Heat of Combustion (1 Viewer)

[angelxtearz]

Hi,

I was just wondering what was being tested. On the sheet my teacher gave, it sed methanol, 2propanol, butanol and ethanol. However, according to Jamesy science website, he used 1 propanol n 2 propanol and methanol, ethanol and in my school txtbuk 'Spotlite' they had dffernet reagents, so which am i suppose dto take????

 

[Dreamerish*~]

It varies from source to source. The aim is to compare the molar heat of combustion of different alkanols and relate this to their physical properties (carbon-chain length, boiling point, etc). It doesn't matter which, or how many alkanols you use, as long as you are able to make a valid conclusion on the relationship between molecule size and energy per mole.

 

[angelxtearz]

hmm i dun reli get the bit about molecule size, i get the bit about chain length coz propanol, methanol and ethanol are all from the same functional group. only differing by the chain length.

 

[pLuvia]

This is an experiment you should have conducted in class, as Dreamerish*~ said the aim is to find out the heat of combustion of methanol, ethanol etc.

Molecule size is how big it would be, I assume methanol would be the smalled out of the listed ones you have. You should consult with your teacher with this one, because we were given it as a major assessment worth 15% of our internal marks

 

[insert-username]

The only thing we know about what's being tested is that it'll most likely be from C₁ to C₈. If you learn the IUPAC stems for the first 8 hydrocarbons (meth-, eth-, pro- but-, etc.), and remember that bigger molecule (i.e. the little numbers add up to more) = higher heat of combustion, you'll be set for any combination of alkanols, providing you can calculate heats of combustion.


I_F

 

[angelxtearz]

O so Ud never get isomers eg 1propanol 2 propanol, im juz askin cuz in jamesy science website, theres menshun o it

n also, i kno tht the greater molecule size means greater boiling pt...n so forth. y iz diz so?

cud sum1 plz explain
thankyooz

 

[Riviet]

n also, i kno tht the greater molecule size means greater boiling pt...n so forth. y iz diz so?

Basically, if you have a larger molecule, you'll have more elements bonded, hence it's harder to break all the bonds. Anyone else feel free to add.

 

[insert-username]

O so Ud never get isomers eg 1propanol 2 propanol, im juz askin cuz in jamesy science website, theres menshun o it

1-propanol and 2-propanol have exactly the same heat of combustion - they are still propanol. So you don't need to worry about different isomers - the only thing the number changes is the place of the OH group.


I_F

 

[pLuvia]

n also, i kno tht the greater molecule size means greater boiling pt...n so forth. y iz diz so?

Yes as Riviet said, the larger the molecule size the more bonds it will have which will require more energy to break those bonds. Also depending on which type of bonds it has, i.e. polar, non-polar or hydrogen bond, that will also affect the energy required to break the intermolecular forces in between each atom

 

[wanton-wonton]

Basically, if you have a larger molecule, you'll have more elements bonded, hence it's harder to break all the bonds. Anyone else feel free to add.

I dont think that's a good enough response.

A larger molecule has greater molecular weight which leads to greater dispersion forces and so more heat is required to break the forces. Hence, higher boiling point.

 

[Dreamerish*~]

Basically, if you have a larger molecule, you'll have more elements bonded, hence it's harder to break all the bonds. Anyone else feel free to add.

Wanton's right. Rivvy, you're talking about intramolecular forces, which does not affect the boiling point of a compound. What does affect it are the intermolecular forces, such as dispersion, dipole-dipole and hydrogen bonding.

 

[mitsui]

Wanton's right. Rivvy, you're talking about intramolecular forces, which does not affect the boiling point of a compound. What does affect it are the intermolecular forces, such as dispersion, dipole-dipole and hydrogen bonding.

can someone remind me wat dipole-dipole is again??
is it polar bonds? or is polar bonds intramolecular??

 

[NightShadow]

with dipole dipole its where a molecule say for instance H20, the oxygen in the molecule is highly electronegetive - ie it wants electrons pronto!
and since it has such an attraction for electrons in the covalent bondings between intramolecular bonded hydrogen and oxygen, the electrons spend a larger amount of time orbiting the oxygen ion,
THus that side of the water molecule is more negetive and hte hydrogen more positive. Thus hydrogen bonding occurs due to this "induced" disparity of charge, [hydrogen bonding is a stronger form of dipoledipole, so using a hypoerbolic example can illustrate it a bit better i reckon]

BTW .. hydrogen bonding is a type of dipole dipole rite?

well hydrogen bonding happens with Nitrogen, Oxygen or Fluorine and 10 times stronger than dipoledipole but its still counted as a dipoledipole interaction

 

[mitsui]

ok.
hydrogen bonding is type of dipole dipole, yes. =P

me taking a guess:

polar bonds - the bonds within a molecule such as H-Cl, where there is a diff in electronegativity

if there r polar bonds in a molecule, it has dipole attractions, and forms dipole dipole wif another such molecule

?? -"-"'

 

[Riviet]

well hydrogen bonding happens with Nitrogen, Oxygen or Fluorine

Just remember that Chemistry is FON!!

 

[Mountain.Dew]

ok.
hydrogen bonding is type of dipole dipole, yes. =P

me taking a guess:

polar bonds - the bonds within a molecule such as H-Cl, where there is a diff in electronegativity

if there r polar bonds in a molecule, it has dipole attractions, and forms dipole dipole wif another such molecule

?? -"-"'

*thumbs up*

 

[angelxtearz]

Wanton's right. Rivvy, you're talking about intramolecular forces, which does not affect the boiling point of a compound. What does affect it are the intermolecular forces, such as dispersion, dipole-dipole and hydrogen bonding.

but would the intermolecular forces be consistent through all the compounds eg. meth, eth, and propanol?

 

[Mountain.Dew]

but would the intermolecular forces be consistent through all the compounds eg. meth, eth, and propanol?

of course. when talking about these alkanols, we rarely talk about intramolecular forces.

remember this:

intramolecular forces is the 'forces' that bond the ELEMENT, the actual single individual ATOMS together to make ONE MOLECULE. E.G. NaCl has IONIC BONDING, Oxygen gas (O₂) has COVALENT BONDING.

intermolecular forces are the forces that bond those MOLECULES together --> things like polar bonds, dispersion forces, etc...

 

[angelxtearz]

ook.. higher molecular size = more intermolecular to break---> more energy required to do so?

 

[Mountain.Dew]

ook.. higher molecular size = more intermolecular to break---> more energy required to do so?

mmmmmmmm yes, but one important thing u missed out.

higher molecular size --> longer carbon chain --> more dispersion forces --> more energy to break the intermolecular bonds.

ie --> longer the chain, higher the boiling pt.