Follow material quantities through two explicitly defined reaction stages.
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Method and worked examples
Treat a multistage process in sequence. First calculate the amount reacting in a stage from its feed and conversion. Apply that stage’s balanced mole ratio to find product, then pass the stated stream to the next stage. Do not apply a second-stage conversion to the original feed when the intermediate has a different amount.
For A→2B followed by 2B→C, complete overall conversion gives one C per A. Multiplying independent stage conversions gives overall conversion only after respecting these ratios and transfer assumptions. A recycle stream is unreacted feed returned for another pass. Keep fresh feed, reacted amount and recycled amount separate, and apply energy per mole to the specified reacting or entering amount.
Example 1
100 mol A enters A→2B at 90% conversion. All B enters 2B→C at 80% B conversion. Find C.
Stage 1 reacts 90 mol A and forms 180 mol B. Stage 2 reacts 0.80×180=144 mol B, forming 2144=72 mol C. Overall conversion to C is 72% of the 100 mol maximum.
Example 2
Find unreacted A and B for that process, assuming complete separation and no losses.
Unreacted A=100−90=10 mol. Unreacted B after stage 2=180−144=36 mol. These streams can be separated from product for the stated recycling treatment.
Watch out:The percentage applies to that stage’s specified B feed; calculate the intermediate stream before applying it.
Multistage feed, conversion and recycle data practice | Year 12 Chemistry | Ascent Arcade