Molar heat of combustion vs. Molecular weight. (1 Viewer)

[dwatt]

Well...I'm not so sure about this question. It does to be more than a co-incidence that the people who chose to start from methanol obtained a straight line through the dots. I also read it as starting from 0 (though I think that's incorrect in hindsight).

I felt confident in using a line of best fit because the following question (about deviation from expected values) implied that there was something iffy about the method, so I thought it was ok that they didn't match up!

Ah well - can't do anything about it now.

 

[ravdawg]

THere was no need to put your line through the origin as the smallest mass of an alkanol is meth. I did a line of best fit with crosses and started my graph from meth up, the line doesnt mean anything for any mass less than meth, but then again it doesnt mean anything for values in between meth- eth, eth-pro etc.
So i dunno, i dont think we were meant to graph thru origin anyway, because it wouldve screwed the gradient of the graph.

 

[chocolate_lover]

I picked the first one in the poll - Plotted values as crosses and used line of best fit.

my line of best fit went in perfectly, it was a straight line passing through all the points

Same here. :uhhuh:

I got 1700 too and I did the first one in the poll

I might've got that... it kinda rings a bell. (lol, I don't really remember).

 

[k4t5UM0t0]

Did anyone label the y-axis or give the graph a title
and put the units on

I estimated it to 1260kJ/mol
b) incomplete combustion

 

[Fish Sauce]

lol I didn't even think about methanol I just whacked a straight line through those suckers.

I almost used 5 carbons etc. for my molecular weight, no idea what I was thinking. I got 2000 and something and it was off the graph. So glad I realised I was being the biggest dumbass ever and fixed my mistake.

 

[ravdawg]

lol I didn't even think about methanol I just whacked a straight line through those suckers.

I almost used 5 carbons etc. for my molecular weight, no idea what I was thinking. I got 2000 and something and it was off the graph. So glad I realised I was being the biggest dumbass ever and fixed my mistake.

lol i did the same thing, when i read its theoretical value should b more than 2000 i was like wtf it is... Oh shit, does anyonen have a rubber

 

[mitchbazza]

Did anyone label the y-axis or give the graph a title
and put the units on

I estimated it to 1260kJ/mol
b) incomplete combustion

Yeah i labelled and gave the graph a title.

and for b) alkanols contain oxygen atoms, they usually combust completely.. hence ethanol burns clear. I think i just went with impurities and possible dilution

 

[Forbidden.]

Yeah i labelled and gave the graph a title.

and for b) alkanols contain oxygen atoms, they usually combust completely.. hence ethanol burns clear. I think i just went with impurities and possible dilution

Oh god, damn there are so many ways to not gain full marks (rather than lose marks in the old HSC) other than not including a title.

 

[chocolate_lover]

I labelled the y-axis. I was going to give it a title (I remembered that I needed to give it a title) but I didn't know what to name it, so I just left it.

 

[Forbidden.]

I labelled the y-axis. I was going to give it a title (I remembered that I needed to give it a title) but I didn't know what to name it, so I just left it.

I labeled the y-axis too.

 

[mithril1337]

Silly question:

did you remember to plot the molecular weights according to the substances molecular weight and not a fixed point in the x-axis??

well i got 1360

 

[hecticleb]

yea thats true methanol is the smallest value thats where my line started and propanol was like 1320 right?

 

[Fish Sauce]

Silly question:

did you remember to plot the molecular weights according to the substances molecular weight and not a fixed point in the x-axis??

well i got 1360

What do you mean?

 

[ravdawg]

P.S if u wanna know how ur graph was meant tolook like check 03 q 25, and look at the alkanols line. I dont think they wouldve cut marks for not starting at meth, but u never know.

 

[mzduxx2006]

I plotted my molecular weight across the horizontal axis in 20 unit increments.
I plotted my molar eight of combustion across the vertical axis in 200 kJ/mol increments.
Unfortunately my line of best fit didn't even go through any of my plots (crosses)

My estimated heat of combustion for 1-propanol was 1700 kJ/mol ... I think that's way off ...
My reason why other than heat loss why the heat of combustion was less than the theoretical value was 'incomplete combustion may have occurred as a result of lower oxygen levels in the laboratory'.

omg yes i said incomplete combustion as well...HIGH FIVE!

my estimation however was around 1300 which was still way OFF bahahaha

 

[Forbidden.]

omg yes i said incomplete combustion as well...HIGH FIVE!

my estimation however was around 1300 which was still way OFF bahahaha

Ooohh HIGH 5 back for someone who agrees to a plausible reason ! :wave:

 

[Romina]

no one can be as WAY off as me, i got 2550 HAHAHAHAHAHA

failure here I come!

 

[mzduxx2006]

Was joining the dots what you meant by line of best fit? If not then yeiks.

I think I put down 1320 KJ /mol for 1 - propanol

omg i got near there aswell.....lulling myself into a false sense of security here peopleS!!!!

 

[Forbidden.]

no one can be as WAY off as me, i got 2550 HAHAHAHAHAHA

failure here I come!

I like the numerical madness.

Thanks to this Chemistry exam thoughts forum my rate of post counts increased dramatically .

 

[Steth0scope]

the graph can NOT go through the origin if the origin is zero...

and b is incomplete combustion

we did a whole assessment task worth 25% on this shit