CHE 156: L/S Reaction Rate Expression
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Questions and Answers

What influences slow reactions in gas/porous catalyst systems?

  • Surface Kinetics (correct)
  • Film Mass Transfer
  • Particle Temperature Gradients
  • Pore Diffusion

    • What is the order in which effects intrude in liquid systems?

  • 1, 2, 3, and 4
  • 1, 2, 5, and rarely 3 and/or 4 (correct)
  • 1, 4, 2, and 3
  • 1, 3, 2, and 4

    • What is adsorption?

  • A process by which a chemical component is dissolved in a liquid
  • A process by which a chemical component is transformed into a gas
  • A process by which a chemical component is released from a solid phase
  • A process by which a chemical component from a fluid phase is removed by attachment to a solid phase (correct)

    • What is the primary factor limiting the overall rate in faster reactions?

    <p>Particle ∆T and/or Film ∆T</p> Signup and view all the answers

    In which type of systems does Surface Kinetics dominate in slow reactions?

    <p>Gas/porous catalyst systems</p> Signup and view all the answers

    What is the difference between adsorption and absorption?

    <p>Adsorption is a process that occurs at the surface, while absorption is a process that occurs throughout the material</p> Signup and view all the answers

    In heterogeneous catalytic reactions, what is the role of the catalyst?

    <p>To accelerate the reaction rate</p> Signup and view all the answers

    What is the name of the phenomenon where a chemical component from a fluid phase is removed by attachment to a solid phase?

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

    What type of heterogeneous reactions involve the interaction between a gas and a solid?

    <p>Gas-Solid Reactions</p> Signup and view all the answers

    What must be considered when writing rate expressions for heterogeneous reactions?

    <p>Both mass transfer terms and chemical kinetics terms</p> Signup and view all the answers

    How many types of heterogeneous reactions are mentioned in the text?

    <p>3</p> Signup and view all the answers

    What is the result of the burning of a carbon particle in air?

    <p>CO2</p> Signup and view all the answers

    How many rate steps are involved in aerobic fermentation?

    <p>More than 2</p> Signup and view all the answers

    Why is it important to consider mass transfer terms in heterogeneous reactions?

    <p>To account for the movement of material from phase to phase</p> Signup and view all the answers

    What is the unit of the rate of reaction in the equation dNA / dt?

    <p>moles/s</p> Signup and view all the answers

    What is the function of a catalyst in a chemical reaction?

    <p>To speed up the reaction rate</p> Signup and view all the answers

    What is the term for the ability of a catalyst to promote a specific reaction?

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

    What type of catalyst is typically used in biochemical systems?

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

    What is the process by which a reactant attaches to the surface of a catalyst?

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

    What is the purpose of a support in a supported catalyst?

    <p>To increase the surface area of the catalyst</p> Signup and view all the answers

    What is the characteristic of a catalyst that allows it to emerge from a reaction unchanged?

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

    What is the type of catalyst that is typically encountered in processes where pressure drop and heat removal are major considerations?

    <p>Monolithic catalyst</p> Signup and view all the answers

    What is the term for the phenomenon where a reactant attaches to the surface of a catalyst, but does not react?

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

    What is the type of catalyst that is composed of minute particles of active material dispersed over a less active substance?

    <p>Supported catalyst</p> Signup and view all the answers

    Study Notes

    L/S Reaction Rate Expression

    • The reaction rate expression for a liquid-solid (L/S) reaction is derived from the flux of A to the surface and the reaction rate at the surface.
    • The flux of A to the surface is given by: 𝑟𝐴1 = -𝐷𝐶𝐴𝑙 - 𝐶𝐴𝑠 / ∆𝑥
    • The reaction rate at the surface is given by: 𝑟𝐴2 = 𝑘″𝐶𝐴
    • At steady state, the two rates are equal: 𝑟𝐴1 = 𝑟𝐴2

    Rate Expression Rearrangement

    • Rearranging the rate expression equations, we get: 𝑘𝑙𝐶𝐴𝑙 - 𝐶𝐴𝑠 = 𝑘″𝐶𝐴
    • Solving for 𝐶𝐴𝑠, we get: 𝐶𝐴𝑠 = 𝑘𝑙 / (𝑘𝑙 + 𝑘″) 𝐶𝐴𝑙

    Overall Rate Expression

    • The overall rate expression is: 𝑟𝐴 = 𝑘𝑜𝑣𝑒𝑟𝑎𝑙𝑙 𝐶𝐴𝑙 / (1 + 𝑘𝑙 / 𝑘″)

    Catalysts

    • A catalyst is a substance that speeds up a reaction without being consumed by the reaction.
    • There are two broad classes of catalysts: homogeneous and heterogeneous.
    • Enzymes are a type of catalyst that operate at close to ambient temperature with biochemical systems.

    Types of Catalysts

    • Porous catalysts have a large surface area and are used in processes where pressure drop and heat removal are major considerations.
    • Monolithic catalysts are normally encountered in processes where pressure drop and heat removal are major considerations.
    • Supported catalysts consist of minute particles of an active material dispersed over a less active substance called support.
    • Molecular sieves are a type of catalyst that allows selective reactions to occur.

    Factors Influencing Reaction Rate

    • Film diffusion resistance or concentration gradients across the gas film surrounding the particle can influence the reaction rate.
    • Pore diffusion can slow the reaction rate in faster reactions.
    • Surface kinetics alone can influence the reaction rate in slow reactions.
    • Particle ΔT and/or Film ΔT can enter the picture in faster reactions.

    Adsorption on Solid Surfaces

    • Adsorption is a process by which a chemical component from a fluid phase is removed by attachment to a solid phase.
    • Adsorption is an important step in heterogeneous catalytic reactions.

    Heterogeneous Reactions

    • Types of heterogeneous reactions include gas-solid, liquid-solid, and solid-solid reactions.
    • Rate expressions for heterogeneous reactions must consider mass transfer terms in addition to chemical kinetics terms.
    • No single rate expression has general application to all heterogeneous reactions.

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    Description

    This quiz is about developing the overall rate expression for the liquid-solid reaction that takes place on a flat surface, involving diffusion and flux of reactant A.

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