Rate Constant - Full Explanation
1. Definition:
The rate constant (k) is a proportionality factor in the rate equation of a chemical reaction.
It determines the speed of a reaction under given conditions.
2. Rate Law and Rate Constant:
For a general reaction: aA + bB -> cC + dD
The rate law is: Rate = k [A]^m [B]^n
where:
- k = rate constant
- [A] & [B] = concentrations of reactants
- m & n = reaction order with respect to A and B
3. Units of Rate Constant:
The units of k depend on the order of reaction:
Zero Order: Rate = k, Unit: mol L^-1 s^-1
First Order: Rate = k[A], Unit: s^-1
Second Order: Rate = k[A]^2 or k[A][B], Unit: L mol^-1 s^-1
Third Order: Rate = k[A]^3 or k[A]^2[B], Unit: L^2 mol^-2 s^-1
4. Temperature Dependence (Arrhenius Equation):
The rate constant k changes with temperature according to the Arrhenius Equation:
k = A * e^(-Ea / RT)
where:
- A = frequency factor
- Ea = activation energy
- R = gas constant (8.314 J mol^-1 K^-1)
- T = temperature (K)
1. Definition:
The rate constant (k) is a proportionality factor in the rate equation of a chemical reaction.
It determines the speed of a reaction under given conditions.
2. Rate Law and Rate Constant:
For a general reaction: aA + bB -> cC + dD
The rate law is: Rate = k [A]^m [B]^n
where:
- k = rate constant
- [A] & [B] = concentrations of reactants
- m & n = reaction order with respect to A and B
3. Units of Rate Constant:
The units of k depend on the order of reaction:
Zero Order: Rate = k, Unit: mol L^-1 s^-1
First Order: Rate = k[A], Unit: s^-1
Second Order: Rate = k[A]^2 or k[A][B], Unit: L mol^-1 s^-1
Third Order: Rate = k[A]^3 or k[A]^2[B], Unit: L^2 mol^-2 s^-1
4. Temperature Dependence (Arrhenius Equation):
The rate constant k changes with temperature according to the Arrhenius Equation:
k = A * e^(-Ea / RT)
where:
- A = frequency factor
- Ea = activation energy
- R = gas constant (8.314 J mol^-1 K^-1)
- T = temperature (K)
