Chapter 5, Problem 5.48P

The oxidation of nitric oxide

   $\text{NO+}\frac{\text{1}}{\text{2}}{\text{O}}_{\text{2}}\rightleftharpoons {\text{NO}}_{\text{2}}$

takes place in an isothermal batch reactor at 25°C. The reactor is charged with a mixture containing 20.0 volume percent NO and the balance air at an initial pressure of 380 kPa (absolute).

(a) Assuming ideal-gas behavior, determine the composition of the mixture (component mole fractions) and the ?nal pressure (kPa) if the conversion of NO is 90%.

(b) Suppose the pressure in the reactor eventually equilibrates (levels out) at 360 kPa. What is the equilibrium percent conversion of NO? Calculate the reaction equilibrium constant at the prevailing temperature, $K_p\left[{\left(\text{atm}\right)}^{-0.5}\right]$, de?ned as

   $K_p=\frac{\left(p_{{\text{NO}}_{\text{2}}}\right)}{\left(p_{\text{NO}}\right){\left(p_{{\text{O}}_{\text{2}}}\right)}^{0.5}}$

where p_i(atm) is the partial pressure of species i (NO₃, NO, O₂) at equilibrium.

(c) Assuming that K_Pdepends only on temperature, estimate the ?nal pressure and composition in the reactor if the feed ratio of NO to O₂and the initial pressure are the same as in Part (a), but the feed to the reactor is pure O₂instead of air.

(d) Replace the partial pressures in the expression for K_P, and use the result to explain how reactor pressure in?uences the conversion of NO to NO₂.