First-order reaction

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A first-order reaction is a reaction that proceeds at a rate that depends linearly on only one reactant concentration.

Differential Rate Law[edit]

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:

Rate = k[A]1

where k is the rate constant, which can only be found through experimental data.

Integrated Rate Law[edit]

The integrated first order rate law with respect to a reactant A is:

ln[A] = -kt + ln[A0]

where k is the rate constant. The law is also commonly written as:

 The linear, negative slope of a first order reaction.
The linear, negative slope of a first order reaction.

[A] = [A0]e−kt

When graphed on a plane of [Concentration] vs. Time (s−1), a first order reaction will have a graph with a negativeThe half-life formula for a first-order reaction is as follows: t1/2 =ln2 * k-1e, linear slope.

Half-Life[edit]

t(1/2)=0.693/k half life of first order reaction does not depend on reactant concentration.