Specific Rate Constant
Definition and meaning of Specific Rate Constant in chemistry.
The specific rate constant (k) is the proportionality constant in a rate law that relates the reaction rate to the concentrations of reactants. It is independent of concentration but highly dependent on temperature.
In more detail
The specific rate constant appears in rate expressions such as rate = k[A]m[B]n. Its units depend on the overall reaction order: a first-order reaction has k in s-1, while a second-order reaction has k in L mol-1 s-1. Temperature dramatically affects k, typically described by the Arrhenius equation, k = Ae-Ea/RT, where Ea is activation energy. The term "specific" emphasizes that the constant is unique to a particular reaction system.
Key facts
| Symbol | k |
|---|---|
| Units | depend on reaction order |
| Temperature dependence | follows Arrhenius equation |
| Field | Physical Chemistry |
For the reaction 2NO + O2 → 2NO2, experimental data give rate = k[NO]2[O2], with k ≈ 7.1 × 103 L2 mol-2 s-1 at 25°C.
Frequently asked questions
Why is it called the 'specific' rate constant?
The term 'specific' indicates the constant is unique to a particular chemical reaction and given temperature. Different reactions and different temperatures yield different rate constants.
How does the specific rate constant differ from reaction rate?
Reaction rate is the speed at which reactants convert to products and varies as concentrations change. The rate constant k is fixed for given conditions and is used in the rate law to calculate the instantaneous rate.