3-A

amount of energy required to break bondsof reactants

3 ×413 + 358 + 464 + 1.5 × 498 (kJ mol–1) / 2808 (kJ mol–1);

amountof energy released during bond formation of products
4 ×464 + 2 × 746 (kJ mol–1) /3348 (kJ mol–1);

 ∆H = –540 (kJ mol–1); 
Award[3] forcorrect final answer.
Award [2] for(+)540.

q= mc (delta T): m is always mass

3-C

(i)  bondenthalpies are average values/differ (slightly) from one compound to another (depending on the neighbouring atoms) / methanol is liquid not gas in the reaction

(ii)  not all heat produced transferred to water /heat lost to surroundings/environment / incomplete combustion (of methanol) / water forms as H2O(l) instead of H2O(g) 

4-C-ii (I give you a multiple possible answers)

(ii)theanhydrous copper(II) sulfate had already absorbed some water from the air / OWTTE;
the value would be less exothermic/less negative than expected as the temperature increase would be lower /
less heat will be evolved when the anhydrous salt is dissolved in water