Chemical Reaction Kinetics

Collision theory, activation energy, and rate laws

Collision theory: reactions occur when molecules collide with sufficient energy (≥ Ea) and correct orientation. The Arrhenius equation (k = Ae^(-Ea/RT)) shows that rate constant k increases exponentially with temperature — doubling every ~10°C is a rough rule of thumb. The Maxwell-Boltzmann distribution shows the fraction of molecules with enough energy to react — higher T shifts the curve right, increasing the fraction above Ea. Catalysts provide an alternative reaction pathway with lower Ea, increasing the reaction rate without being consumed. Rate orders: zero-order ([A] vs t = linear), first-order (ln[A] vs t = linear, t₁/₂ constant), second-order (1/[A] vs t = linear, t₁/₂ ∝ 1/[A]).