Let us consider the simple reaction: A+B→kY MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8akY=wiFfYdH8Gipec8Eeeu0xXdbba9frFj0=OqFfea0dXdd9vqai=hGuQ8kuc9pgc9s8qqaq=dirpe0xb9q8qiLsFr0=vr0=vr0dc8meaabaqaciaacaGaaeqabaqabeGadaaakeaacqqGbbqqcqGHRaWkcqqGcbGqdaGdKaWcbaGaem4AaSgabeGccaGLsgcacqqGzbqwaaa@33D2@ occurring in a finite volume V. To first order, the rate of change in the number of molecules Y is: