Question

What is
(a) rate of a reaction ?
(b) rate constant of a reaction ?

Answer 1

a)rate of reaction is the speed which tells how fast the reaction takes place ,
b) rate constant or rate coefficient tell about quantity of rate of reaction  

k we denote rate constant by k 

larger the value of k faster is the reaction similarly smaller the value of k slower is ht reaction .
for different reaction its value varies .
at a fixed temp it is constant .and characteristic to reaction
it is independent of concentration for a particular reaction .

Answer 2

Hey mate...
~~~~~~~~~

a) Rate of Reaction is actually the rate at which reactant gets converted to products. It can be either fast or slow. If a reaction has a low rate, that means the molecules combine at a slower speed than a reaction with a high rate. 

2) It is a constant of proportionality in the rate law equation and is equal to the rate of reaction when the molar concentration of each of the reaction is unity. This is the rate constant of reaction.

^_^