HSC Chemistry Question Thread

[MisterNeo]

when doing calculations involving heats of combustion and specific heat capacities, should we always use J/kg/K because that is what is given? and how do you convert something that is in kJ/g/K to J/kg/K? thanks so much in advance, I really appreciate all the help here!

For me, ΔH is always in joules, and for specific heat capacity of water (C) I just plug in 4.18 without any units (it's 4.18J/degree).
If your C is in kJ/degree (0.00418kJ), your ΔH must be in kJ. You just divide/multiply by 1000 since there are 1000J in 1kJ.

[liya1234]

For me, ΔH is always in joules, and for specific heat capacity of water (C) I just plug in 4.18 without any units (it's 4.18J/degree).
If your C is in kJ/degree (0.00418kJ), your ΔH must be in kJ. You just divide/multiply by 1000 since there are 1000J in 1kJ.

okay thank you!! also then do we not need to consider whether it is g or kg as long as we use the same unit throughout?

[bsdfjnlkasn]

Help please

[MisterNeo]

Help please

[winstondarmawan]

Hello!
For membrane filters, is it necessary to know the three types and their specifics (i.e. micro, ultra and nano)?

[MisterNeo]

Hello!
For membrane filters, is it necessary to know the three types and their specifics (i.e. micro, ultra and nano)?

Yeah, i would know them because they may ask something like “explain the use of membrane filters...”, which would require the 3 filters. Also note their pore sizes and what things they block (pathogens, suspended solids, etc).

[Noorijaz]

for calcs

is it the minimum number of sig figs in queation or max number of sig fig in question , which we address our answer to.

[Natasha.97]

for calcs

is it the minimum number of sig figs in queation or max number of sig fig in question , which we address our answer to.

You would change your answer to the least number of significant figures, e.g. if they gave you a question that had two values, one with 4 and one with 2 sig figs, change it to 2

[ilovemycat]

Hi, could someone please help me with this question on heat of combustion? Im getting a ridiculously small number (0.000001287) and im sure its not right   .  i always get confused when they ask "x% is lost to the surroundings" with these questions..

Thank you

[Natasha.97]

Hi, could someone please help me with this question on heat of combustion? Im getting a ridiculously small number (0.000001287) and im sure its not right   .  i always get confused when they ask "x% is lost to the surroundings" with these questions..

Thank you

Hi!




Hope this helps

Edit: Fixed latex

[ilovemycat]

hey, thanks so much for that. just wondering where you got the "0.0835" from?

[jakesilove]

hey, thanks so much for that. just wondering where you got the "0.0835" from?

Hey! To find the number of moles of Ethanol, Jess has divided the Energy that was RELEASED by the energy that WOULD BE RELEASED if one mole of Ethanol was burned. ie. 57.057/683.5= 0.0835. It's definitely a weird step, but one that you'll get super used to

Jake

[itssona]

can someone pls check my answers :/
CH3CHOHCH3
is that 2-propanol?

CH3CH2CHOHCH2CH2CH2OH
1,4-hex diol??
how do we draw this
also how do we do q4 from the 2005 hsc
https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2005exams/pdf_doc/chemistry_05.pdf

Mod Edit: Post merge.

[mxrylyn]

Hey!

So I'm looking at the syllabus dot point which states Explain what is meant by a condensation polymer

I understand that a condensation polymer is a polymer (long chain molecule) formed when pairs of monomers join and a small molecule (usually water) is eliminated.

but I don't understand the statement "Condensation polymers are made from monomers that have two different groups of atoms that can join together"

*I put the bit I don't understand in bold

also, does
"One or two types of monomers can be involved and no double bond is required – the bond forms where the molecule is eliminated."

mean that there cannot be three monomers? Also does it also mean that alkanes can form condensation polymers?

I'm also not really sure what is being addressed in this statement

"The end product of condensation polymerisation depends on the number of functional end groups of the monomer that can react. If there is only one reactive group the growing chian will terminate. With two reactive end groups a linear polymer if formed. with three or more reactive end groups a three-dimensional, cross0-linked polymer can be made"

^This is a statement I have memorised, but I have no idea what it means. My main problem is that I don't understand/am not used to the terminology.

Do we need to know about the formation of Nylon and Kevlar in the syllabus dot point Describe the reaction involved when a condensation polymer is formed ?

When they say that, do they mean we need to be able to describe where the small molecule splits out and where the new bonds are formed?
Mod Edit: Post merge.

[itssona]

would someone be able to illustrate using an example, how we use activity series to figure half equations of displacement redox stuff? thank you