Recycling back of outlet stream to the reactor from an ideal CSTR carrying out a first order liquid phase reaction will result in __________ in conversion.
A. Decrease
B. Increase
C. No change
D. Either A or B, depends on the type of reaction
Answer: Option C
This Question Belongs to Chemical Engineering >> Chemical Reaction Engineering
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A. $${{\text{k}}_{\text{e}}}{\text{ff}} = {\text{k}} + {{\text{k}}_{\text{g}}}$$
B. $${{\text{k}}_{\text{e}}}{\text{ff}} = \frac{{{\text{k}} + {{\text{k}}_{\text{g}}}}}{2}$$
C. $${{\text{k}}_{\text{e}}}{\text{ff}} = {\left( {{\text{k}}{{\text{k}}_{\text{g}}}} \right)^{\frac{1}{2}}}$$
D. $$\frac{1}{{{{\text{k}}_{\text{e}}}{\text{ff}}}} = \frac{1}{{\text{k}}} + \frac{1}{{{{\text{k}}_{\text{g}}}}}$$
The half life period of a first order reaction is given by (where, K = rate constant. )
A. 1.5 K
B. 2.5 K
C. $$\frac{{0.693}}{{\text{K}}}$$
D. 6.93 K
Catalyst is a substance, which __________ chemical reaction.
A. Increases the speed of a
B. Decreases the speed of a
C. Can either increase or decrease the speed of a
D. Alters the value of equilibrium constant in a reversible
A. $$ \propto {\text{CA}}$$
B. $$ \propto \frac{1}{{{\text{CA}}}}$$
C. Independent of temperature
D. None of these
The correct answer is:
B. Increase
🔍 Explanation:
In an ideal Continuous Stirred Tank Reactor (CSTR) conducting a first-order liquid-phase reaction, recycling a portion of the reactor outlet back to the inlet will:
Increase the reactant residence time in the system.
Expose unconverted reactants to the catalyst/reactive zone multiple times, effectively enhancing conversion.
Make the system behave more like a plug flow reactor (PFR) as the recycle ratio increases — and a PFR gives higher conversion than a CSTR for first-order reactions at the same space time.
💡 Why conversion increases:
In a single CSTR, due to perfect mixing, reactants are immediately diluted with products — leading to lower conversion.
With recycle, the fresh feed is diluted with unconverted reactants, which improves conversion efficiency across the system.
✅ Final Answer:
B. Increase