Chemistry study thread (1 Viewer)

[Loz_metalhead]

Ok this is a thread where we all together study for chem. I will start

What are the 3 types of intermolceular forces and explain them.

is combustion an exothermic reaction or endo?

I know the answers its just so we can all ask each other questions...yeh.

 

[RideTheLightnin]

Alright, let me find my notes.

Intermolecular forces -

1. Dipole Dipole interactions - Forces exist between polar covalent molecules, the positive pole of one molecule is attracted to the negative pole of others. Raises melting point of substances. eg HCl
2. Dispersion forces - Exists in molecules where there is an even sharing of electrons (non polar) such as chlorine, hydrogen. Dispersion focrces create temporary dipoles when the electrons are scattering around the nucleus
3. Hydrogen bond - The permanent dipole created at the hydrogen end of the moleule will strongly attract the negative dipole at the other end of the molecule which results in a higher then expected bpt and mpt.

Is combustion an exothermic or endothermic reaction?

:worried: i really dont know......

Someone else answer it

 

[Guernica]

Combustion is Exothermic...


right?

 

[YBK]

What makes water sooooo speciaLL !?

 

[YBK]

Combustion is Exothermic...


right?

think so...

exothermic = releases energy

?

 

[Casmira]

correct, exo = greek for out, thats how i find it easy to remember

 

[[Damo]]

Alright, let me find my notes.

Intermolecular forces -

1. Dipole Dipole interactions - Forces exist between polar covalent molecules, the positive pole of one molecule is attracted to the negative pole of others. Raises melting point of substances. eg HCl
2. Dispersion forces - Exists in molecules where there is an even sharing of electrons (non polar) such as chlorine, hydrogen. Dispersion focrces create temporary dipoles when the electrons are scattering around the nucleus
3. Hydrogen bond - The permanent dipole created at the hydrogen end of the moleule will strongly attract the negative dipole at the other end of the molecule which results in a higher then expected bpt and mpt.

Is combustion an exothermic or endothermic reaction?

:worried: i really dont know......

Someone else answer it

another type of Int.Mol. force is ion-dipole, when an ionic substance is dissolved in water, the ion-dipole forces (cations attracted to negative poles of water and anions attracted to positive poles of water) overcome the electrostatic attraction of the ions, hence dissolution occurs.

 

[physician]

think so...

exothermic = releases energy

?

yeh combustion is an exothermic reaction

exothermic = releases heat (heat is given off)

endothermic = absorbs heat (heat is absorbed)

for example the combustion of ethanol:

C₂H₅OH + 3O₂ --> 2CO₂ + 3H₂O + Heat

 

[YBK]

correct, exo = greek for out, thats how i find it easy to remember

yeah, i always think of something like that too....

exo sounds like out ..

 

[YBK]

Alright, dispersion forces and dipole-dipole forces may exist in conjunction...

water is polar and that makes it such a great solvent, seeing it has both positive ends and a negative end.

 

[Loz_metalhead]

oh I didnt expect any replies. Would anyone like to do it over msn? We could have a group chat. My exams are next week.

And with hydrogen bonding, it occurs between flurine, oxygen and nitrogen when they are bonded to hydrogen.

Combustion is an exothermic reaction.

This is my msn address:
metalhead_forever@hotmail.com

 

[YBK]

oh I didnt expect any replies. Would anyone like to do it over msn? We could have a group chat. My exams are next week.

And with hydrogen bonding, it occurs between flurine, oxygen and nitrogen when they are bonded to hydrogen.

Combustion is an exothermic reaction.

This is my msn address:
metalhead_forever@hotmail.com

Hydrogen bonding is a stronger from of dipole-dipole, but in essense, is the same thing.

 

[HamuTarou]

Alright, dispersion forces and dipole-dipole forces may exist in conjunction...

water is polar and that makes it such a great solvent, seeing it has both positive ends and a negative end.

polar can only mix with polar substances. similarly, non-polar can only mix with non-polar substances. that's why water and oil cant mix.

hope this help

 

[[Damo]]

polar can only mix with polar substances. similarly, non-polar can only mix with non-polar substances. that's why water and oil cant mix.

hope this help

however, sucrose is able to dissolve in water but cellulose is insoluble.

 

[mitsui]

polar substances dissolve in polar substances, "like dissolves like"

but i think it also depends on the difference in the strength of both substances?
like some ionic stuff aren't soluble becoz the ionic bonds r stronger
but Iodine are not soluble becoz the dispersion forces between I and I, are way too weaker than the hydrogen bonding of water.

(quoted from teacher).. but stil in doubt.. ~.~

 

[HamuTarou]

however, sucrose is able to dissolve in water but cellulose is insoluble.

cellulose is non-polar. however sucrose is polar or i think slightly polar which is enough to dissolve in water.

ask ur teacher, cus the shittest thing about chem is 'there ar exceptions' like my teacher said....

 

[HamuTarou]

but Iodine are not soluble becoz the dispersion forces between I and I, are way too weaker than the hydrogen bonding of water.

mitsui, i did an experiment in yr 10 of dissolving iodine. of course iodine is insouble in water @ rtp, but once u boil the water, it will dissolve!. at room temp, the molecules just collide and repel each other. the boiled water gives the i molecules enough energy to collide with the H2O and bond together. the energy required is the activation energy (covered in energy module)

if u add strach to the iodine solution, it turns blue and u can test whether vitamin C is present.

 

[mitsui]

wow.. so much detail
we neva managed to finish the energy in chemistry this yr..so not a clue! ~.~
but i think temperature change does affect the solubilities

 

[HamuTarou]

blah, chem test on coming tues, have to know all this. =.='

temperature, particle size (crushing the solvent rather than a big lump) and catalyst are some the of factors that speed up the reaction time. i think concentration plays a role but not sure.

 

[felixcthecat]

my chem exams next term! but i don't get the polarity stuf... ><'' is water polar? and do we actually need to remember those numbers..?