Qualification > Sciences
ALL CIE CHEMISTRY DOUBTS HERE !!
HUSH1994:
how do u calculate the enthalpy change of combustion, and what do u use the values given at the data booklet for,i need help in:
C8H18 + 12.5 O2 ------- 8CO2 + 9 H2O
I need full detailed explanation please,i know the defenition but how to calculate it
elemis:
--- Quote from: ~~!$!HUSH!$!~~ on March 08, 2011, 03:38:40 am ---how do u calculate the enthalpy change of combustion, and what do u use the values given at the data booklet for,i need help in:
C8H18 + 12.5 O2 ------- 8CO2 + 9 H2O
I need full detailed explanation please,i know the defenition but how to calculate it
--- End quote ---
Calculate the energy needed to break the bonds of the reactants and subtract the energy needed to form the products.
Just use the bond dissociation energies given in the Data Booklet.
Deadly_king:
--- Quote from: TheLonelyIsland on March 07, 2011, 12:59:14 pm ---thx a lot, i knew it was something really easy... What confused me was that Mr H2=2... Dumb, I know! Thx, again!
--- End quote ---
Don't worry dear........it happens. You'll get used to it with time and more practice ;)
xlane:
i need explanation of partition coefficient and two immiscible layers...its for p5.......so i need the complete explanation.....some 1 help me out please....and does any1 know any p5 question based on this two topics ?
Amelia:
--- Quote from: xlane on March 08, 2011, 11:57:44 am ---i need explanation of partition coefficient and two immiscible layers...its for p5.......so i need the complete explanation.....some 1 help me out please....and does any1 know any p5 question based on this two topics ?
--- End quote ---
- The word 'partition' means a substance X is distributed between two phases in a dynamic equilibrium.
- It is a heterogeneous equilibrium since the 'solute' is distributed between two distinct phases.
- The two phases may be a gas and liquid-solution or, more likely, two immiscible liquids.
The basic expression is:
Kpartition = [X(phase 1)] / [X(phase 2)]
Here the K is called the partition coefficient or distribution coefficient. If it involves two immiscible liquids, K has no units.
The partition will involve the distribution of a solute between two immiscible liquid phases, which is a more likely and simpler situation to deal with.
If the solute is in the same molecular state in both liquid-phases, the following simple partition equilibrium expression will apply:
Kpartition =
[X(liquid 1)]
----------------
[X(liquid 2)]
K is called the partition/distribution coefficient and has no units and is temperature dependent.
Both concentrations must be in the same units e.g. molarity mol dm-3, g dm-3, mg cm-3 or whatever.
If a substance is added to a mixture which is soluble to a greater or lesser extent in both immiscible liquids, on shaking and then allowing the mixture to settle, the concentrations in each layer become constant. However, there is continual interchange of solute between the liquid layers via the interface i.e. a dynamic equilibrium is formed.
If more of the substance X is added to the system, the solute will distribute itself between the immiscible liquids so that the ratio of the solute concentrations remains the same at constant temperature independently of the total quantity of X in the same molecular state, and that is essentially the partition equilibrium law.
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