At what temperatures, will a reaction be spontaneous if delta H degree = +45 kJ

Question

At what temperatures, will a reaction be spontaneous if delta H degree = +45 kJ and delta S degree = +312 J/K? The reaction will never be spontaneous. All temperatures above 144 K. Temperatures between 45 K and 312 K. The reaction will be spontaneous at any temperature. All temperatures below 144 K. The standard free energy change for a chemical reaction is +21.9 kJ/mol. What is the equilibrium constant for the reaction at 87 degree C? (R = 8.314 J/K mol 1.5 times 10^3 7.1 times 10^34 6.6 times 10^4 1.0 9.9 times 10^-1 The balanced chemical reaction represented by Pt | H_2(g) | h degree (aq) | SO_4^2- (aq) | PbSO_4 (s) | pb(a) is: PbSO_4 (s) + H_2 (g) rightarrow Pb(s) + 2 H^+ (aq) + SO_4^2- (aq) Pb^2+ (s) + H_2 (g) rightarrow Pb(s) + 2 H^+ (aq) Pb(s) + 2 H^+ (aq) rightarrow Pb^2+ (s) + 2 H_2 (g) Pb(s) + 2 H^+ (aq) + SO_4^2- (aq) rightarrow PbSO_4 (s) + H_2 (g) PbSO_4 (s) + 2 H^+ (aq) rightarrow Pb(s) + H_2 (g) + SO_4^2- (aq) Use the standard reduction potentials below to determine which element or ion is the best oxidizing agent. Hgr^2+ (aq) + 2 e rightarrow 2 Hg(t) E degree = +0.789 V I_2(s) + 2 e rightarrow 2 F(aq) E degree = +0.535 V Ni^2+ (aq) + 2 e rightarrow Ni(s) E degree = -0.25 V I_2 Hg(t) Hgt^2+ (aq) 1 (aq) Ni^2+ (aq)

Explanation / Answer

1) The equilibrium temperature is given by

T = delta H /delta S

= 45x1000J /312 J

= 144 K

Thus the reaction is spontaneous at all temperatures above 144 K (since endothermic)

Thus option B is correct.

b)We know the relation between free ennergy and equilibrium constant as

delta Go  = -2.303 RT log K

substituting delta G = 21.9x1000J , R = 8.314 J , T = 360 K ,

We get K= 6.7x 10-4

Thus the option C is correct.

c) The option A .

H2 + PbSO4 (s) -------> Pb(s) + 2H+(aq) + SO4-2(aq)

d) Since Hg has the most positive SRP value Hg+2 ion readily takes two electrons to get itself reduced to Hg. Thus Hg+2 is the best oxidising agent of the given species.

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