help please quick!

can someone please explain these questions all from aqa june 03 6a synoptic

a)why does ch3chooch3(l) have no hydrogen bonding when pure?


b)Fe2O3+3h2 -> 2Fe(s) +3H2O (g)

deltaH=+96kJmol-1

Fe2O3 (s) deltaHf -8.22

standard enthalpy of formation of steam is -242kJmol-1

HOW?

similar thing for same reaction

deltaS=+138

Fe2o3 delta S = 90, h2=131, fe=27

entropy for steam should be +189 ?? how ??

c) butan-1-ol was converted into butyl propanoate by reaction with an excess of propanoic acid, in the reaction 6.0g of the alcohol gave 7.4g of the ester. % yield is...

(answer 70 don't know why)

thanks

can someone please explain these questions all from aqa june 03 6a synoptic

a)why does ch3chooch3(l) have no hydrogen bonding when pure?


b)Fe2O3+3h2 -> 2Fe(s) +3H2O (g)

deltaH=+96kJmol-1

Fe2O3 (s) deltaHf -8.22

standard enthalpy of formation of steam is -242kJmol-1

HOW?

similar thing for same reaction

deltaS=+138

Fe2o3 delta S = 90, h2=131, fe=27

entropy for steam should be +189 ?? how ??

c) butan-1-ol was converted into butyl propanoate by reaction with an excess of propanoic acid, in the reaction 6.0g of the alcohol gave 7.4g of the ester. % yield is...

(answer 70 don't know why)

thanks

a) H-bonding requires a H bonded covalantly to a strongly electronegative atom eg O, F, N. There isn't one on the methyl ethanoate molecule so by definition no H-bonds can occur

b)Something to do with latent heat of vapourisation I think - lot of energy has to be chucked at the waterto break the attractions between it (v strong H-bonds) so drawing out the cycle will only give the bond enthalpies.

c) Yield is observed moles over expected moles x 100%

Observed moles of the ester....

Mass = 130gmol^-1
Moles therefore = 7.4/130 = 0.0567...ish

Expected moles of ester = moles of the alcohol (1:1 reaction ratio, expect full reaction with excess carboxylic acid...
Mass = 74gmol^-1
Moles therefore = 6/74 = 0.0810..ish

observed/expected * 100 = 70%ish

thanks im sure thats right but there isnt time to draw any diagrams out, its a multiple choice q you are meant to spend less than 2mins on so what is the quick way? also where did that 130gmol come from?

can someone please explain these questions all from aqa june 03 6a synoptic

a)why does ch3chooch3(l) have no hydrogen bonding when pure?


b)Fe2O3+3h2 -> 2Fe(s) +3H2O (g)

deltaH=+96kJmol-1

Fe2O3 (s) deltaHf -8.22

standard enthalpy of formation of steam is -242kJmol-1

HOW?

similar thing for same reaction

deltaS=+138

Fe2o3 delta S = 90, h2=131, fe=27

entropy for steam should be +189 ?? how ??

c) butan-1-ol was converted into butyl propanoate by reaction with an excess of propanoic acid, in the reaction 6.0g of the alcohol gave 7.4g of the ester. % yield is...

(answer 70 don't know why)

thanks

OK, your first problem is simply a misprint! The standard enthalpy of formation of iron oxide must be -822 kJmol-1

therefore moving from the left hand side to the right hand side....

the Fe2O3 must be changed to elements (= negative delta Hf) = +822

energy change when steam is formed = delta Hf H2O(g) = -242 kJmol-1

But three moles of steam are formed = -726 kJ

therefore negative (sum) delta H reactants + (sum) delta H products = +92