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2012/p2/qn 3a
what would be seen in the container after agcl is left 1 hr in daylight?
why ag+ will be reduced to ag(s) ? is it becos sunlight and oxygen oxidise cl- into cl2(g) , then ag+ become ag(s) ah??
shinglee's 2016 soln by mark ong state that "white ppt turned dark grey/black due to reduction of ag+ to ag "
from wiki, ag(s) is a "lustrous white metal"
from jc book and notes, i thought ag is silver(mirror) appearance? why would it be dark grey or black?
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page 292 cs toh advanced guide
would my translation be appropriate : "some strain in the ring" instead of "some puckering of the ring" by cs toh?
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page 292 cs toh.
eh actually, how would one determine if a molecule is planar or not?
in cyclobutane, all the C atoms are connected to 4 groups, electronic geometry is tetrahedral in the 1st place, how can it be (trigonal or square) planar?
is it to determine if a molecule is planar or not, all the atoms in the main chain in the molecule(example C, N, O) ,must all have same bond angles ah?
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Originally posted by Flying grenade:
2012/p2/qn 3a
what would be seen in the container after agcl is left 1 hr in daylight?
why ag+ will be reduced to ag(s) ? is it becos sunlight and oxygen oxidise cl- into cl2(g) , then ag+ become ag(s) ah??
shinglee's 2016 soln by mark ong state that "white ppt turned dark grey/black due to reduction of ag+ to ag "
from wiki, ag(s) is a "lustrous white metal"
from jc book and notes, i thought ag is silver(mirror) appearance? why would it be dark grey or black?
Warning for FlyingGrenade : do not spam too many qns at one shot, or I'll ignore all ur qns. Just post 1 at a time, wait patiently for up to 24 hours for me to reply ur 1st qn, then post ur next qn.Yes, UV light in sunlight provides the Ea for the redox reaction. When silver is exposed to air, it oxidizes into black silver(I) oxide.
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Originally posted by Flying grenade:
page 292 cs toh advanced guide
would my translation be appropriate : "some strain in the ring" instead of "some puckering of the ring" by cs toh?
No. Puckering (ie. 3 dimensional conformation) is a means by which the ring seeks to minimize ring strain due to angle strain. -
Originally posted by Flying grenade:
page 292 cs toh.
eh actually, how would one determine if a molecule is planar or not?
in cyclobutane, all the C atoms are connected to 4 groups, electronic geometry is tetrahedral in the 1st place, how can it be (trigonal or square) planar?
is it to determine if a molecule is planar or not, all the atoms in the main chain in the molecule(example C, N, O) ,must all have same bond angles ah?
CS Toh is referring to planarity (ie. whether or not the molecule is planar, but it isn't! even when) in regard to C atoms only. Cambridge will specify in regard to which atoms.Not necessarily all the same bond angles, but rather that each atom's molecular geometry must be planar (ie. linear or trigonal planar).
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https://www.dropbox.com/s/l9ndyy09c4e1qfj/Screenshot_2016-06-22-20-42-44-1.png?dl=0
so cyclobutane exists as conformers is it?
from the pic above by cyclo butane wiki page, how does the molecule looks like it's planar?
for both conformers, there seems to be a total of 4 planes that the molecule is oriented at
so the C atoms in cyclobutane force its own molecular geometry to be trigonal planar when its electronic geometry is tetrahedral?
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Originally posted by Flying grenade:
https://www.dropbox.com/s/l9ndyy09c4e1qfj/Screenshot_2016-06-22-20-42-44-1.png?dl=0
so cyclobutane exists as conformers is it?
from the pic above by cyclo butane wiki page, how does the molecule looks like it's planar?
for both conformers, there seems to be a total of 4 planes that the molecule is oriented at
so the C atoms in cyclobutane force its own molecular geometry to be trigonal planar when its electronic geometry is tetrahedral?
It's not planar. Wiki says it's not planar. CS Toh says it's not planar. Why do u keep obsessing about it being planar? No, the C atoms do NOT "force its own molecular geometry to be trigonal planar", because cyclobutane isn't planar. Enuff nonsense. Anything further on this, ask ur school teacher or private tutor. -
ooh sorry haha i read the sentence wrongly in cstoh's page
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" ion - permanent dipole interactions are stronger than hydrogen bonding, as long as the formal charge is on a small period 2 atom. "
hi ultima, may i ask, what is the comparison?
ion permanent dipole interactions between nh4+ and h2o molecules, and H bond between nh3 and h2o ah?
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when do we use miscible and soluble?
is NH3 miscible and/or soluble with/in water?
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Originally posted by Flying grenade:
" ion - permanent dipole interactions are stronger than hydrogen bonding, as long as the formal charge is on a small period 2 atom. "
hi ultima, may i ask, what is the comparison?
ion permanent dipole interactions between nh4+ and h2o molecules, and H bond between nh3 and h2o ah?
Best to compare phenoxide vs phenol (ie. addition of OH-), phenylammonium vs phenylamine (ie. addition of HCl), in terms of increased solubilities (as a consequence of ion - permanent dipole being stronger than H bonds, or alternatively, H bonds strengthened by formal charges).U prolly won't understand this fully, go ask ur school teacher or private tutor, instead of annoying me by flogging the dead horse as u are wont to do (ie. keep asking qns subsequently & repeatedly on the same topic, coz u dun understand my replies, that's damn annoying).
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Originally posted by Flying grenade:
when do we use miscible and soluble?
is NH3 miscible and/or soluble with/in water?
If a solute is miscible with a solvent, then the solute is considered to be soluble in that solvent. -
Originally posted by UltimaOnline:
If a solute is miscible with a solvent, then the solute is considered to be soluble in that solvent.swee, thx thx
miscible for liquids, soluble for solids
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Originally posted by UltimaOnline:
Best to compare phenoxide vs phenol (ie. addition of OH-), phenylammonium vs phenylamine (ie. addition of HCl), in terms of increased solubilities (as a consequence of ion - permanent dipole being stronger than H bonds, or alternatively, H bonds strengthened by formal charges).U prolly won't understand this fully, go ask ur school teacher or private tutor, instead of annoying me by flogging the dead horse as u are wont to do (ie. keep asking qns subsequently & repeatedly on the same topic, coz u dun understand my replies, that's damn annoying).
OOOOHH THANKS ULTIMA !!!!!
i understand this reply haha thanks
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Hi, for a level 2015 paper 2 question 3bi, i said to provide energy to overcome the actication energy of the reaction. Or should i say to provide the energy to for cl2 to homolytic fission? for 3biii, i said the homolytic fission of cl2 release free chlorine radicals which are very reactive, and they initiate a chain reaction with h2 gas.hence reaction becomes increasingly faster. for 4bii, cause ch3i is a primary iodoalkane, resulting in less steric hindrance around the c atom. It cannot undergo sn1 because of the because the carbocation intermediate produced is very unstable. are my answers acceptable?
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Originally posted by ArJoe:
Hi, for a level 2015 paper 2 question 3bi, i said to provide energy to overcome the actication energy of the reaction. Or should i say to provide the energy to for cl2 to homolytic fission?
for 3biii, i said the homolytic fission of cl2 release free chlorine radicals which are very reactive, and they initiate a chain reaction with h2 gas.hence reaction becomes increasingly faster.
for 4bii, cause ch3i is a primary iodoalkane, resulting in less steric hindrance around the c atom. It cannot undergo sn1 because of the because the carbocation intermediate produced is very unstable.
are my answers acceptable?
You should say both "activation energy" and "to homolytically cleave the Cl-Cl bond".Insufficient : you must specify that the propagation steps increase the molarity of the reactant free radicals, hence increasing the rate of reaction as predicted by the rate equation.
Yes, your answer is ok.
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"A chemical reaction is spontaneous if it is thermodynamically feasible, ie. Gibbs free energy change is negative."
from : http://sgforums.com/forums/2297/topics/488922
i thought that for a reaction to be spontaneous, must be both thermodynamic feasible and kinetically feasible?
backed up by this " Spontaneity implies both kinetic feasibility as well as thermodynamic feasibility. "
from : http://sgforums.com/forums/2297/topics/489346
e.g. diamond to graphite thermodynamically favourable/feasible, but kinetically not favourable/feasible
can't think of an example where a reaction is kinetically favourable, but not thermodynamically feasible
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wow, that thread regarding the discussion of energetics is awesome
another good learning point :important point that systems can be viewed in either isolation or coupled.
Examples of thermodynamically non-feasible or non-spontaneous reactions from H2 Biology that certainly continue to occur (otherwise you wouldn't be alive to read this), would be photosynthesis and protein synthesis.
woah yes, just recalled ,that a reaction with Positive change in gibbs free energy can still occur ! e.g. photosynthesis, which requires a continuous supply of energy from sunlight
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Originally posted by Flying grenade:
"A chemical reaction is spontaneous if it is thermodynamically feasible, ie. Gibbs free energy change is negative."
from : http://sgforums.com/forums/2297/topics/488922
i thought that for a reaction to be spontaneous, must be both thermodynamic feasible and kinetically feasible?
backed up by this " Spontaneity implies both kinetic feasibility as well as thermodynamic feasibility. "
from : http://sgforums.com/forums/2297/topics/489346
e.g. diamond to graphite thermodynamically favourable/feasible, but kinetically not favourable/feasible
can't think of an example where a reaction is kinetically favourable, but not thermodynamically feasible
Spontaneity can refer to either in regard to thermodynamics alone (after all, a reaction that is more thermodynamically feasible than it is kinetically feasible, can still 'spontaneously' happen after a million years), or thermodynamics together with kinetics, depending on the particular exam question. Be exam-smart, and deduce what Cambridge is asking and what Cambridge is testing you to write. -
Originally posted by UltimaOnline:
Spontaneity can refer to either in regard to thermodynamics alone (after all, a reaction that is more thermodynamically feasible than it is kinetically feasible, can still 'spontaneously' happen after a million years), or thermodynamics together with kinetics, depending on the particular exam question. Be exam-smart, and deduce what Cambridge is asking and what Cambridge is testing you to write.OOH YEA ! okay thanks !!! i just recalled !!
diamond is indeed undergoing formation to graphite, albeit reaction is so slow, it takes millions of years
thanks
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then is it right that all(thermodynamically feasible) chemical reactions are undergoing and happening , even if the reaction conditions are inadequate to provide the Ea required for the reaction to occur?
means that all the reactants are indeed forming the products even when Ea of reaction is not achieved (albeit over thousands/millions of years) , instead of remaining as reactants as it is?
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Originally posted by Flying grenade:
then is it right that all(thermodynamically feasible) chemical reactions are undergoing and happening , even if the reaction conditions are inadequate to provide the Ea required for the reaction to occur?
means that all the reactants are indeed forming the products even when Ea of reaction is not achieved (albeit over thousands/millions of years) , instead of remaining as reactants as it is?
Don't forget, all reactions are equilibrium reactions (it's a matter of where, and how far, the position of equilibrium lies, under what conditions, and conditions are changing all the time). What you call 'reactants' are actually products for the opposite reaction. And every species that exist in the Universe is part of a multiple web of different chemical reactions simultaneously. It's beautifully complex : infinite diversity in infinite creation.One more thing about your statement "even when Ea of reaction is not achieved", you've apparently forgotten the Maxwell-Boltzmann distribution : it's about the % of molecules with energy equals or exceeding Ea, not a binary 1 or 0, all or nothing. Even at low temperatures, a small % of molecules will have the required Ea for the reaction.
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OMG ULTIMA THANK UUU!!!!!!!!! superb !!! BJC Ftw