Rate constants are crucial in understanding chemical reactions. They tell us how fast a reaction happens at a specific temperature. These constants link reaction speed to the amount of reactants present, helping us predict how quickly chemicals will transform.
Knowing rate constants lets us compare reaction speeds and figure out how temperature affects them. We can calculate these constants from experiments, watching how reactant amounts change over time. This knowledge is key for controlling reactions in labs and industries.
Rate Constants
Definition of rate constant
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Proportionality constant [k](https://www.fiveableKeyTerm:k) relates reaction rate to reactant concentrations
Specific to a particular reaction at a given temperature
Units depend on overall reaction order
: s−1 (reciprocal seconds)
with rate law rate=k[A][B]: M−1s−1 (reciprocal molar-seconds)
Second-order reaction with rate law rate=k[A]2: M−1s−1 (reciprocal molar-seconds)
Zero-order reaction: Ms−1 (molar per second)
Significance in reaction rates
Determines reaction speed at given temperature and reactant concentrations
Larger k indicates faster reaction, smaller k indicates slower reaction
Intrinsic property of reaction depends on factors like reactant nature, catalysts, and temperature
Used in rate law equation to calculate reaction rate
First-order reaction example: rate=k[A], [A] is reactant A concentration
Temperature dependence via Arrhenius equation
Arrhenius equation relates to temperature: k=Ae−[Ea](https://www.fiveableKeyTerm:ea)/RT
A: pre-exponential factor related to reactant molecule collision frequency
Ea: , minimum energy for reaction to occur
R: universal gas constant (8.314 J/mol·K)
T: absolute temperature (K)
Rate constant increases exponentially with increasing temperature
Higher temperature leads to more molecules with energy to overcome activation energy barrier
Activation energy and pre-exponential factor determined from slope and y-intercept (ln(k) vs. 1/T)
Calculation from experimental data
Rate constant calculated by measuring reactant or product concentrations over time