We’re being asked to determine which reactions is spontaneous at all temperatures.
Recall that when ΔH and ΔS are given, we can determine the spontaneity of the reaction based on their signs.
We can use the Punnett square shown below:
Which of the following reactions would you predict to be spontaneous at all temperatures (assuming ΔH°rxn does not change significantly with temperature)?
H2S(g) + 2 O2(g) → H2SO4(l) ΔH°rxn= –793 kJ/mol
2 Ag(s) + 3 N2(g) → 2 AgN3(s) ΔH°rxn = +1240 kJ/mol
C6H6(l) + 3 H2(g) → C6H12(l) ΔH°rxn = –207 kJ/mol
Na2CO3(s) + 2 HCl(aq) → 2 NaCl(aq) + H2O(l) + CO2(g) ΔH°rxn = –834 kJ/mol
CaCO3(s) → CaO(s) + O2(g) ΔH°rxn = +179 kJ/mol