Question

chem:1220

ΔS is positive for the reaction ________.

A) 2NO (g) + O2 (g) → 2NO2 (g)

B) 2N2 (g) + 3H2 (g) → 2NH3 (g)

C) C3H8 (g) + 5 O2 (g) → 3CO2 (g) + 4 H2O (g)

D) Mg (s) + Cl2 (g) → MgCl2 (s) E) C2H4 (g) + H2 (g) → C2H6 (g)

Answer 1

Lets calculate for all

A)

S⁰ NO_2(g) = 239.7 J/mol K

S⁰ NO_(g) = 210.5 J/mol K

S⁰ O_2(s) = 205 J/mol K

S⁰ = S⁰ (Product) - S⁰ (Reactant)

S⁰ = [2 x ( S⁰ NO_2(g)) ] - [(2 x S⁰ NO_(g)) + (S⁰ O_2(g))]

= [ 2 x (239.7 ) ] - [(2 x (210.5 ))+  (205)]

= -146.6

S⁰ = -146.6 J/mol.K

Now same for all

B)

S⁰ = [2 x ( S⁰ NH_3(g)) ] - [(2 x S⁰ N_2(g)) + 3 x (S⁰ H_2(g))]

= [ 2 x 192.5] - [ 2 x 191.6 + 3 x 130.5 ]

= -389.7 J/mol.K

C)

S⁰ = [3 x ( S⁰ CO_2(g)) + 4 x S⁰ H₂O_(g))] - [(S⁰ C₃H_8(g)) + 5 x (S⁰ O_2(g))]

= [ 3 x 213.8 + 4 x 188.7 ] - [ 269.9 + 5 x 205]

= 101.3 J/mol.K

So your Answer is C)