26.1.4—The numerical value of a rate constant, e.g

From rate=k[A]^m[B]^n, rearrange k=rate/([A]^m[B]^n). For a first-order reaction, k=0.693/t½.

Use the order determined by evidence, keep concentration units consistent, and report k units that make the rate equation dimensionally correct.

If rate=2.0×10⁻³ mol dm⁻³ s⁻¹ and [A]=0.10 mol dm⁻³ for a first-order reaction, k=2.0×10⁻² s⁻¹; t½=34.7 s.

Do not use 0.693/t½ for a zero- or second-order reaction, and do not calculate k before determining order.