Manipulate the following equations and their delta H In accordance with Hess\'s

Question

Manipulate the following equations and their delta H In accordance with Hess's Law, manipulate the following equations and their delta H_ s to calculate delta H_rxn for the reaction HClO_4 + NH_3 rightarrow NH_4ClO_4 ClO_4_4. HClO_4(aq) + Li OH rightarrow_(aq) + H_2O_(4) CH_3COOH_(aq) NH_3(aq) rightarrow CH_3COOH_(aq) CH_3COOH_(aq) + LiOH_(aq) rightarrow LiCH_3COO_(aq) + H_2O_(t) delta H_rxn = ___ kJ/mol delta H_rxn = ___ kJ/mol delta H_rxn = ___kJ/mol HClO_4(aq) + NH_3(aq) rightarrow NH_4ClO_4(aq) delta H_rxn = ___ kJ/mol

Explanation / Answer

(A) HClO4(aq) & LiOH(aq) --> Li+1 & (ClO4)-1 & H20 (l)
(B) CH3COOH (aq) & NH3(aq) --> (NH4)+1 & (CH3COO)-1
(C) CH3COOH(aq) & LiOH(aq) ---> Li+1 & (CH3COO)-1 & H20(l)

your equation:
HClO4 + NH3 ---> NH4)+1 & (ClO4)-1
uses equation (A) to provide HClO4
uses equation (B) to provide NH3
& subtracts equation (C) to cancel out LiOH , H2O, Li+1 & H3COO-1

notice that
C's Li+1 --> cancels out --> A's Li+1

leaving you with
HClO4 + NH3 ---> NH4)+1 & (ClO4)-1
i.e.
HClO4 + NH3 ---> NH4ClO4 (aq)

so by Hess's law, if A + B - C gives the equation that you wish
then
dH A + dHB - dHC = the energy you wish
56.8 kJ/mol & 45.6 kJ/mol - 58.8 kJ/mol = 43.6 kJ/mol

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