First-order reaction

From Wikipedia, the free encyclopedia
Jump to: navigation, search

First-order reaction may refer to:

  • Order of reaction, in chemical kinetics, the power to which the concentration term of a certain reactant in the rate equation is raised
  • Rate equation#First-order reaction, a reaction that depends on the concentration of only one reactant. Mathematically,

\frac{dC}{dt} =-kC

Solving the above differential equation, we get

C=C_ie^{-kt}

From Arrhenius equation,

k=k_0e^{\frac{-E_a}{RT}}

     t   = time in seconds (s)
     C  = the concentration of the reactant (mol/m^3, other units are also used, e.g. kg/m^3)
     C_i  = the initial concentration of the reactant (mol m^{-3})
     k_0 = pre-exponential factor (1/s)
     E_a = the activation energy (J/mol)
     k  = reaction rate constant (1/s) which is usually described by the Arrhenius equation: .
     R  = the universal gas constant (J/mol.K, K is temperature in kelvin not to be confused with little k, the reaction constant)