Question

Data is for P 1 bar and 25C AH (kJ mol) NAg) H,(g) NH (g) S (J K mol ) 191.5 130.6 192.3 46.1 13) 812. (a) Calculate &G" for the tollawing reaction at 25 C. Ng) 3 H,(g) 2 NH,1g) (b) Account for the sign of &s. Give your reasoning Calculate the value of K-or the reaction at 3000'C. assumptions required 13] (c) State any 12) id) Calculate 4at 30 0 Cwhen PIN)- 300 bar P)1200 bar and P(NH,1-0.0010 bar (e) is the reaction to form NH, spontaneous under these conditione? Explain briofly

Answer 1

Answer – We are given standard enthalpy and entropy of each in given reaction and need to calculate the standard free energy for the reaction at temperature 25^oC –

N₂(g) + 3 H₂(g) <-----> 2 NH₃(g)

ΔH^o_rxn= ∑ ΔH^o_f of product – ∑ ΔH^o_f of reactant

= [ 2* ΔH^o_f NH₃(g)] – [ΔH^o_f N₂(g) + 3*ΔH^o_f H₂(g)]

= (2*46.1) – ( 0.00 + 3*0.00)

= 92.2 kJ/mol

ΔS^o_rxn= ∑ ΔS^o_f of product – ∑ ΔS^o_f of reactant

= [ 2* ΔS^o_f NH₃(g)] – [ΔS^o_f N₂(g) + 3*ΔS^o_f H₂(g)]

= (2*192.3) – ( 191.5 + 3*130.6)

= -200.7 J/mol.K

we know formula for standard free energy

ΔG^o_rxn= ΔH^o_rxn -T ΔS^o_rxn

            = 92.2 kJ/mol – 298K * (-0.2007 kJ/mol.K)

             = 152.0 kJ/mol