Question

Use standard free energies of formation to calculate ΔG at 25 C for each of the following reactions.

A) 2CH₄(g)→C₂H₆(g)+H₂(g)
B) 2NH₃(g)→N₂H₄(g)+H₂(g)

Answer 1

To calculate ΔG° at 25°C, one must subtract the sum of standard free energies of formation of reactants from that of the products, using ΔG° = Σ ΔG°f(products) - Σ ΔG°f(reactants).

Step-by-step explanation:

To calculate the standard free-energy change (ΔG°) for a chemical reaction at 25°C using standard free energies of formation, we apply the equation ΔG° = Σ ΔG°f(products) - Σ ΔG°f(reactants), where ΔG°f represents the standard free energy of formation of a given substance.

The value of ΔG° helps us determine whether a reaction is spontaneous or nonspontaneous under standard conditions. To calculate ΔG°, we would look up the ΔG°f values for each species involved in the reaction from a data source such as an appendix or database.

Then perform the subtraction as indicated in the equation above. If the calculated ΔG° is negative, the reaction is spontaneous; if positive, it is nonspontaneous at 25°C.