Question

2NaHCO(s) Na CO,(s) o,(8)+H,0(B) + 6. Sodium carbonate can be made by heating sodium bicarbonate: a. Calculate ? using the standard enthalpies of formation. b. Predict the sign of AS®. Calculate AS using the standard entropies. Are your re Calculate AS using the standard entropies. Are your results consistent with your prediction? Support your answer with a 1 sentence explanation. C. d. Calculate AGo using the standard free energies of formation Will the reaction be spontar e. At what temperatures will the reaction be spontaneous?

Answer 1

d. At 25 c the reaction is non spontaneous becuase free energy chenge is positive.

2 NaHCO_3 (s) rightarrow Na_2 CO_3 (s) + CO_2 (g) + H_2 O(g) a delta H^degree = [delta H^degree (Na_2 CO_3) + delta H^degree (CO_2) + delta H^degree (H_2 O)] - [2 delta H^degree (NaHCO_3)] = [-1130.94 KJ + (-393.51 KJ) + (-241.82 KJ)] - [2 times (-947.68 KJ)] = 129.09 KJ DoubleRightarrow Endothermic b delta S^degree = + ve DoubleRightarrow endothermic delta S^degree = [delta S^degree (Na_2 CO_3) + delta S^degree (CO_2) + delta S^degree (H_2 O)] - [2 delta S^degree (NaHCo_3)] delta S^degree = [135.98 J/K + 188.72 J/K 213.68 J/K] - [2 times 102.09 J/K] = 339.2 J/K downarrow + ve DoubleRightarrow means entropy increases c delta G^degree = delta H^degree - T delta S^degree = 129.09 times 10^3 J - 298 K times 334.2 J/K = 29.498 KJ (non spontaneous) d delta G^degree = [delta G^degree (Na_2 CO_3) + delta G^degree (CO_2) + delta G^degree (H_2 O)] - [2 delta G^degree (NaHCO_3)] = [-1047.67 - 334.38 - 228.59] - [2 times [-851.86] = 33.08 KJ (non spontaneous T = 25 degree C = 298 K K = 1.6 times 10^-6 delta G^degree = -RT ln K = -8.314 times 298 ln 1.6 times 10^-6 = 33.06 KJ (not favorable)