The rate of the reaction?

What is the rate law for this reaction?

• The reaction of benzyl bromide with cyanide ion is given below. When the benzyl bromide concentration is constant and cyanide concentration doubles, the reaction rate increases by a factor of two. When the cyanide concentration is held constant and the benzyl bromide concentration is doubled, the rate of the reaction doubles. What is the rate law for this reaction? A) Rate=k[C6H5CH2Br]^2[CN]^2 B) Rate=k[C6H5CH2Br]^4[CN]^2 C) Rate=k[C6H5CH2Br]^2[CN] D) Rate=k[C6H5CH2Br][CN] Please explain...

• Answer:

  The answer is D) Rate=k[C6H5CH2Br][CN]. If doubling the concentration of one reactant, while holding the others constant, results in a doubling of rate, the reaction is first order with respect to that reactant. If doubling the concentration of one reactant, while holding the others constant, results in a quadrupling of rate, the reaction is second order with respect to that reactant. Finally, if doubling the concentration of one reactant, while holding the others constant, does not affect rate, the reaction is zero order with respect to that reactant.