1) What is the sign of ΔH_rxn for a reaction in which the bonds are stronger in the products than in the reactants. Justify

2) A reaction is only spontaneous at high temperature. Predict and justify the sign of ΔH_rxn for this reaction

Question

1) What is the sign of ΔH_rxn for a reaction in which the bonds are stronger in the products than in the reactants. Justify

2) A reaction is only spontaneous at high temperature. Predict and justify the sign of ΔH_rxn for this reaction

| General Chemistry 3

Accepted Answer

1) ΔH_rxn = Σ H_bonds(reactants) - Σ H_bonds(products)

If Σ H_bonds(products) > Σ H_bonds(reactants), ΔH_rxn < 0

2) The reaction is spontaneous when ΔG_rxn < 0

ΔG_rxn = ΔH_rxn - TΔS_rxn

If a reaction is only spontaneous at high temperature ⇒ at low temperature ΔG_rxn > 0

At low temperature: ΔH_rxn >> TΔS_rxn ⇒ ΔG_rxn ≈ ΔH_rxn> 0

Midterm 2 - Question 2 | General Chemistry 3