Gaseous dinitrogen pentoxide, N2O5, decomposes to form nitrogen dioxide and oxygen gas with the init — Kinetics Chemistry Question
Problem Context
Gaseous dinitrogen pentoxide, N2O5, decomposes to form nitrogen dioxide and oxygen gas with the initial rate data at 25 ˚C given in the table.
Write a balanced equation for this reaction.
Model Answer
2N2O5 → 4NO2 + O2
Use the data provided to write the rate law and calculate the value of k for this reaction. Show all calculations.
Model Answer
The rate will be given by the rate law (Rate=k[N2O5]x) in each case, so by taking the ratio, the rate constant cancels,
means that 2.33^x = 2.33 so x=1. Checking with a second set of data,
leads to 4.33^x = 4.33, confirming that the reaction is first order. Now calculate the rate constant:
so k = 2.28×10-3 min-1 and we have Rate = 2.28×10-3 min-1[N2O5].
Calculate the time required for the concentration of a 0.150 M sample of N2O5 to decrease to 0.050 M.
Model Answer
Use the integrated rate law,
. Plugging in
= ln(3) = (2.28×10^-3 min^-1)t so t = 481 minutes.
The initial rate for the reaction of a 0.150 M sample is 2.37×10–3 mol.L–1.min–1 at 40 ˚C. Determine the activation energy for this reaction.
Model Answer
Use the information from the two temperatures given in the Arrhenus equation:
, so, plugging in values gives :
so ln(6.93) = (Ea / 8.314 J·mol-1·K-1) × (0.00335 - 0.00319) and solving for Ea gives : Ea = 1.00×10^5 J·mol-1 = 100 kJ·mol-1. (Note that using rates, rather than rate constants in the argument of the natural log is an alternative, correct method.)