The experimental data for decomposition of N2O5 [2N2O5→4NO2+O2] in gas phase at 318 K are given below:
t/s040080012001600200024002800320010−2×[N2O5]/1.631.361.140.930.780.640.530.430.35mol L−1
Plot [N2O5] against t
t/s040080012001600200024002800320010−2×[N2O5]/1.631.361.140.930.780.640.530.430.35mol L−1
Find the half-life period for the reaction
t/s040080012001600200024002800320010−2×[N2O5]/1.631.361.140.930.780.640.530.430.35mol L−1
Draw a graph between log[N2O5] and t
t/s040080012001600200024002800320010−2×[N2O5]/1.631.361.140.930.780.640.530.430.35mol L−1
What is the rate law?
t/s040080012001600200024002800320010−2×[N2O5]/1.631.361.140.930.780.640.530.430.35mol L−1
Calculate the rate constant
t/s040080012001600200024002800320010−2×[N2O5]/1.631.361.140.930.780.640.530.430.35mol L−1
Calculate the half-life period from k and compare it with (ii)
The plot of [N2O5] against time is given below.
Initial concentration of N2O5=1.63×10−2M
Half of initial concentration
=1.63×10−22=0.815×10−2M
Half-life period = Time corresponding to the above amount in the graph = 1400 s (approximately)
For graph between log[N2O5] and time, we first find the values of log[N2O5].
Time (s)0400800120016002000240028003200[N2O5]×10−21.631.361.140.930.780.640.530.430.35log[N2O5]−1.79−1.87−1.94−2.03−2.11−2.19−2.28−2.37−2.46
Since, the graph between log[N2O5] and time is a straight line, the reaction is of first order.
The rate law:Rate =k[N2O5]
Slope of the time =−k2.303=−2.46−(−1.79)3200−0=−0.673200−k2.303=−0.673200k=0.67×2.3033200
or k=4.82×10−4 s−1
Half-life period (t12)=0.693k=0.6934.82×10−4 s−1=1438s
Half-life period (t12) as calculated from the formula and slope are approximately the same.