Calculation of the decomposition temperature of NH4Cl

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I saw an online calculation for the decomposition temperature of the reaction NH4Cl(s) = NH2(g) + HCl(g). The process is as follows: The standard enthalpies of formation are NH3 – 46.11 KJ/mol, HCl – 92.31 KJ/mol, and NH4Cl – 314.43 KJ/mol. Thus, ΔH(298K) = –46.11 – 92.31 + 314.43 = 176.01 KJ/mol; the reaction is endothermic. The standard entropies are NH3: 192.45 J/mol·K, HCl: 186.99 J/mol·K, and NH4Cl: 94.6 J/mol·K. Therefore, ΔS(298K) = 192.45 + 186.99 – 94.6 = 285 J/mol·K. If test tubes are used, the partial pressure of each gas is 0.5. Then, 0 = ΔG + RT * ln(0.5 * 0.5) = ΔH – T * ΔS + RT * ln(0.5 * 0.5). Substituting the values, T = 176.01 KJ/mol * 1000 J/KJ = 594 K. The reasoning behind the calculation seems correct; there is only a small issue: ΔG in this calculation is based on a temperature of 298 K. To determine the decomposition temperature, shouldn’t ΔG at that temperature be used? ΔG should change at different temperatures. I can’t remember my thermodynamics knowledge clearly; please give me some guidance!