Reaction kinetics

Rates and the Boltzmann distribution

Rate = change in concentration per unit time (gradient of a concentration–time graph). The Boltzmann distribution shows the spread of molecular energies: it starts at the origin, rises to a peak (most probable energy) and tails off without touching the axis. Only molecules with $E\ge E_a$ react. At higher temperature the curve flattens and shifts right; the area beyond $E_a$ grows a lot, so rate increases significantly. A catalyst gives a pathway with lower $E_a$, so more molecules exceed it. Homogeneous catalysts are in the same phase as reactants; heterogeneous catalysts are in a different phase (adsorption on surfaces).