The study of reaction kinetics provides essential information about details of chemical reactions. H — Physical Chemistry — Kinetics Chemistry Question
Reaction Kinetics
The study of reaction kinetics provides essential information about details of chemical reactions. Here the formation of NO and its reaction with oxygen is considered.
The formation of NO takes place according to the equation:
2 NOCl(g) 2 NO(g) + Cl2(g)
The rate constant k = 2.6×10–8 dm3 mol–1 s–1 at 300 K and 4.9×10–4 dm3 mol–1 s–1 at 400 K. The gas constant R = 8.314 J mol–1 K–1.
Calculate the activation energy for the NO formation using the Arrhenius equation.
Model Answer
Due to the Arrhenius equation: log k = log A – Ea / 2.3 RT
we can substitute the values of k and T:
log k1 = log A – Ea / 2.3 RT1, log k2 = log A – Ea / 2.3 RT2
Subtraction gives:
log k1 – log k2 = – Ea / 2.3 R (1/T1 - 1/T2)
Ea = 98.225 kJ mol-1
The reaction of NO with oxygen is as follows:
2 NO(g) + O2(g) 2 NO2(g)
Give the rate equation for the NO2 formation on basis of this mechanism.
Experimentally, the rate equation reads s = k [NO]2 [O2]
Model Answer
The slow step is the rate determining; this is the second reaction.
The expression for s is: d[NO2]/dt = k [NO3][NO]
The equilibrium gives: K = k1/k-1 = [NO3] / ([NO][O2])
Rewritten this is: [NO3] = K [NO][O2]
Substitution gives for s: s = k2 K [NO]2 [O2]
Which conclusion do you draw?
The proposed mechanism is incorrect.
The proposed mechanism is correct.
The experiment is non-conclusive.
Mark the correct answer.
Model Answer
The proposed mechanism is correct.