Question

Which reactor operates under unsteady-state conditions?

• A. Continuous stirred tank reactor
• B. Plug flow reactor
• C. Batch reactor
• D. Tubular reactor

Hint:

Logic Tip: A continuous reactor (CSTR/PFR) is like a flowing river; it always looks the same at a given spot. A Batch reactor is like baking a cake in an oven; the batter is constantly changing into cake over the 30 minutes it is inside. "Changing over time" = Unsteady-state.

Answer 1

The Correct Option is C

Concept:
In chemical reaction engineering, reactors are classified by their mode of operation: continuous vs. batch. This distinction dictates whether their internal conditions change over time (unsteady-state) or remain constant (steady-state).

Step 1: In a steady-state system, variables like concentration, temperature, and reaction rate at any specific spatial point inside the reactor do not change as time passes.

Step 2: A Continuous Stirred Tank Reactor (CSTR) and a Plug Flow Reactor (PFR/Tubular) are designed for continuous flow. Once they reach their design operating conditions, the concentrations at the inlet, middle, and outlet remain perfectly constant indefinitely (steady-state).

Step 3: In a Batch reactor, reactants are loaded into a closed vessel, mixed, and allowed to react for a specific duration. No material enters or leaves during this time.

Step 4: Because the reactants are continuously being consumed and turned into products over that duration, the concentration of chemicals inside the batch reactor is constantly changing from minute to minute. Therefore, it inherently operates under unsteady-state (transient) conditions.