Question

Which among the following reactions is elementary?

(a) A + B → R; (-rA) = k CACB

(b) 2A + B → R; (-rA) = k CA^2

(c) 2A + B → R; (-rA) = k CACB^2

(d) A + B → R; (-rA) = k CB

The question was posed to me by my school teacher while I was bunking the class.

The query is from Reaction Rates in division Basic Concepts of Chemical Reaction Engineering

Answer 1

Right choice is (a) A + B → R; (-rA) = k CACB

Explanation: Elementary reactions are the ones in which rate equation corresponds to stoichiometry. For the reaction A + B → R, 1 mole of A and 1 mole of B take part in the reaction. Hence, the rate equation has to be

(-rA) = k CA^1CB^1.