Chemical Kinetics and Mechanism

Definitions

• Mechanism: Step-by-step sequence of elementary reactions lead to overall chemical change.

• Rate Law: Mathematical expression linking reaction rate and concentrations.

• Reaction Order: An empirical quantity obtained from measurements of rate.

Rate Definitions

• Speed of Reaction: Determined by the concentration of reaction per unit time. (mol/L)

• Reaction Rate (v): Change in concentration of reactants/products per unit time. (value cannot be negative)

  • Instantaneous Rate: Gradient of concentration vs. time at a specific moment.

  • Initial Rate: Instantaneous rate at the start of a reaction.

  • Average Rate: Over a specific time interval.

Rate Laws and Order

• Rate laws expresses rate in terms of concentration of reactants, products and catalysts.

• Rate Constant (k): Represents the proportionality factor in rate laws. (mol L-1)

• Overall rate order: Sum of powers of concentration terms in the rate law (e.g., v = k[A]²[B], overall order = 3).

• Not all laws and orders correspond to stoichiometric coefficients, must be determined by experiment.