Rapid Calculation of First-Order Rate Constants Processing of kinetic experiments in which several series of reactions are run may absorb many hours with a slide and/or logarithmic tables. A lab experiment involving 30 first-order reactions may take an inexperienced student 5 hr or more to calculate unless comouter-based regression techniaues are available. The usual techniaue in student laboratories is to graph log [el again& time ( t ) ,where [c] is the reactant concentration and obtain the First-order rate constant k as 2.3030og [c,] - log [crJ tz
- t,
A preferable method is to use semilogarithmic paper and obtain
k
= 2.303 log [cJ/[c21
t? - t l so that logarithms need be taken only once in the calculation of each rate constant. Two manipulations of the slide rule then yield the required answer. However, intermediate results have to be temporarily memorized or written down, and the method is tiring. The futher simplification suggested here is to use fixed values of [ex] and [cr], in which case the entire numerator becomes a constant. The reciprocal scale of the slide rule is then permanently set to this constant, and a simple movement of the cursor to the value of ( t 2 - t l ) as rkad directly from the chart, yields the value of k on the reciprocal scale. Allan J. Davison Department of Kinesiolagy Simon Fraser University Burnaby2, B.C. Canada
672
/
Journal of Chemical Education
