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last SG · 2015-08-19T22:54:00+00:00

Topic : atomic radius Hi! This is from singapore cambridge nov a level exam year 2010,Paper 1 qn 1Qn: which element has the largest atomic radius?BrKKrScSo...

Flying grenade SG

tried very hard to google but yielded no pertinent/relevant findings

moved on alr, in the meantime,

anyone please feel free to answer my qn

why using cold water, results in partial/limited hydrolysis of PCl5 and SiCl4

additional, not so important qn : is there any link to exothermic rxn? if so, what's the link?

temp affects kinetics

partial hydrolysis of SiCl4 is an exothermic rxn

UltimaOnline SG

tried very hard to google but yielded no pertinent/relevant findings

moved on alr, in the meantime,

anyone please feel free to answer my qn

why using cold water, results in partial/limited hydrolysis of PCl5 and SiCl4

additional, not so important qn : is there any link to exothermic rxn? if so, what's the link?

temp affects kinetics

partial hydrolysis of SiCl4 is an exothermic rxn

You already answered your own question liao. Only when there is sufficient energy present to overcome the activation barrier on both sides (for any given reaction), then equilibrium comes into play. But bear in mind that position of equilibrium (ie. Qc vs Kc) is of course influenced by molarities of reactants vs products.

For reactions that can proceed at rtp, in limited water, write the partial hydrolysis equation ; in excess water, write the full hydrolysis equation. If not sure if water is limiting or excess, be BedokFunland JC exam-smart and write both (with qualification and/or explanation).

That's it liao, stop OCDing over this. I won't reply anymore on this. Go ask your school teacher or private tutor. Go waste their time, don't waste mine.

UltimaOnline SG

Biological reactions involve chiral enzymes acting on chiral substrates, hence only one enantiomer is the correct enantiomer to produce to correct effect. The other enantiomer can either be useless, or extremely toxic (eg. carcinogenic). This is an important consideration when manufacturing pharmaceutical medicinal drugs.

Flying grenade SG

OHHH OKAY THANK U SO MUCH ! alot of ur replies we dunno and didnt even thought about it

thanks for teaching us

Flying grenade SG

lol (non) innocent ligand

https://en.m.wikipedia.org/wiki/Non-innocent_ligand

Flying grenade SG

One of the reactants, A, for example, would have a significantly high concentration, while the other reactant, BB, would have a significantly low concentration

One way to create a pseudo-1st-order reaction is to manipulate the physical amounts of the reactants. For example, if one were to dump a liter of 5 M HCl into a 55 M ocean, the concentration of the mixture would be closer or equal to that of the ocean because there is so much water physically compared to the HCl and also because 55 M is relatively larger compared to 5 M.

this is for http://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Kinetics/Reaction_Rates/Second-Order_Reactions/Pseudo-1st-order_reactions

the rate is apparently independent of the reactant concentration. The rates of these zero-order reactions do not vary with increasing nor decreasing reactants concentrations. This means that the rate of the reaction is equal to the rate constant, kk, of that reaction. This property differs from both first-order reactions and second-order reactions.

http://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Kinetics/Reaction_Rates/Zero-Order_Reactions

Flying grenade SG

IJC 2016 P2

https://www.dropbox.com/s/kcwxb76pfu81oq2/20161004_194848.jpg?dl=0

from above, for zero order of rxn , the rate is apparently independent of the reactant concentration.

idk when use pseudo zero order or pseudo first order

ok for more common one, for water, is the order of rxn wrt H2O pseudo first or zero?

what abt other cases like the IJC one above, where the answer gave the order of rxn to be pseudo first

Flying grenade SG

it's really confusing , for pseudo zero and pseudo first

is it for pseudo first, the rate of reaction is still dependent on the reactant, albeit independent of concentration or partial pressure of the reactant

pseudo zero is independent of the reactant

then for water, sometimes pseudo first sometimes pseudo zero , quite confusing

Flying grenade SG

is it like for most cases,

when H2O is in large excess/concentration remains relatively same, order of rxn wrt [H2O] is pseudo zero

when an reactant is in large excess/concentration remains relatively same, order of rxn wrt [reactant] is pseudo first

UltimaOnline SG

For the IJC qn, to determine the order of reaction wrt NO2, you need to make Cl2 pseudo zero order, by having it in large excess. Then the data shows that the rate of reaction is directly proportional to (partial pressure of NO2)^2, hence rate of reaction is second order wrt NO2.

Consider the hydrolysis of ester. The reaction is actually 1st order wrt to H2O, and 1st order wrt to ester, hence overall order of reaction is 2nd order. If you have H2O in large excess, then H2O becomes pseudo-zero order, then overall order of reaction becomes pseudo 1st order. In which case you can use constant half-life (applicable only to overall 1st order or overall pseudo 1st order reactions) of ester to determine the value of k' (ie. ln2 / half-life), then from k' = k [H2O], you can obtain the value of k.

To see how to apply what I just said to an actual A level exam question, see my BedokFunland JC question (on my BedokFunland JC website) : Kinetics_calculate_rate_constant_k

If using PC, you can control-F to search for keywords such as "Kinetics_calculate_rate_constant_k"

PS. Why don't I just provide a direct link? Coz I want to encourage you guys to be familiar with navigating to my list of other BedokFunland JC H2 Chem questions on my website.

Flying grenade SG

All my teachers in my school taught Everyone Cl2 should be pseudo first order for that IJC qn.

their wrong right? (oxymoron)

UltimaOnline SG

All my teachers in my school taught Everyone Cl2 should be pseudo first order for that IJC qn.

their wrong right? (oxymoron)

Yeah, but the answer you copied down (ie. your corrections) from your teacher is fine.

Flying grenade SG

To see how to apply what I just said to an actual A level exam question, see my BedokFunland JC question (on my BedokFunland JC website) : Kinetics_calculate_rate_constant_k

If using PC, you can control-F to search for keywords such as "Kinetics_calculate_rate_constant_k"

PS. Why don't I just provide a direct link? Coz I want to encourage you guys to be familiar with navigating to my list of other BedokFunland JC H2 Chem questions on my website.

ok thanks for this reply. understood

Flying grenade SG

Yeah, but the answer you copied down (ie. your corrections) from your teacher is fine.

ok noted thanks.

but yeah they said its pseudo first order (which i didnt copy) which is wrong

Flying grenade SG

i feel damn ._.

Flying grenade SG

then we rarely encounter pseudo first?

overall pseudo first is fine

UltimaOnline SG

then we rarely encounter pseudo first?

overall pseudo first is fine

Only for overall.

Flying grenade SG

whats the implication/meaning of pseudo first?

is it for pseudo first, the rate of reaction is still dependent on the reactant, albeit independent of concentration or partial pressure of the reactant

how to make pseudo first? may it high in concentration such that it's in large excess too?

Flying grenade SG

Only for overall.

okay

Flying grenade SG

what about this?

this is for http://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Kinetics/Reaction_Rates/Second-Order_Reactions/Pseudo-1st-order_reactions

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