Q8.
(a) Amount of hexane = 
= 0.0233 mol
1
q = 4154 x 0.0233 ( = 96.6 – 96.8 kJ)
ecf = M1 x 4154
1
Ccal =
= 7.79 – 7.81 (kJ K−1)
ecf = M2/12.4
If no other marks awarded, allow one mark for 4154/12.4 = 335
1
(b) q = CcalΔT = 7.79 x 12.2 = 95.0 kJ
Ecf for (a) x 12.2
If candidate converted 12.4 into kelvin in (a), ignore conversion to kelvin in (b)
1
(amount of octane =
= 0.0175 mol)
heat change per mole =
= 5417 kJ mol−1
Allow 5420 kJ mol−1
Using the value given:
6.52 x 12.2 = 79.54(4)
79.54/0.0175 = 4545
1
(c) pressure not constant in bomb calorimeter
Allow enthalpy change requires constant pressure
1
(d) 100 × 0.2 = 1.64%
12.2
Allow 1.6%
Allow 2% if working shown
NOT 2.0%
1
use bigger mass of fuel (so ΔT greater)
Allow octane or hexane as the fuel
Allow more / greater volume of fuel
1
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