816:. The order of reaction is an empirical quantity determined by experiment from the rate law of the reaction. It is the sum of the exponents in the rate law equation. Molecularity, on the other hand, is deduced from the mechanism of an elementary reaction, and is used only in context of an elementary reaction. It is the number of molecules taking part in this reaction.
800:
Catalytic reactions are often three-component, but in practice a complex of the starting materials is first formed and the rate-determining step is the reaction of this complex into products, not an adventitious collision between the two species and the catalyst. For example, in hydrogenation with a
1167:
On the other hand, the molecularity of this reaction is undefined, because it involves a mechanism of more than one step. However, we can consider the molecularity of the individual elementary reactions that make up this mechanism: the first step is trimolecular because it involves three reactant
801:
metal catalyst, molecular dihydrogen first dissociates onto the metal surface into hydrogen atoms bound to the surface, and it is these monatomic hydrogens that react with the starting material, also previously adsorbed onto the surface.
990:
equal the sum of reactant stoichiometric coefficients, the reaction must involve more than one step. The proposed two-step mechanism has a rate-limiting first step whose molecularity corresponds to the overall order of 3:
75:
The kinetic order of a complex (multistep) reaction, however, is not necessarily equal to the number of molecules involved. The concept of molecularity is only useful to describe elementary reactions or steps.
619:
793:
911:
1079:
251:
514:
1237:
Temkin, O. N. State-of-the-Art in the Theory of
Kinetics of Complex Reactions. In Homogeneous Catalysis with Metal Complexes: Kinetic Aspects and Mechanisms, John Wiley and Sons, ltd, 2012
1163:
745:
360:
As can be deduced from the rate law equation, the number of A molecules that decay is proportional to the number of A molecules available. An example of a unimolecular reaction, is the
685:
427:
116:
980:
1349:
145:
349:
286:
1430:
318:
372:
519:
Here, the rate of the reaction is proportional to the rate at which the reactants come together. An example of a bimolecular reaction is the
544:
61:) and correct orientation. Depending on how many molecules come together, a reaction can be unimolecular, bimolecular or even trimolecular.
1642:
749:
804:
Reactions of higher molecularity are not observed due to very small probability of simultaneous interaction between 4 or more molecules.
1519:
828:
1476:
1202:
997:
1783:
1423:
1400:
1323:
1280:
1255:
797:
These reactions frequently have a pressure and temperature dependence region of transition between second and third order kinetics.
1084:
84:
In a unimolecular reaction, a single molecule rearranges atoms, forming different molecules. This is illustrated by the equation
709:
1691:
1686:
1496:
697:
a second reaction with a third body is required. After the initial bimolecular collision of A and B an energetically excited
1851:
1856:
645:
398:
1416:
177:
701:
is formed, then, it collides with a M body, in a second bimolecular reaction, transferring the excess energy to it.
1877:
1821:
1511:
434:
1548:
1448:
528:
1778:
1182:
162:
1826:
1627:
1367:
Carr, R. W. Chemical
Kinetics. In Encyclopedia of Applied Physics. WILEY-VCH Verlag GmbH & Co KGaA, 2003
1581:
1192:
354:
1811:
1743:
1601:
1591:
698:
90:
1806:
1534:
629:
1816:
1748:
1733:
1676:
1339:
1187:
633:
379:
150:
46:
918:
1841:
1611:
1440:
390:
In a bimolecular reaction, two molecules collide and exchange energy, atoms or groups of atoms.
371:
1376:
Rogers, D. W. Chemical
Kinetics. In Concise Physical Chemistry, John Wiley and Sons, Inc. 2010.
126:
1836:
1831:
1793:
1738:
1657:
1637:
1573:
1396:
1319:
1276:
1251:
813:
58:
1768:
1717:
1671:
1388:
1168:
molecules, while the second step is bimolecular because it involves two reactant molecules.
295:
72:
of an elementary reaction can therefore be determined by inspection, from the molecularity.
327:
1846:
1758:
1707:
261:
1553:
1542:
532:
303:
1871:
1801:
1773:
1681:
1632:
1606:
1335:
1311:
1177:
536:
361:
291:
169:
158:
154:
69:
50:
1559:
1466:
1456:
820:
365:
1712:
1647:
1291:
1197:
1356:, a semiempirical expression for the rate constant of termolecular reactions
1763:
1408:
38:
17:
1228:
Atkins, P.; de Paula, J. Physical
Chemistry. Oxford University Press, 2014
694:
54:
31:
1357:
640:
is also used to refer to three body association reactions of the type:
636:, with appropriate orientation and sufficient energy. However the term
690:
168:
In either case, the rate of the reaction or step is described by the
664:
1666:
64:
The kinetic order of any elementary reaction or reaction step is
1412:
1486:
520:
27:
Number of molecules that participate in a single-step reaction
45:
is the number of molecules that come together to react in an
704:
The reaction can be explained as two consecutive reactions:
370:
819:
This difference can be illustrated on the reaction between
1148:
1128:
1112:
1099:
1067:
1054:
1038:
1022:
964:
893:
873:
857:
591:
559:
632:
or gas mixtures involves three reactants simultaneously
614:{\displaystyle {\ce {CH3Br + OH^- -> CH3OH + Br^-}}}
1087:
1000:
921:
831:
808:
Difference between molecularity and order of reaction
788:{\displaystyle {\ce {AB}}^{*}{\ce {+ M -> C + M}}}
752:
712:
648:
547:
437:
401:
330:
306:
264:
180:
129:
93:
57:
in the elementary reaction with effective collision (
689:
Where the M over the arrow denotes that to conserve
1792:
1726:
1700:
1656:
1620:
1572:
1533:
1510:
1447:
1157:
1073:
974:
906:{\displaystyle {\ce {2NO + 2H2 -> N2 + 2H2O,}}}
905:
787:
739:
679:
613:
508:
421:
343:
312:
280:
245:
139:
110:
1074:{\displaystyle {\ce {2 NO + H2 -> N2 + H2O2}}}
812:It is important to distinguish molecularity from
246:{\displaystyle {\frac {d\left}{dt}}=-k_{r}\left,}
431:which corresponds to the second order rate law:
378:Unimolecular reactions can be explained by the
509:{\displaystyle {\frac {d}{dt}}=-k_{r}{\ce {}}}
1424:
1271:J.I. Steinfeld, J.S. Francisco and W.L. Hase
628:A termolecular (or trimolecular) reaction in
8:
1158:{\displaystyle {\ce {H2O2 + H2 -> 2H2O}}}
165:if there is more than one product molecule.
161:if there is only one product molecule, or a
1267:
1265:
1263:
1431:
1417:
1409:
1384:
1382:
740:{\displaystyle {\ce {A + B -> AB}}^{*}}
1147:
1142:
1137:
1127:
1122:
1111:
1106:
1098:
1093:
1088:
1086:
1066:
1061:
1053:
1048:
1037:
1032:
1021:
1016:
1005:
1001:
999:
963:
958:
950:
944:
933:
931:
920:
892:
887:
882:
872:
867:
856:
851:
846:
836:
832:
830:
765:
759:
754:
751:
731:
714:
711:
665:
659:
649:
647:
604:
590:
585:
572:
558:
553:
548:
546:
494:
483:
482:
476:
447:
438:
436:
402:
400:
335:
329:
305:
269:
268:
263:
231:
221:
191:
181:
179:
131:
130:
128:
94:
92:
1395:(3rd ed., Harper & Row 1987), p.277
1224:
1222:
1220:
1218:
1310:as alternative names is J.W. Moore and
1214:
1457:Unimolecular nucleophilic substitution
1250:(4th ed., Allyn and Bacon 1983) p.215
393:This can be described by the equation
1467:Bimolecular nucleophilic substitution
680:{\displaystyle {\ce {A + B -> C}}}
422:{\displaystyle {\ce {A + B -> P}}}
7:
1520:Electrophilic aromatic substitution
1275:(2nd ed., Prentice Hall 1999) p.5,
1487:Nucleophilic internal substitution
1477:Nucleophilic aromatic substitution
1203:Reaction progress kinetic analysis
270:
132:
111:{\displaystyle {\ce {A -> P,}}}
25:
1318:(3rd ed., John Wiley 1981) p.17,
1302:One textbook which mentions both
47:elementary (single-step) reaction
1643:Lindemann–Hinshelwood mechanism
915:where the observed rate law is
1692:Outer sphere electron transfer
1687:Inner sphere electron transfer
1497:Nucleophilic acyl substitution
1273:Chemical Kinetics and Dynamics
1131:
1025:
967:
951:
940:
934:
860:
772:
724:
578:
501:
495:
490:
484:
452:
444:
412:
273:
265:
98:
1:
1857:Diffusion-controlled reaction
1292:IUPAC Gold Book: Molecularity
975:{\displaystyle v=k{\ce {^2}}}
68:to its molecularity, and the
1246:Morrison R.T. and Boyd R.N.
1512:Electrophilic substitutions
1338:for termolecular reactions
51:stoichiometric coefficients
49:and is equal to the sum of
1894:
1822:Energy profile (chemistry)
1784:More O'Ferrall–Jencks plot
1449:Nucleophilic substitutions
982:, so that the reaction is
29:
1852:Michaelis–Menten kinetics
529:nucleophilic substitution
140:{\displaystyle {\rm {P}}}
1779:Potential energy surface
1658:Electron/Proton transfer
1543:Unimolecular elimination
1183:Dissociation (chemistry)
30:Not to be confused with
1827:Transition state theory
1628:Intramolecular reaction
1554:Bimolecular elimination
986:. Since the order does
1621:Unimolecular reactions
1582:Electrophilic addition
1316:Kinetics and Mechanism
1193:Crossed molecular beam
1159:
1075:
976:
907:
789:
741:
681:
624:Termolecular reactions
615:
510:
423:
375:
355:reaction rate constant
345:
314:
282:
247:
141:
112:
80:Unimolecular reactions
1812:Rate-determining step
1744:Reactive intermediate
1602:Free-radical addition
1592:Nucleophilic addition
1535:Elimination reactions
1160:
1076:
977:
908:
790:
742:
699:reaction intermediate
682:
616:
511:
424:
386:Bimolecular reactions
380:Lindemann-Hinshelwood
374:
346:
344:{\displaystyle k_{r}}
315:
283:
248:
142:
113:
1807:Equilibrium constant
1085:
998:
919:
829:
750:
710:
646:
545:
435:
399:
328:
304:
262:
178:
170:first order rate law
127:
91:
1817:Reaction coordinate
1749:Radical (chemistry)
1734:Elementary reaction
1677:Grotthuss mechanism
1441:reaction mechanisms
1188:Lindemann mechanism
1150:
1130:
1114:
1101:
1069:
1056:
1040:
1024:
966:
895:
875:
859:
670:
593:
561:
149:refers to chemical
1842:Arrhenius equation
1612:Oxidative addition
1574:Addition reactions
1155:
1138:
1118:
1102:
1089:
1071:
1057:
1044:
1028:
1012:
972:
954:
903:
883:
863:
847:
785:
737:
677:
611:
581:
549:
506:
419:
376:
341:
310:
281:{\displaystyle }}}
278:
243:
153:. The reaction or
137:
108:
1878:Chemical kinetics
1865:
1864:
1837:Activated complex
1832:Activation energy
1794:Chemical kinetics
1739:Reaction dynamics
1638:Photodissociation
1393:Chemical Kinetics
1248:Organic Chemistry
1153:
1141:
1121:
1105:
1092:
1060:
1047:
1031:
1015:
1008:
957:
939:
898:
886:
866:
850:
839:
814:order of reaction
783:
777:
771:
757:
729:
723:
717:
675:
671:
668:
658:
652:
603:
596:
584:
571:
564:
552:
500:
489:
464:
450:
417:
411:
405:
313:{\displaystyle t}
234:
209:
194:
103:
97:
59:sufficient energy
16:(Redirected from
1885:
1769:Collision theory
1718:Matrix isolation
1672:Harpoon reaction
1549:E1cB-elimination
1433:
1426:
1419:
1410:
1403:
1389:Keith J. Laidler
1386:
1377:
1374:
1368:
1365:
1359:
1347:
1341:
1334:Text discussing
1332:
1326:
1300:
1294:
1289:
1283:
1269:
1258:
1244:
1238:
1235:
1229:
1226:
1164:
1162:
1161:
1156:
1154:
1151:
1149:
1146:
1139:
1129:
1126:
1119:
1113:
1110:
1103:
1100:
1097:
1090:
1080:
1078:
1077:
1072:
1070:
1068:
1065:
1058:
1055:
1052:
1045:
1039:
1036:
1029:
1023:
1020:
1013:
1006:
981:
979:
978:
973:
971:
970:
965:
962:
955:
949:
948:
943:
937:
912:
910:
909:
904:
902:
896:
894:
891:
884:
874:
871:
864:
858:
855:
848:
837:
794:
792:
791:
786:
784:
781:
775:
769:
764:
763:
758:
755:
746:
744:
743:
738:
736:
735:
730:
727:
721:
715:
686:
684:
683:
678:
676:
673:
672:
669:
666:
660:
656:
650:
620:
618:
617:
612:
610:
609:
608:
601:
594:
592:
589:
582:
577:
576:
569:
562:
560:
557:
550:
515:
513:
512:
507:
505:
504:
498:
493:
487:
481:
480:
465:
463:
455:
451:
448:
439:
428:
426:
425:
420:
418:
415:
409:
403:
352:
350:
348:
347:
342:
340:
339:
321:
319:
317:
316:
311:
289:
287:
285:
284:
279:
277:
276:
252:
250:
249:
244:
239:
235:
232:
226:
225:
210:
208:
200:
199:
195:
192:
182:
148:
146:
144:
143:
138:
136:
135:
117:
115:
114:
109:
107:
101:
95:
21:
1893:
1892:
1888:
1887:
1886:
1884:
1883:
1882:
1868:
1867:
1866:
1861:
1847:Eyring equation
1788:
1759:Stereochemistry
1722:
1708:Solvent effects
1696:
1652:
1616:
1597:
1587:
1568:
1563:
1529:
1525:
1506:
1502:
1492:
1482:
1472:
1462:
1443:
1437:
1407:
1406:
1387:
1380:
1375:
1371:
1366:
1362:
1354:Troe expression
1348:
1344:
1333:
1329:
1301:
1297:
1290:
1286:
1270:
1261:
1245:
1241:
1236:
1232:
1227:
1216:
1211:
1174:
1083:
1082:
996:
995:
932:
917:
916:
827:
826:
810:
753:
748:
747:
713:
708:
707:
644:
643:
626:
600:
568:
543:
542:
524:
472:
456:
440:
433:
432:
397:
396:
388:
331:
326:
325:
323:
302:
301:
299:
260:
259:
257:
227:
217:
201:
187:
183:
176:
175:
125:
124:
122:
89:
88:
82:
35:
28:
23:
22:
15:
12:
11:
5:
1891:
1889:
1881:
1880:
1870:
1869:
1863:
1862:
1860:
1859:
1854:
1849:
1844:
1839:
1834:
1829:
1824:
1819:
1814:
1809:
1804:
1798:
1796:
1790:
1789:
1787:
1786:
1781:
1776:
1771:
1766:
1761:
1756:
1751:
1746:
1741:
1736:
1730:
1728:
1727:Related topics
1724:
1723:
1721:
1720:
1715:
1710:
1704:
1702:
1701:Medium effects
1698:
1697:
1695:
1694:
1689:
1684:
1679:
1674:
1669:
1663:
1661:
1654:
1653:
1651:
1650:
1645:
1640:
1635:
1630:
1624:
1622:
1618:
1617:
1615:
1614:
1609:
1604:
1599:
1595:
1589:
1585:
1578:
1576:
1570:
1569:
1567:
1566:
1561:
1557:
1551:
1546:
1539:
1537:
1531:
1530:
1528:
1527:
1523:
1516:
1514:
1508:
1507:
1505:
1504:
1500:
1494:
1490:
1484:
1480:
1474:
1470:
1464:
1460:
1453:
1451:
1445:
1444:
1438:
1436:
1435:
1428:
1421:
1413:
1405:
1404:
1378:
1369:
1360:
1352:definition of
1342:
1336:rate constants
1327:
1295:
1284:
1259:
1239:
1230:
1213:
1212:
1210:
1207:
1206:
1205:
1200:
1195:
1190:
1185:
1180:
1173:
1170:
1145:
1136:
1133:
1125:
1117:
1109:
1096:
1064:
1051:
1043:
1035:
1027:
1019:
1011:
1004:
969:
961:
953:
947:
942:
936:
930:
927:
924:
901:
890:
881:
878:
870:
862:
854:
845:
842:
835:
823:and hydrogen:
809:
806:
780:
774:
768:
762:
734:
726:
720:
663:
655:
625:
622:
607:
599:
588:
580:
575:
567:
556:
533:methyl bromide
522:
503:
497:
492:
486:
479:
475:
471:
468:
462:
459:
454:
446:
443:
414:
408:
387:
384:
338:
334:
309:
275:
272:
267:
254:
253:
242:
238:
230:
224:
220:
216:
213:
207:
204:
198:
190:
186:
134:
119:
118:
106:
100:
81:
78:
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
1890:
1879:
1876:
1875:
1873:
1858:
1855:
1853:
1850:
1848:
1845:
1843:
1840:
1838:
1835:
1833:
1830:
1828:
1825:
1823:
1820:
1818:
1815:
1813:
1810:
1808:
1805:
1803:
1802:Rate equation
1800:
1799:
1797:
1795:
1791:
1785:
1782:
1780:
1777:
1775:
1774:Arrow pushing
1772:
1770:
1767:
1765:
1762:
1760:
1757:
1755:
1752:
1750:
1747:
1745:
1742:
1740:
1737:
1735:
1732:
1731:
1729:
1725:
1719:
1716:
1714:
1711:
1709:
1706:
1705:
1703:
1699:
1693:
1690:
1688:
1685:
1683:
1682:Marcus theory
1680:
1678:
1675:
1673:
1670:
1668:
1665:
1664:
1662:
1659:
1655:
1649:
1646:
1644:
1641:
1639:
1636:
1634:
1633:Isomerization
1631:
1629:
1626:
1625:
1623:
1619:
1613:
1610:
1608:
1607:Cycloaddition
1605:
1603:
1600:
1593:
1590:
1583:
1580:
1579:
1577:
1575:
1571:
1565:
1558:
1555:
1552:
1550:
1547:
1544:
1541:
1540:
1538:
1536:
1532:
1521:
1518:
1517:
1515:
1513:
1509:
1498:
1495:
1488:
1485:
1478:
1475:
1468:
1465:
1458:
1455:
1454:
1452:
1450:
1446:
1442:
1434:
1429:
1427:
1422:
1420:
1415:
1414:
1411:
1402:
1401:0-06-043862-2
1398:
1394:
1390:
1385:
1383:
1379:
1373:
1370:
1364:
1361:
1358:
1355:
1351:
1346:
1343:
1340:
1337:
1331:
1328:
1325:
1324:0-471-03558-0
1321:
1317:
1313:
1309:
1305:
1299:
1296:
1293:
1288:
1285:
1282:
1281:0-13-737123-3
1278:
1274:
1268:
1266:
1264:
1260:
1257:
1256:0-205-05838-8
1253:
1249:
1243:
1240:
1234:
1231:
1225:
1223:
1221:
1219:
1215:
1208:
1204:
1201:
1199:
1196:
1194:
1191:
1189:
1186:
1184:
1181:
1179:
1178:Reaction rate
1176:
1175:
1171:
1169:
1165:
1143:
1134:
1123:
1115:
1107:
1094:
1062:
1049:
1041:
1033:
1017:
1009:
1002:
992:
989:
985:
959:
945:
928:
925:
922:
913:
899:
888:
879:
876:
868:
852:
843:
840:
833:
824:
822:
817:
815:
807:
805:
802:
798:
795:
778:
766:
760:
732:
718:
705:
702:
700:
696:
692:
687:
661:
653:
641:
639:
635:
631:
623:
621:
605:
597:
586:
573:
565:
554:
540:
538:
537:hydroxide ion
534:
530:
526:
517:
477:
473:
469:
466:
460:
457:
441:
429:
406:
394:
391:
385:
383:
381:
373:
369:
367:
363:
362:isomerization
358:
356:
336:
332:
322:is time, and
307:
297:
293:
292:concentration
240:
236:
228:
222:
218:
214:
211:
205:
202:
196:
188:
184:
174:
173:
172:
171:
166:
164:
160:
159:isomerization
156:
155:reaction step
152:
104:
87:
86:
85:
79:
77:
73:
71:
70:rate equation
67:
62:
60:
56:
52:
48:
44:
40:
33:
19:
1754:Molecularity
1753:
1392:
1372:
1363:
1353:
1345:
1330:
1315:
1312:R.G. Pearson
1308:trimolecular
1307:
1304:termolecular
1303:
1298:
1287:
1272:
1247:
1242:
1233:
1166:
993:
987:
983:
914:
825:
821:nitric oxide
818:
811:
803:
799:
796:
706:
703:
688:
642:
638:trimolecular
637:
627:
541:
518:
430:
395:
392:
389:
377:
368:to propene:
366:cyclopropane
359:
255:
167:
163:dissociation
120:
83:
74:
65:
63:
43:molecularity
42:
36:
18:Unimolecular
1713:Cage effect
1648:RRKM theory
1564:elimination
1198:Cage effect
984:third order
382:mechanism.
1209:References
151:product(s)
1764:Catalysis
1660:reactions
1132:⟶
1026:⟶
861:⟶
773:⟶
761:∗
733:∗
725:⟶
634:colliding
630:solutions
606:−
579:⟶
574:−
470:−
413:⟶
215:−
99:⟶
55:reactants
39:chemistry
1872:Category
1172:See also
695:momentum
662:→
32:Molarity
353:is the
351:
324:
320:
300:
296:species
290:is the
288:
258:
147:
123:
1439:Basic
1399:
1322:
1279:
1254:
1081:Fast:
994:Slow:
691:energy
527:-type
256:where
157:is an
121:where
1667:Redox
1503:Acyl)
1350:IUPAC
66:equal
1556:(E2)
1545:(E1)
1397:ISBN
1320:ISBN
1306:and
1277:ISBN
1252:ISBN
693:and
1526:Ar)
1483:Ar)
988:not
535:by
531:of
364:of
298:A,
294:of
53:of
37:In
1874::
1594:(A
1584:(A
1522:(S
1499:(S
1493:i)
1489:(S
1479:(S
1473:2)
1469:(S
1463:1)
1459:(S
1391:,
1381:^
1314:,
1262:^
1217:^
1007:NO
938:NO
838:NO
756:AB
728:AB
602:Br
595:OH
583:CH
570:OH
563:Br
551:CH
539::
516:.
357:.
41:,
1598:)
1596:N
1588:)
1586:E
1562:i
1560:E
1524:E
1501:N
1491:N
1481:N
1471:N
1461:N
1432:e
1425:t
1418:v
1152:O
1144:2
1140:H
1135:2
1124:2
1120:H
1116:+
1108:2
1104:O
1095:2
1091:H
1063:2
1059:O
1050:2
1046:H
1042:+
1034:2
1030:N
1018:2
1014:H
1010:+
1003:2
968:]
960:2
956:H
952:[
946:2
941:]
935:[
929:k
926:=
923:v
900:,
897:O
889:2
885:H
880:2
877:+
869:2
865:N
853:2
849:H
844:2
841:+
834:2
782:M
779:+
776:C
770:M
767:+
722:B
719:+
716:A
674:C
667:M
657:B
654:+
651:A
598:+
587:3
566:+
555:3
525:2
523:N
521:S
502:]
499:B
496:[
491:]
488:A
485:[
478:r
474:k
467:=
461:t
458:d
453:]
449:A
445:[
442:d
416:P
410:B
407:+
404:A
337:r
333:k
308:t
274:]
271:A
266:[
241:,
237:]
233:A
229:[
223:r
219:k
212:=
206:t
203:d
197:]
193:A
189:[
185:d
133:P
105:,
102:P
96:A
34:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
