For the reaction 2NH$_3$(g) $\xrightarrow{\mathrm{Pt}}$ N$_2$ + 3H$_2$(g), Rate = k. i) Write the order and molecularity of this reaction. ii) Write the unit of k.

CBSE Class 12 · 2016 · All India · Chemical KineticsShort Answer

For the reaction 2NH

_{3}

(g)

Pt

_{2}

+ 3H

_{2}

(g), Rate = k.
i) Write the order and molecularity of this reaction.
ii) Write the unit of k.

Answer: (i) Order 0; molecularity 2. (ii) mol L⁻¹ s⁻¹

(i) Rate

= k

means the rate is independent of concentration — order = 0 (the Pt surface is saturated). Two NH

_{3}

molecules take part in the elementary decomposition, so molecularity = 2.
(ii) For zero order,

k

has the units of the rate itself:

mol L^{- 1} s^{- 1}

CBSE Class 12 Board · 2016 · All India · Subjective