Question

For a given reaction, ΔH = +35.5 kJ/mol and ΔS = +83.6 J/Kmol. The reaction is spontaneous ________. Assume that ΔH and ΔS do not vary with temperature.
a) at T > 298 K
b) at T > 425 K
c) at all temperatures
d) at T < 425 K

Answer 1

Answer:

b) at T > 425 K

Explanation:

• ΔG = ΔH - TΔS

∴ ΔG < 0 ⇒ The reaction is spontaneous

∴ ΔG > 0 ⇒ The reaction is not spontaneous

∴ ΔG = 0 ⇒ The equilibrium

∴ ΔH = +35.5 KJ/mol

∴ ΔS = (+83.6 J/K.mol)*(KJ/1000 J) = 0.0836 KJ/K.mol

at T = 298 K:

⇒ ΔG = 35.5 KJ/mol

⇒ ΔG = 35.5 - (298)(0.0836) = 35.5 - 24.913 = 10.587 KJ/mol > 0... No spontaneous

at T = 425 K:

⇒ ΔG = 35.5 - (425)(0.0836) = 35.5 - 35.53 = - 0.03 KJ/mol < 0,,,,is spontaneous