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Chemical Reaction Engineering

Chemical Reaction Engineering. Chapter 3, Part 1: Rate Laws. X. Why a Rate Law?. If we have Then we can size a number of CSTR and PFR reaction systems. Summary. X. X. X. Why a Rate Law?. If we have Then we can size a number of CSTR and PFR reaction systems. 2 CSTRs. CSTR. PFR. X.

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Chemical Reaction Engineering

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  1. Chemical Reaction Engineering Chapter 3, Part 1: Rate Laws

  2. X Why a Rate Law? • If we have • Then we can size a number of CSTR and PFR reaction systems

  3. Summary

  4. X X X Why a Rate Law? • If we have • Then we can size a number of CSTR and PFR reaction systems 2 CSTRs CSTR PFR X

  5. X X X Why a Rate Law? • If we have • Then we can size a number of CSTR and PFR reaction systems • To find -rA= f(X) • Need the rate law, -rA=f(CA, CB) • Need the reaction stoichiometry, CA=CA0(1-X) 2 CSTRs CSTR PFR X

  6. Rate Law Basics • A rate law describes the behavior of a reaction. The rate of a reaction is a function of temperature (through the rate constant) and concentration.

  7. Rate Law Basics • A rate law describes the behavior of a reaction. The rate of a reaction is a function of temperature (through the rate constant) and concentration. • Power Law Model • k is the specific reaction rate (constant)

  8. Rate Law Basics • A rate law describes the behavior of a reaction. The rate of a reaction is a function of temperature (through the rate constant) and concentration. • Power Law Model • k is the specific reaction rate (constant) • k is given by the Arrhenius Equation: • Where: • E = activation energy (cal/mol) • R = gas constant (cal/mol*K) • T = temperature (K) • A = frequency factor (units of A, and k, depend on overall reaction order)

  9. Rate Law Basics • To find the activation energy, plot k as a function of temperature: Where:

  10. Reaction Order • You can tell the overall reaction order by the units of k Reaction Order Rate Law k C -r A A 3 3 (mol/dm ) (mol/dm *s) zero (mol /dm3*s) -r = k A

  11. Reaction Order • You can tell the overall reaction order by the units of k Reaction Order Rate Law k C -r A A 3 3 (mol/dm ) (mol/dm *s) zero (mol /dm3*s) -r = k A -1 1st s -r = kC A A

  12. Reaction Order • You can tell the overall reaction order by the units of k Reaction Order Rate Law k C -r A A 3 3 (mol/dm ) (mol/dm *s) zero (mol /dm3*s) -r = k A -1 1st s -r = kC A A 2nd 2 (dm3 /mol*s) -r = kC A A

  13. Examples of Rate Laws • First Order Reactions (1) Homogeneous irreversible elementary gas phase reaction with

  14. Examples of Rate Laws • First Order Reactions (1) Homogeneous irreversible elementary gas phase reaction with (2) Homogeneous reversible elementary reaction with and

  15. Examples of Rate Laws • First Order Reactions (1) Homogeneous irreversible elementary gas phase reaction with (2) Homogeneous reversible elementary reaction with and • Second Order Reactions (1) Homogeneous irreversible non-elementary reaction with and • This is first order in ONCB, first order in ammonia and overall second order. At 188˚C

  16. Examples of Rate Laws • Second Order Reactions (2) Homogeneous irreversible elementary reaction with

  17. Examples of Rate Laws • Second Order Reactions (2) Homogeneous irreversible elementary reaction This reaction is first order in CNBr, first order in CH3NH2 and overall second order. (3) Heterogeneous catalytic reaction: The following reaction takes place over a solid catalyst: with

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