is N? why do they say N2, is it nitrogen gas?

when writing chemical equations and they say hydrogen was produced etc.. do we write H or H2? why and when do we know when to do this

Yes its in a gaseous state hence needs to be N2 in order to react with H2

[Zues]

ok, so what about if it wasnt reacting with H2

say it says nitrogen reacts with...
do we automatically say N2?

[darklight]

Hey guys, just some help with NEAP 2008 qn 2.

I thought that in an equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction . Just clarifying the provided answer of A - isn't R and Q technically being formed/disappearing at the same "rate" but it takes Q four times longer to disappear because there is 4 times as much of it?

[Robert123]

Hey guys, just some help with NEAP 2008 qn 2.

I thought that in an equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction . Just clarifying the provided answer of A - isn't R and Q technically being formed/disappearing at the same "rate" but it takes Q four times longer to disappear because there is 4 times as much of it?

I think this question is fairly ambiguous, however, I believe it is referring to the rate of reaction as it approaches equilibrium so the back reaction has a neglible effect on the rate of formation/disappearing since it is significantly smaller than the forward reaction when it hasn't reached equilibrium.

[Zues]

Do you do gas laws in units 3/4?? If so how much does it differ and get harder compared to year 11???

Thanks

[Reus]

Do you do gas laws in units 3/4?? If so how much does it differ and get harder compared to year 11???

Thanks

I've seen it here and there in the MC section of past VCAA exams.
Unit 3 touches on it, good to retain from year 11 though.
R value is provided in the data booklet thus means examinable.

[lzxnl]

Hey guys, just some help with NEAP 2008 qn 2.

I thought that in an equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction . Just clarifying the provided answer of A - isn't R and Q technically being formed/disappearing at the same "rate" but it takes Q four times longer to disappear because there is 4 times as much of it?

Rate of reaction is different to the rate of formation or rate of disappearance of some quantity. It's defined as essentially the rate of formation of a product (or consumption of a reactant) divided by its stoichiometric coefficient. In your example, the rate of reaction is the same as the rate of production of R, or half the rate of production of S, or a quarter of the rate of consumption of Q.

In this question, let's consider what happens when one molecule of R is formed. You needed two molecules of P and four molecules of Q. Can you see that per reaction, the amount of Q used up is four times the amount of R produced?

[Reus]

The fatty acid with the greatest number of double bonds is:
A. C18H34O2
B. C24H48O2
C. C18H32O2
D. C20H32O2

How do you work this out? :/ Thanks.

[swagsxcboi]

The fatty acid with the greatest number of double bonds is:
A. C18H34O2
B. C24H48O2
C. C18H32O2
D. C20H32O2

How do you work this out? :/ Thanks.

subtract COOH from each molecule
so if you're working it out for A, C18H34O2 will now be C17H33
subtract another H, so you'll have C17H32. then double the number of carbon, 34. 34-32 = 2 H less than if it was saturated. Therefore one double bond

A has one double bonds
B has no double bond
C has two double bonds
D has four double bonds. 

D?

[Reus]

subtract COOH from each molecule
so if you're working it out for A, C18H34O2 will now be C17H33
subtract another H, so you'll have C17H32. then double the number of carbon, 34. 34-32 = 2 H less than if it was saturated. Therefore one double bond

A has one double bonds
B has no double bond
C has two double bonds
D has four double bonds. 

D?

Ah thanks Yep it's D.

[Reus]

Additionally, would it be correct to say that industrial catalysts possess an advantage over biological catalysts as they vary in a range of reactions since enzymes are limited to a specific reaction (due to specificity of active site structure)?

[lzxnl]

Additionally, would it be correct to say that industrial catalysts possess an advantage over biological catalysts as they vary in a range of reactions since enzymes are limited to a specific reaction (due to specificity of active site structure)?

Yeah but...biological catalysts are SO much more effective it's ridiculous.

[Reus]

Yeah but...biological catalysts are SO much more effective it's ridiculous.

Is this why industrial catalysts are usually in powered form?

Haha yes they are I'll just list a few for revision's sake Biological catalysts work under milder conditions and lower temperatures, reused, faster rates (up to 10^10 times more) and are extremely specific (ES complex) 

[lzxnl]

Is this why industrial catalysts are usually in powered form?

Haha yes they are I'll just list a few for revision's sake Biological catalysts work under milder conditions and lower temperatures, reused, faster rates (up to 10^10 times more) and are extremely specific (ES complex) 

Yeah, powdered catalyst => bigger surface area => more useful
It depends on what you're trying to do. Biological catalysts can be ungodly difficult to synthesise in the lab, whereas lots of inorganic catalysts are literally just elemental metals like platinum and rhodium, sometimes complexed with other ligands.

[darklight]

Hi guys

Does the chlorination of an alkEne require a catalyst? Some sources say yes, some say no?

Thanks