Solid ammonium nitrate decomposes when heated according to
NH₄NO₃(s) → N₂O(g) + 2 H₂O(g)
A 5.00 g sample of NH₄NO₃ is placed in a 2.50 L rigid, evacuated container and heated to a constant temperature. The mass of the remaining solid is measured at various times, giving the following data.
Time (min) | 0 | 2.0 | 4.0 | 6.0 | 8.0
Mass of NH₄NO₃ (g) | 5.00 | 4.26 | 3.62 | 3.12 | 2.76
(The molar mass of NH₄NO₃ is 80.0 g mol⁻¹.)
(a) Convert the masses to moles of NH₄NO₃ at each recorded time. Record your results in a clearly labeled table.
(b) Using your data from part (a), calculate the average rate of disappearance of NH₄NO₃ between 2.0 min and 8.0 min in mol L⁻¹ s⁻¹.
(c) Determine the corresponding average rate of appearance of N₂O(g) during the same interval, stating any assumptions made and showing how stoichiometry is applied.
(d) The student wishes to express the rate from part (c) in terms of the partial pressure of N₂O. Given that the temperature is 350 K, calculate this rate in kPa min⁻¹. (Assume ideal-gas behavior.)
(e) Critique two potential sources of experimental error that could affect the accuracy of the rate calculations in parts (b) and (d). For each, indicate whether the calculated rate would be too high, too low, or unaffected and justify your reasoning.