For conversion of compound A → B, the rate constant of the reaction was found to be 4.6×10⁻⁵ L mol⁻¹ s⁻¹. The order of the reaction is ____________.

Solution

Chemistry ma’am · 3 steps

The units of k tell you the order: L mol⁻¹ s⁻¹ means second order.

1. Units depend on order. For a reaction of order n, rate = k[A]ⁿ. Rate is always in mol L⁻¹ s⁻¹, so the units of k change with n.

   units of k = (mol L⁻¹)¹⁻ⁿ s⁻¹

2. Match the units. Here k is in L mol⁻¹ s⁻¹ = (mol L⁻¹)⁻¹ s⁻¹. So 1 - n = -1, which gives n = 2.
3. So. The reaction is second order. The order is 2.

The common slip: 0. Taking L mol⁻¹ s⁻¹ as the zero-order unit gives 0. Zero order has mol L⁻¹ s⁻¹, with the concentration part the other way up.

The idea to keep. Units of k give the order: (mol L⁻¹)¹⁻ⁿ s⁻¹. So s⁻¹ is first order and L mol⁻¹ s⁻¹ is second order.

Answer from the NTA final answer key. Solution by PrepWiser.