(a) *describe the effect of concentration, pressure, particle size and temperature on the rates ofbr reactions and explain these effects in terms of collisions between reacting particlesbr (b) defi ne the term catalyst and describe the effect of catalysts (including enzymes) on the rates ofbr reactionsbr (c) *explain how pathways with lower activation energies account for the increase in rates of reactionsbr (d) state that transition elements and their compounds act as catalysts (see 8.