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Chemical Kinetics

This article explores how chemical kinetics and the laws of thermodynamics are used to predict the final equilibrium state of products in a reaction. It discusses the concept of reaction rate, global reactions, reaction mechanisms, the law of mass action, and rate coefficients.

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Chemical Kinetics

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  1. Chemical Kinetics First and Second Laws of thermodynamics are used to predict the final equilibrium state of the products after the reaction is complete. Chemical kinetics deals with how fast the reaction proceeds. How fast the fuel is consumed is of interest, the reaction ratew’’’ is defined as: where [ F ] refers to the fuel concentration (kmol/m3 or kg/m3), negative sign due to the fact that the fuel is consumed. Global (or overall) reactions describe the initial and final states:

  2. Reaction Mechanism In reality the reaction proceeds through elementary reactions in a chain process known as chain reactions The global hydrogen-oxygen reaction proceeds via the following elementary reactions, collectively known as a reaction mechanism: Chain initiation Chain propagation Chain branching Chain termination

  3. Law of Mass Action The law of mass action states that for an elementary reaction the reaction rate is proportional to the product of the concentrations of the reactants present raised to a power equal to the corresponding stoichiometric coefficient. The constant of proportionality is called the reaction rate constant k. For m simultaneous equations:

  4. Law of Mass Action k Applying the law of mass action to the reaction Recall n = 2 A1 = H A2 = H2

  5. Reaction Rate Theory Kinetic theory of gases is used to come up with the following expression for the elementary reaction rate constant, first proposed by Arrhenius where A and b are the rate coefficients, Ea is the activation energy and R is the universal gas constant. Therefore, for the reaction the reaction rate is k The values of a, b and Ea are tabulated for different reactions. This expression indicates that molecular hydrogen is produced faster at higher temperature and at a higher atomic hydrogen concentration.

  6. Rate Coefficients for H2-O2 Reactions AbEa Temperature range Reactions ((cm3/gmol)n-1/s)* (kJ/gmol) (K) * n is the reaction order

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