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Questions and Answers
What influences slow reactions in gas/porous catalyst systems?
What is the order in which effects intrude in liquid systems?
What is adsorption?
What is the primary factor limiting the overall rate in faster reactions?
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In which type of systems does Surface Kinetics dominate in slow reactions?
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What is the difference between adsorption and absorption?
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In heterogeneous catalytic reactions, what is the role of the catalyst?
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What is the name of the phenomenon where a chemical component from a fluid phase is removed by attachment to a solid phase?
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What type of heterogeneous reactions involve the interaction between a gas and a solid?
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What must be considered when writing rate expressions for heterogeneous reactions?
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How many types of heterogeneous reactions are mentioned in the text?
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What is the result of the burning of a carbon particle in air?
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How many rate steps are involved in aerobic fermentation?
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Why is it important to consider mass transfer terms in heterogeneous reactions?
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What is the unit of the rate of reaction in the equation dNA / dt?
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What is the function of a catalyst in a chemical reaction?
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What is the term for the ability of a catalyst to promote a specific reaction?
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What type of catalyst is typically used in biochemical systems?
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What is the process by which a reactant attaches to the surface of a catalyst?
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What is the purpose of a support in a supported catalyst?
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What is the characteristic of a catalyst that allows it to emerge from a reaction unchanged?
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What is the type of catalyst that is typically encountered in processes where pressure drop and heat removal are major considerations?
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What is the term for the phenomenon where a reactant attaches to the surface of a catalyst, but does not react?
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What is the type of catalyst that is composed of minute particles of active material dispersed over a less active substance?
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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.
