Consider the dissociation reaction A₂(g) ⇌ 2 A(g). ...

Question

Consider the dissociation reaction A₂(g) ⇌ 2 A(g). The following pictures represent two possible initial states and the equilibrium state of the system:

(b) What are the signs ( + , - , or 0) of ∆H, ∆S, and ∆G when the system goes from initial state 1 to the equilibrium state? Explain. Is this a spontaneous process?

Accepted Answer

Identify the nature of the reaction: The dissociation of A_{2}(g) into 2 A(g) involves breaking bonds, which generally requires energy. Thus, the enthalpy change (∆H) for the reaction is likely positive (+), as energy is absorbed to break the bonds in A_{2}(g).. Consider the entropy change (∆S): The reaction results in the formation of more gas particles (from 1 molecule of A_{2} to 2 molecules of A). Increasing the number of gas particles increases the randomness or disorder of the system, suggesting that the entropy change (∆S) is positive (+).. Determine the sign of the Gibbs free energy change (∆G) using the relationship ∆G = ∆H - T∆S. Since ∆H is positive and ∆S is also positive, the temperature (T) will play a crucial role. At high temperatures, the T∆S term may outweigh ∆H, leading to a negative (∆G), which indicates a spontaneous process.. Assess the spontaneity of the process: If ∆G is negative, the process is spontaneous. The temperature dependency must be considered to fully determine spontaneity across different temperatures.. Summarize the signs: ∆H is positive (+), ∆S is positive (+), and ∆G could be negative (-) depending on the temperature, indicating that the reaction could be spontaneous under certain conditions.

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Key Concepts

Enthalpy (∆H)

Entropy (∆S)

Gibbs Free Energy (∆G)