difference between Activity and selectivity of catalyst.

Activity and selectivity are the two important aspects of heterogeneous catalyst.These can be defined as-
Activity – It is the ability of catalysts to accelerate chemical reactions and the degree of acceleration can be as high as 10¹⁰ times in certain reactions.A good example of catalytic activity is the reaction of H₂ and O₂ in the presence of platinum to form water with explosive violence while their mixtures can be stored indefinitely without any reaction in the absence of catalyst.
Selectivity – It is the ability of catalysts to direct reaction to yield particular products.For ex- n-heptane selectively gives toluene on a platinum catalyst.