Question

A reaction was found to be fourth order in A. Increasing the concentration of A by a factor of 2 will cause the reaction rate to increase by a factor of________.

Consider the reaction: 4NH₃ + 7O₂ à 4NO₂ + 6H₂O

Which substance appears the slowest?

		NH3
		O2
		NO2
		H2O

Answer 1

Answer 1. When a reaction is found to be fourth order in A, the rate of the reaction is r=k[A]⁴ . If the concentration of A is doubled, then the rate of the reaction becomes

r​​​​​​'=k[2A]⁴=2⁴ x k[A]⁴= 16 x k[A]⁴= 16r

Thus, the reaction rate increases by a factor of 16 times.

Answer 2. Among all the reaction species, NO2 has the highest molecular weight. According to Boltzmann Maxwell's speed distribution of gas molecules, a molecule having high molecular weight possess higher speed distribution function, G(v) but lesser speed distribution range, v. Therefore, NO2 will appear the slowest.