Answer to Question #204337 in General Chemistry for Nadia

Question

The standard enthalpies of formation of ions in aqueous solutions are obtained by arbitrarily assigning a value of zero to H+ ions; that is, ∆H°f [H+(aq)]=0.

a) For the following reaction

H2O

 HCl(g)

Calculate the ∆H°f for the Cl- iron.

H+(aq) + Cl- ∆H°=-74.9 kJ/mol

 

b) Given that ∆H°f for OH- ions is -229 kJ/mol, calculate the enthalpy of neutralization when 1 mole of a strong monoprotic acid (such as HCl) is titrated by 1 mol of a strong base (such as KOH) at 25°C.

Answer 1

H°_f (H⁺ _(aq)) + ∆H°_f (Cl _(aq)) - ∆H°_f (HCl _(g)) = ∆H°_rxn

1(0 kJ/mol) + ∆H°_f (Cl^- _(aq) - 1(-92.3 kJ/mol) = -74.9 kJ/mol

92.3 kJ/mol + ∆H°_f (Cl^- _(aq)) = 74.9 kJ/mol

= ∆H°_f (Cl^- _(aq)) = -167 kJ/mol