R2.2 How fast? The rate of chemical changeIB Chemistry SL: Flashcards

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Define rate of reaction.

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Define rate of reaction.: The change in concentration of a reactant or product per unit time (mol dm⁻³ s⁻¹).
Define activation energy, Ea.: The minimum energy colliding particles need for a successful collision leading to a reaction.
Two conditions for a successful collision?: Energy ≥ Ea and the correct orientation (collision geometry).
How is average kinetic energy related to temperature?: It is proportional to the absolute temperature in kelvin.
Why does a small temperature rise have a big effect on rate?: A much larger proportion of particles have E ≥ Ea; collision frequency increases only slightly.
Effect of higher temperature on the Maxwell–Boltzmann curve?: Peak lower and shifted to higher energy; area unchanged; more area beyond Ea.
Effect of a catalyst on the Maxwell–Boltzmann curve?: Curve unchanged; Ea moves to lower energy, so more particles have E ≥ Ea.
How does a catalyst work?: It provides an alternative pathway with a lower activation energy.
Does a catalyst change ΔH?: No: reactant and product energies are unchanged.
Ea(reverse) for an exothermic reaction?: Ea(forward) + |ΔH|.
Why does powder react faster than lumps?: Larger surface area, so more frequent collisions.
Why does increasing gas pressure increase rate?: More molecules per unit volume, so more frequent collisions.
If a fixed amount of product is timed, how is rate related to time?: Rate ∝ 1/time.