Chemistry - Edexcel Unit 1 "The Core Principles of Chemistry" ~ January 2015

hello guys! I'm revising for my mocks right now, i'm completely lost with all these free radical mechanisms, if anyone knows a good site that can explain it, please help

is there any thread for AS biology as well? I'm appearing it in jan 2015 as well but can't find any thread for it so if you guys could help. TIA.

https://www.youtube.com/watch?v=5HgzsltWwK8
This is sooo helpful

Hey guys. Can anyone help me with multiple question of may 2014 unit 1 number 8, jan 2014 number 11 + 14? Exam is so near and can't find a solution for it. please help! TIA.

for may 2014 question 8 you have to find the number of moles of CO2 and H2O
so 1st step : find mole ratio of co2 to h2o which is (co2:88/44 = 2) and (h2o :27/18=1.5)

2nd step : write the chemical equation Ncxhy + O2 = 2Co2 + 1.5 H2o (where N stands for an unknown number ) notice i didnt balance o2 because it wont affect the answer

3rd step: divide the mass of unknown hydrocarbon (27 g ) by the molar mass of each choice for example for choice A (which is not the answer) you divide 27/(12+4) you will get a 1.6875 if you place that in the equation it won't balance the number of carbons and hydrogens (1.6875 CH4 + o2 = 2co2 + 1.5 h20).
However for example if you take choice C and divide 27 by c4h6 molar mass you will get 0.5 moles which would balance the number of carbons and hydrogens :
0.5 C4h6 + o2 = 2co2 + 1.5 h2o


Now for January 2014
question 11
first find the volume of products
20% of the 500cm3 which is (0.5 dm3) is 100cm3 which is (0.1 dm3) so find the number of moles of nh3 and using ration and proportion find the moles of moth n2 and h2 then multipy by 24 for each gas you will get for n2+h2 (200+400 cm3) then add the volume of the undecomposed nh3 which is (400 cm3) you will get an answer of 600 cm3

question 14

CO + 0.5 O=O -> O=C=O

for the Left hand side the total enthalpy required to break the bonds is
(1077 + (0.5 X 498 )

for the right hand side
805 X2 (as there are two c=o bonds in co2)

now subtract LHS from RHS you will get -248 which is choice A

Oh wow, you're a life saver!! Thanks a bunch!!

anyone have any good resources for hess diagrams/born haber? Can't seem to understand it and its been ages since i learnt it properly. Thanks!

When 0.1 mol of atoms of an element react with chlorine there's an increase in mass by 7.1 the g the element could be
A.carbon
B.sodium
C.magnesium
D.aluminum

The answer is C but whyyy please someone explain

Because when MgCl2 is formed, 2 chlorine atom is added to the Mg atom. This has a mass of 71g. As the mole the Mg is 0.1, mass of the compound is increased by 71/0.1 g.
I hope this helps.

Does anyone have a clear definition for first ionization energy? All the mark schemes seem to be different

Is the energy required to remove one mole of an electron from one mole of gaseous atom.
X(g)----> X+(g) + 1 electron.

thank you!