The approximate mass of present initially in the bulb is — States of Matter and Gaseous State Chemistry Question

💡 Solution & Explanation

At 300 K: P_He = 114 mm Hg, n_He = 0.01 mol. When heated to 600 K, the pressure of He alone is P_He' = 114 × (600 / 300) = 228 mm Hg. The total final pressure is 908 mm Hg, so the pressure due to the decomposition products ($NH_3$ and $HCl$) is P_prod = 908 - 228 = 680 mm Hg. Since P ∝ n at constant V and T, we have: n_prod / n_He = 680 / 228 → n_prod = 0.01 × 680 / 228 = 0.03 mol. Since 1 mole of $NH_4Cl$ decomposes to 2 moles of gas ($NH_3$ + $HCl$), the moles of $NH_4Cl$ originally present is 0.03 / 2 = 0.015 mol. Mass = 0.015 × 53.5 ≈ 0.8 g.