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first order reaction

A first order reaction depends on the concentration of only one reactant (a unimolecular reaction). Other reactants can be present, but each will be zero order. The rate law for a reaction that is first order with respect to a reactant A is

k is the first order rate constant, which has units of 1/s or s−1.

The integrated first order rate law is

A plot of  vs. time t gives a straight line with a slope of

  .

The half-life of a first order reaction is independent of the starting concentration and is given by

.



Unit of rate constant for first order reaction ( k) = min–1 or s-1
  • The rate constant of a first order reaction has only time unit. It has no concentration unit.
  • This means the numerical value of k for a first order reaction is independent of the unit in which concentration is expressed.
  • If concentration unit is changed the numerical value of k for a first order reaction will not change.
  • However, it would change with  change in time unit. Say, k is 6.0\times 10–3 min then it may also be written as 1\times10–4 s–1 i.e. numerical value of k will decrease 60 times if time unit is changed from however to minute or from minute to second.




first order reaction|second order reaction|rate of reaction Matt Vince