Nitrogen dioxide is produced industrially by the thermal oxidation of nitric oxide according to the overall reaction
2 NO(g) + O₂(g) → 2 NO₂(g)
An engineer must determine how reaction temperature affects the rate in a pilot-scale continuous-flow reactor while keeping other variables constant.
(a) Identify two experimental variables other than temperature that must be held constant to ensure that any change in the measured rate can be attributed solely to temperature.
(b) Design a detailed procedure for collecting rate data at 320 K, 340 K, and 360 K in the continuous-flow reactor. Your design should specify how temperature will be controlled and how reaction rate will be quantified from measurable reactor outputs.
(c) After performing the experiment, the engineer obtains the following steady-state conversion data:
Temperature (K) | Fraction of NO converted per pass
320 | 0.18
340 | 0.27
360 | 0.36
Using these data, calculate the relative rate increase (expressed as a multiple of the 320 K rate) at 340 K and at 360 K. Assume constant residence time and ideal plug-flow behavior.
(d) The engineer observes that the percentage increase in rate between 340 K and 360 K is smaller than the percentage increase between 320 K and 340 K. Provide two plausible chemical or engineering explanations for this non-linear temperature dependence.
(e) Recommend one operational modification, other than further temperature adjustment, that could compensate for the diminished rate increase at higher temperatures, and justify how it would enhance the overall production rate of NO₂.