Chemical Kinetics Overview

Rates of Chemical Reactions

• Reaction rate reflects the speed of reactant consumption or product formation.
• Rate is quantified as the change in concentration over time.
• Rate Law relates the rate of a reaction to the rate constant and reactant concentrations.
• Reaction orders indicate how the rate depends on the concentration of reactants.

Spontaneity and Reaction Speed

• A reaction is spontaneous if the Gibbs free energy change (∆G) is negative.
• Spontaneity indicates thermodynamic favorability, not speed.
• Example: The transformation of diamond to graphite is spontaneous but extremely slow.

Rate Equation

• General form of the rate equation: Rate = k(reactants).
• Differential rate law example: (-\frac{d[A]}{dt} = k[A][B]).
• The rate constant (k) is specific to each reaction and influenced by various factors.

Empirical Observations of Reaction Rates

• Observing how reactant and product concentrations change over time is fundamental in kinetics.
• L. Wilhelm's study in 1850 laid groundwork through the inversion of sucrose with a polarimeter.
• Various methods for measuring concentration include spectrophotometry and potentiometry.

Concentration Over Time

• As a reaction progresses, reactant concentration decreases while product concentration increases.
• Intermediate species may appear and then disappear during reaction progress.

Rate Change and Stoichiometry

• For a generalized reaction (aA + bB \rightarrow cC + dD), the rate law reflects the relationship between reactants and products.
• The rate at which products form is calculated as (\frac{1}{c} \frac{d[C]}{dt} = f[A][B][C][D]).
• Rates for other species are related by the stoichiometric coefficients.

Order of Reaction

• Overall order of a reaction is the sum of the powers of reactants in the rate law.
• Reaction order indicates how the rate depends on each reactant's concentration.

Experimental Determination of Reaction Order

• For the reaction: (F_2(g) + 2 ClO_2(g) \rightarrow 2FClO_2(g)), data collection includes concentration values and initial rates for various experiments.
• Initial rate dependence on ([F_2]) and ([ClO_2]) can help deduce reaction orders.