An industrial process for manufacturing sulfuric acid involves the sequence below
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
An industrial process for manufacturing sulfuric acid involves the sequence below.
Step 1 S(s)+O2(g)→SO2(g) (large, negative ΔG)
Step 2 SO2(g)+21O2(g)⇌SO3(g) (catalyzed)
Step 3 SO3(g)+H2SO4(l)→H2S2O7(l) (oleum formation)
Assume all steps occur in separate vessels connected by valves that can be opened or closed as needed, and the temperature remains constant at 450 °C.
(a) For each of the three steps, identify whether the step is treated as reversible or irreversible in routine plant operation. Support each classification by referring to thermodynamic or practical considerations relevant to the step.
(b) Sketch (labeling axes clearly) the qualitative time dependence of the partial pressure of SO3 during continuous operation in which Steps 1–3 proceed sequentially and continuously. Indicate on the sketch the portions corresponding to each step and any plateau regions.
(c) A new catalyst is introduced that accelerates both the forward and reverse reactions of Step 2 equally. Predict the effect, if any, on (i) the equilibrium composition achieved in Step 2 and (ii) the overall rate of SO3 consumption in Step 3. Justify your predictions.
(d) Considering your answers above, evaluate whether the entire three-step sequence can attain a single overall dynamic equilibrium state under the stated operating conditions. Provide a reasoned argument that references the reversibility of individual steps and the coupling between vessels.