Question

The rate constant of a reaction possesses the units of time⁻¹. What is the order of reaction?

Answer 1

If the rate constant (k) has units of time⁻¹ (i.e., s⁻¹ min⁻¹, etc.), it corresponds to a first-order reaction.

For a general reaction of order n:

Rate = k[A]ⁿ

Units of rate = mol L⁻¹ s⁻¹

Units of [A]ⁿ = (mol L⁻¹)ⁿ

So,

\[\ce{Units of k = \frac{mol L^{-1}s^{-1}}{(mol L^{-1})^n}}\]

= mol¹⁻ⁿ Lⁿ⁻¹ s⁻¹

Now, if the units of k = s⁻¹, then:

mol¹⁻ⁿ Lⁿ⁻¹ = 1

⇒ n = 1

∴ Order of reaction is 1