Tables of Conversion Factors for Reaction Rate Constants
D. D. Drysdale
and A. C. L I O Y ~ The University Leeds, 2, England
T h e rate (R) of a reaction can be expressed as a function of the concentrations of the reactant species which, for element,ary processes at least, is of the form R = k[AIc [B]'. . . where [XI is the concentration of reactant X. The order of the reaction is then defined as the sum n = a b . . . and k is known as the nt,h order rate constant.' A continual source of annoyance to the physical chemist lies in the wide variet.y of unit,s used in t,he presentation of rate constants for a given order of reaction. This is a consequence of the various concentration units that are commonly employed, and the students must surely be confused and discouraged by this lack of uniformity. Indeed, mistakes have been made in the literature in the conversion of kinetic data from one set of units to anot,her. A collection of conversion factors is of great value to anyone lrith interest in chemical kinetics. A different table is required for each order of reaction. However, it should be noted that a conversion table is unnecessary for first order rate constants because the units (normally seer') are independent of the units in which concentrations have been expressed. We have chosen to show the generalized form in Table 1, and in
+
+
x 10-"-1
(mm H p ) P
16.03
atm-L
12.18 X
8ee-L
10-"-1
8e.-1
'S.I. unita. 54
/
Table 2 the numerical values of the conversion factors for second-order rate constants are given. To convert a rate constant from one set of units A to a new set B. one can find the conversion factor vertically below A and in the horizontal row B in the appropriatc table; thus if a second-order rate constant is quoted in units of cm'particle-I sec-I, it can he converted to 1molc-I sec-I by multiplying by 6.023 X 10". The symbols used in Table 1 are as follows: No, Avogedro's number (6.023 X loz3particles mole-'); Vo,the molar volume (22,414 cm3mole-'); T,the absolute temperature. I t has frequently been suggested that some uniformity be introduced to the presentation of rate constant dat,a, but it seems unlikely that this ideal situation could be attained without considerable resistance. In some cases, just~ificationcan be found for making use of a part,icular set. of units which would be of convenience to an author during the course of his work. Thus rate c?nstants expressed in units of mm-' sec-' in a constant t,emperaturcsyst,em2facilitate rapid calculation of t,hc rates of individual reactions within that system at, different pressnrcs of reactants. T l ~ w m ~ \ ~ - l ~ l r tA.i ~F., i ~ "Gas s o ~ Kincties," , Butterwol.ths S c i e h f i c Puhlicatiotw, 1955, Chapter 1.
Journal of Chemical Education
For. example, KIMIWI.L, G . H. .mo L~cllou,1). J., Can. J .
c h m , 38, 1714(10~1).
16.03 X 10-T-1
16.03 T-L
12.18 T-1
12.18 X
1OJT-'
96.53 X
10"T-'
73.36 X 10'T-1
.. .
1.316 X 10-8
760
...
