From the values of δh and δs, predict which of the following reactions would be spontaneous at 28°c: reaction a: δh = 10.5 kj/mol, δs = 30.0 j/k·mol; spontaneous nonspontaneous impossible to tell reaction b: δh = 1.8 kj/mol, δs = −113 j/k · mol, spontaneous nonspontaneous impossible to tell if either of the reactions is nonspontaneous, can it(they) become spontaneous? yes, reaction a can become spontaneous yes, reaction b can become spontaneous yes, both reactions can become spontaneous no, neither reaction can become spontaneous if either of the reactions is nonspontaneous but can become spontaneous, at what temperature might it become spontaneous? °c

Reaction A is nonspontaneous and it can become spontaneous above 77°C.

Reaction B is nonspontaneous and it cannot become spontaneous.

Explanation:

To determine if a reaction is spontaneous, we need to consider the Gibbs free energy (ΔG).

ΔG can be calculated using the following expression.

ΔG = ΔH - T.ΔS

where,

ΔH: enthalpy of reaction

T: absolute temperature

ΔS: entropy of reaction

From the values of ΔH and ΔS, predict which of the following reactions would be spontaneous at 28°C (301 K):

Reaction A: ΔH = 10.5 kJ/mol, ΔS = 30.0 J/K·mol;

ΔG = ΔH - T.ΔS = 10.5 × 10³ J/mol - 301K . 30.0 J/K.mol = 1470 J/mol

Since ΔG > 0, the reaction is nonspontaneous.

It can become spontaneous when ΔG < 0,

ΔH - T.ΔS < 0

ΔH < T.ΔS

T > ΔH / ΔS = (10.5 × 10³ J/mol)/(30.0 J/K.mol) = 350 K

The reaction will become spontaneous above 350 K (77 °C)

Reaction B: ΔH = 1.8 kJ/mol, ΔS = −113 J/K · mol

ΔG = ΔH - T.ΔS = 1.8 × 10³ J/mol - 301K . (-113 J/K.mol) = 3.58 × 10⁴ J/mol

Since ΔG > 0, the reaction is nonspontaneous.

Under no conditions can ΔG be negative, so the reaction cannot be spontaneous.