NH_4NO_3(s) rightarrow NH_4^+ (aq) + NO_3^- (aq) Assuming that the values of Del
ID: 490846 • Letter: N
Question
NH_4NO_3(s) rightarrow NH_4^+ (aq) + NO_3^- (aq) Assuming that the values of Delta H degree and Delta S degree do not change appreciably with temperature, calculate the Delta G degree value for the reaction from the polyatomic ion data in standard thermodynamic property tables, and predict the lowest temperature at which the reaction is spontaneous. Delta G degree: T: Using Delta_rxn degree = Delta H_rxn degree - T Delta S_rxn degree can be determined from the standard thermodynamic tables using: Delta H_rxn degree = sigma n_products Delta H_f, products degree - sigma n_reactants Delta H_f, reactants degreeExplanation / Answer
The thermodynamic data for the compounds is
compound delta G(kJ/mol) delta H (kJ/mol) delta SJ/kmol
NH4NO3(s) -183.87 -365.56 151.08
NH4+ (aq) -79.31 -132.51 113.4
NO3-(aq) -108.74 -205.0 146.4
Thus delta G reaction = [-108.74-79.31] -[-183.87]
= -4.18 kJ
Delta H of raction =[-205.0 -132.51] -[-365.56]
= 28.05kJ
delta S pf reaction = [146.4+113.4] -151.08
=108.72 J
Thus the minimum temperature to obtain equilibrium is
T = delta H /delta S
=28.05x1000J / 108.72 J
= 258.00 K
since delta h is positive , above258K the reaction is spontaneous.
Thu the miniumum temperature above which the rection becomes spontaneous is 258K = -15 C
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