Which of the following pairs of a chemicals reaction is certain to...

For spontaneous reaction $\Delta \mathrm{H}=-v e$, $\Delta \mathrm{S}=+v e$ Related Theory When the reaction is exothermic (negative $\triangle H$ ) but undergoes a decrease in entropy (negative $\Delta S)$, it is the enthalpy term which favours the reaction. In this case, a spontaneous reaction is dependent upon the TAS term being small relative to the $\Delta H$ term, so that $\triangle G$ is negative. The freezing of water is an example of this type of process. It is spontaneous only at a relatively low temperature. Above $273 \mathrm{~K}$, the larger $T \Delta S$ value causes the sign of $\triangle G$ to be positive, and freezing does not occur. Caution Students usually confuse the term spontaneous with the notion that a reaction occurs rapidly. A spontaneous reaction is one in which product formation is favoured, even if the reaction is extremely slow.