Arrheniusanalyses

Arrhenius analyses refer to methods used in physical chemistry to study the temperature dependence of chemical reaction rates through the Arrhenius equation. They are used to extract kinetic parameters such as activation energy and the pre-exponential factor from measurements of rate constants at different temperatures.

The Arrhenius equation, k = A exp(-Ea/RT), transforms to a linear form: ln k = ln A - Ea/(R T). Plotting ln k versus 1/T yields a straight line with slope -Ea/R and intercept ln A, allowing Ea and A to be determined from experimental data. Data collection typically involves measuring rate constants at several temperatures under controlled conditions, ensuring a single dominant step.

Interpretation: A linear Arrhenius plot supports a single-rate-determining-step mechanism over the tested range. Deviations from linearity indicate changes in mechanism, temperature-dependent Ea, or contributions from different processes, such as phase transitions, solvent effects, or tunneling at low temperatures. Non-Arrhenius behavior can also arise from complex kinetics or diffusion limitations.

Extensions and alternatives: The modified Arrhenius equation incorporates a temperature-dependent pre-factor, often written k = A T^n exp(-Ea/RT), to account for temperature effects on A. In polymer science and materials chemistry, other representations such as the Vogel–Fulcher–Tammann or transition-state theory equations may be used. Arrhenius analyses remain a standard first step in kinetic studies and in comparing catalysts or materials.

History: Named after Svante Arrhenius, who proposed the exponential dependence of rates on temperature in 1889. The technique is widely taught in chemistry courses and is widely used in catalysis, electrochemistry, corrosion science, and biochemistry to estimate activation barriers and compare kinetic regimes.