Question

calculate DH for the reactions...

1. KOH(s) + HCl(aq) -> KCl(aq) + H2O(l)

2.KOH(s) + HNO3(aq)   -> KNO3(aq) + H2O(l)

Answer 1

Enthalpy of a reaction or energy change of a reaction DH, is the amount of energy or heat absorbed in a reaction. If the energy is required, DH is positive, and if energy is released, the DH, is negative.

ENTHALPY OF REACTION

1. Case

[ΔHf(KCl (aq)) + ΔHf(H2O (l))] - [1ΔHf(HCl (aq)) + 1ΔHf(KOH (aq))]
[1(-419.55) + 1(-285.83)] - [1(-167.15) + 1(-482.39)] = -55.84 kJ
As -55.84 kJ hence reaction is (exothermic).

2. Case

[ΔHf(KNO3 (aq)) + ΔHf(H2O (l))] - [1ΔHf(HNO3 (aq)) + 1ΔHf(KOH (aq))]

[1(-494) + 1(-285.83)] - [ 1(-482.39) - 1(-207) ] = - 89.61

Hence reaction is exothermic