Heat of combustion and whatevv (1 Viewer)

[Bricktop]

Harro, can anyone tell me what units you get for heat of combustion if you use kgs for M? More importantly I guess, is what value for C you're meant to substitute if you're using kgs for M (ie 4.18 as opposed to 4.18 x 10^3)?

Probably simple but hey, I'm not great at Chem.

Cheers bruddas an sistahs.

 

[rama_v]

Harro, can anyone tell me what units you get for heat of combustion if you use kgs for M? More importantly I guess, is what value for C you're meant to substitute if you're using kgs for M (ie 4.18 as opposed to 4.18 x 10^3)?

Probably simple but hey, I'm not great at Chem.

Cheers bruddas an sistahs.

Do it mathematically:
H = -mc dT and if you are using c in units if J K^-1 kg^-1 then if you have m in kg, the kg's cancel out, and the dT is measured in K so that also cancels out, leaving only Joules.

 

[Nodice]

Well, in the markers notes for 2001 they commented on this issue. It doesnt really matter a whole lot, but they just noticed that a lot of people decided not to use the data sheet value for specific heat capacity of water, ie 4.18x10^3 Jkg-1K-1 instead using 4.18 Jg-1K-1
This basically means that if you just use 4.18, use your mass in grams. If you use 4.18x10^3 use the mass in kilograms.
Either way, its fine. The most 'correct' for the markers would be 4.18x10^3 but hey, as I said it doesnt matter.

 

[rama_v]

Constants are given in SI units. The base SI unit of mass is kg, surprisingly (not grams). So thats why they give it to you in kg.

 

[Bricktop]

Aaaah okay sweet Makes sense haha.

Thanks fellas!