Question
Chemistry Question on Chemical Kinetics
The rate law for the decomposition of hydrogen iodide is - = d[HI]/dt = k[HI]2. The units of rate constant k are:
L mol-1 s-1
L-1 mol s-1
L2 mol-2 s-1
L1/2 mol1/2 s-1
L mol-1 s-1
Solution
The correct option is: (A): L mol-1 s-1
The given rate law is −dtd[HI]=k[HI]2, where k is the rate constant and [HI] represents the concentration of hydrogen iodide. The units of the rate constant k can be determined by analyzing the units on both sides of the equation.
On the left side of the rate law, d[HI] represents the rate of change of concentration with respect to time, which has units of L⋅smol (moles per liter per second) as it's a change in concentration over time.
On the right side of the equation, 2[HI]2 represents the square of the concentration of hydrogen iodide, which has units of 2(Lmol)2 (moles per liter squared).
In order for both sides of the equation to have the same units, the units of the rate constant k must be such that when multiplied by 2[HI]2, it results in the units of the left side (L⋅smol).
Hence, the units of the rate constant k are L⋅smol, which is represented as L mol−1 s−1L mol−1 s−1.
This justification confirms that the answer "L mol-1 s-1" is appropriate for the units of the rate constant k.