ChE 324: Kinetics Chapter 6 Quiz
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Questions and Answers

What is the primary strategy to maximize the production of product D?

  • Increase the concentration of A significantly
  • Use a batch reactor efficiently
  • Utilize a PFR/PBR and select appropriate spacetime (correct)
  • Use a CSTRs in series (correct)

    • In the reaction involving A, B, and C, what is the net reaction rate for species B?

  • -rB = k1CA + k2CB
  • -rB = k2CB
  • rB,net = k1CA - k2CB (correct)
  • rB,net = k2CA - k1CB

    • How does the concentration of A depend on spacetime τ in a PFR?

  • CA = k1C0e^(-τ)
  • CA = CA0e^(-k1τ) (correct)
  • CA = CA0(1 - e^(-k1τ))
  • dFA/dV = k1C0e^(-k1τ)

    • What must be determined to quench the reaction when the concentration of B is at its maximum?

    <p>The time (or spacetime) necessary for the reaction</p> Signup and view all the answers

    What is the effect of k1 on the concentration of A as described in the equations?

    <p>Higher k1 decreases the concentration of A faster</p> Signup and view all the answers

    What characterizes parallel or competing reactions?

    <p>Multiple reactions use the same limiting reactant.</p> Signup and view all the answers

    Why can't conversions be used in the analysis of multiple reactions?

    <p>Each reaction may have its own limiting reactant.</p> Signup and view all the answers

    Which of the following best describes series reactions?

    <p>A reaction depends on the completion of the previous reaction.</p> Signup and view all the answers

    What is an essential factor to consider when selecting a reactor for multiple reactions?

    <p>Concentration requirements of each reaction.</p> Signup and view all the answers

    What type of reaction involves more than one reactant yielding a complex product?

    <p>Complex reactions</p> Signup and view all the answers

    In independent reactions, how are the reactants characterized?

    <p>They can occur in parallel without influencing one another.</p> Signup and view all the answers

    Which of these is NOT a characteristic of multiple reactions?

    <p>Shared kinetics for all reactions.</p> Signup and view all the answers

    What is the role of a limiting reactant in a series reaction?

    <p>It defines the maximum yield of all products.</p> Signup and view all the answers

    What is the rate expression for the disappearance of A in the reactor?

    <p>$-r_A = k_B + k_C C_A$</p> Signup and view all the answers

    If the initial concentration of A ($C_{A0}$) is 4 mol/L, what is the concentration of A when XA = 0.9?

    <p>0.4 mol/L</p> Signup and view all the answers

    What is the value of the residence time ($ au$) when XA = 0.9?

    <p>0.92 min</p> Signup and view all the answers

    Which reaction condition leads to a higher yield of B?

    <p>Higher residence time</p> Signup and view all the answers

    What factor is emphasized as key in the context of series reactions?

    <p>Time</p> Signup and view all the answers

    In calculating the mole balance on A, which equation is utilized?

    <p>$ rac{dC_A}{d au} = -r_A$</p> Signup and view all the answers

    At a concentration of C_A = 0.4 mol/L, what is the yield of B?

    <p>$0.51$</p> Signup and view all the answers

    How does the yield of B in the CSTR compare to other reactors?

    <p>It is better but has a longer residence time.</p> Signup and view all the answers

    What is the expression for the overall yield of B in a PFR?

    <p>$ ilde{Y}<em>B = rac{C_B}{C</em>{A0} - C_A}$</p> Signup and view all the answers

    When integrating the mass balance for B, what value does dV correspond to in terms of dτ?

    <p>$dV = r_B imes d au$</p> Signup and view all the answers

    In the context of a CSTR, what is the relationship between the yield of B and the conversion of A at 90%?

    <p>Yield of B approaches a maximum as the conversion of A nears 100%.</p> Signup and view all the answers

    What is the initial concentration of A given in the reactions?

    <p>$4 ext{ mol/L}$</p> Signup and view all the answers

    At 90% conversion of A, what is the expected concentration of B produced in a PFR?

    <p>$3.6 ext{ mol/L}$</p> Signup and view all the answers

    How is the rate of formation of B represented mathematically?

    <p>$r_B = k_B C_A^2$</p> Signup and view all the answers

    What factor affects the yield of B when using a CSTR compared to a PFR?

    <p>Residence time in the reactor</p> Signup and view all the answers

    Which of the following equations correctly represents the rate of change of A in terms of its concentration?

    <p>$- rac{dC_A}{d au} = 2k_B + k_C$</p> Signup and view all the answers

    What does the expression $dCB/d\tau$ represent in the context of the equation?

    <p>The rate of change of concentration of C with respect to time</p> Signup and view all the answers

    Under what condition does the optimal reactor volume $V_{opt}$ occur?

    <p>When $dCB/dt = 0$</p> Signup and view all the answers

    Which components of the system influence the expression for $dCB/d\tau$?

    <p>Both reaction rates $k_1$, $k_2$ and initial concentration $CA0$</p> Signup and view all the answers

    What relationship does $\tau_{opt} = \frac{1}{k_1 - k_2} \ln \frac{k_2}{k_1}$ suggest about the reaction rates?

    <p>Increasing $k_1$ decreases the optimal time.</p> Signup and view all the answers

    What does the equation $CB = \frac{k_1 CA0}{k_2 - k_1} (e^{-k_1 \tau} - e^{-k_2 \tau})$ define?

    <p>The concentration of C at any time</p> Signup and view all the answers

    In the expression $V_{opt} = \tau_{opt} \cdot \upsilon_0$, what does $\upsilon_0$ represent?

    <p>The flow rate of the reactants</p> Signup and view all the answers

    Which condition results in the maximum concentration of B according to the equations provided?

    <p>When reaction rates are equal</p> Signup and view all the answers

    What mathematical method is applicable for solving $dCB$ in terms of $d\tau$?

    <p>Using an integrating factor</p> Signup and view all the answers

    How is the concentration of reactant A represented in the context of reaction equations?

    <p>CA = CA0 - CB</p> Signup and view all the answers

    What is the expression for the yield of B in a Continuous Stirred Tank Reactor (CSTR)?

    <p>$\tilde{Y}_B = \frac{FB}{CA0 - CA}$</p> Signup and view all the answers

    At 90% conversion of A, what is required to determine the concentration of B (CB) in a CSTR?

    <p>Mole balance on A</p> Signup and view all the answers

    How is the rate of formation of B (rB) expressed in terms of concentration and time?

    <p>rB = $\frac{CB}{τ}$</p> Signup and view all the answers

    What is the relationship between the input and output flow rates for component A in a steady-state process?

    <p>Input minus output equals generation rate</p> Signup and view all the answers

    If the initial concentration of A (CA0) is 4 mol/L and the conversion of A is 90%, what is the remaining concentration of A (CA)?

    <p>0.6 mol/L</p> Signup and view all the answers

    Which factor does not play a role in the calculation of yield (YB) in a CSTR?

    <p>Temperature of the surroundings</p> Signup and view all the answers

    What represents the conversion of A at which the mole balance on A is evaluated?

    <p>XA = 0.9</p> Signup and view all the answers

    In the context of a PFR, how does the yield of B change with higher conversion rates of A?

    <p>It increases proportionally</p> Signup and view all the answers

    Study Notes

    Chapter 6: Multiple Reactions

    • This chapter, part of the ChE 324: Kinetics and Reactor Design (A) course, focuses on multiple reactions.
    • Multiple reactions occur simultaneously, influencing each other and the products formed.
    • Multiple reactions analysis is similar to single reactions, but conversion (X) cannot be used directly.

    Reasons for Not Using Conversion (X)

    • Multiple reactions often have more than one limiting reactant, unlike single reactions.
    • Conversion is defined relative to the limiting reactant for a particular reaction. Thus, a reactant limiting in one reaction may not limit another.
    • Multiple reactions imply more than one conversion value.

    Classification of Multiple Reactions

    • Parallel (competing): Reactions occur simultaneously, competing for reactants. Examples include parallel or competing reactions.
    • Series: Reactions occur sequentially, one after another, with the product of one reaction being the reactant for the next. Examples include series reactions.
    • Independent/Complex: Reactions aren't directly related. Examples include independent/complex reactions. These include crude oil cracking and complex reactions.

    Concentration Requirements and Reactor Selection

    • Plug Flow Reactor (PFR): Reactant concentration is high initially and decreases progressively towards the outlet.
    • Continuous Stirred Tank Reactor (CSTR): Reactant concentration is consistently low at the reactor outlet.
    • Semi-batch: Concentration of one reactant is high initially and decreases progressively. The concentration of the other reactants remains consistent.

    Review: Multiple Reactions & Selectivity

    • Selectivity (SD/U): The ratio of the rate of formation of the desired product (D) to the rate of formation of the undesired product (U.)

      • Instantaneous selectivity, SD/U
      • Overall selectivity, SD/U

    • Yield (YD): The ratio of the moles of the desired product to the moles of the reactant at a specific operating time or point.

      • Instantaneous yield (YD)
      • Overall yield (YD)

    • Goal: Maximize selectivity and yield to enhance desired product formation.

    Additional Topics

    • More complex calculations for determining yields in various reactor types (CSTR, PFR).
    • Detailed analysis of consecutive reactions.
    • Optimizing reactor design parameters for maximum desired product formation in series reactions.

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    Related Documents

    Chapter 6: Multiple Reactions CHE 324 Fall 2024 PDF

    Description

    Test your understanding of multiple reactions in kinetics and reactor design. This chapter explores how multiple reactions interact and influence each other, along with the challenges of analyzing them. Dive into the concepts of parallel and series reactions and the reasons conversion cannot be used directly.

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