Question

Lab 16: Hess's Law Hess's Law 4. In accordance with Hess's Law, manipulate the following equations and their AHn's to calculate AHn for the reaction HCIO, + NH, NH CIO HCIOa)LiOHa) LiCIO4aH2Oo CH3COOHa+NH)NHCHcoOag) CHCOOHa+LiOH)LICH3CO0(a)+H2O AHpn= kJ/mol AHn kJ/mol AHpn kJ/mol НСО, +NHs NHCIO (ag) AHpn kJ/mol

Answer 1

Let $\Delta$H1 = x for the first reaction: HClO4(aq) + LiOH(aq) ----> LiClO4(aq) + H2O(l)

Let $\Delta$H2 = y for the second reaction: CH3COOH(aq) + NH3(aq) ----> NH4CH3COO(aq)

Let $\Delta$H3 = z for the third reaction, then the reverse of third reaction: LiCH3COO(aq) + H2O(l) ----> CH3COOH(aq) + LiOH(aq)

By adding the above three reactions, you will get the following equation.

HClO4(aq) + NH3(aq) + LiCH3COO(aq) ----> LiClO4(aq) + NH4CH3COO(aq)

i.e. HClO4(aq) + NH3(aq) + Li⁺(aq) + CH3COO^-(aq) -----> Li⁺(aq) + ClO4^-(aq) + NH4⁺(aq) + CH3COO^-(aq)

i.e. HClO4(aq) + NH3(aq) ----> NH4ClO4(aq)

According to Hess's law, the overall $\Delta$H for the above reaction can be calculated as follows.

$\Delta$H = $\Delta$H1 + $\Delta$H2 - $\Delta$H3 = x + y - z