Final answer:
To calculate the standard Gibbs free energy change (ΔG°) at 298 K for a reaction, you need the equilibrium constant (Kp) and the temperature. However, the value of Kp is not provided in the question.
Step-by-step explanation:
The equilibrium constant, represented as Kp, can be used to calculate the standard Gibbs free energy change (ΔG°) for a given reaction at a specific temperature. The equation for the reaction is 2HCl(g) ⇌ H₂(g) + Cl₂(g). To calculate ΔG°, we need to know the value of Kp and the temperature at which the calculation is being done. Unfortunately, the value of Kp is not provided in the question. We would need this information to proceed with the calculation.