The effect on the rate or equilibrium constant of two reactions that differ only in the isotopic composition of one or more of their otherwise chemically identical components is referred to as a kinetic isotope effect or a thermodynamic (or equilibrium) isotope effect, respectively.
Sources:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1130 (https://doi.org/10.1351/pac199466051077)
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2521 (https://doi.org/10.1351/pac199466122513)
See also:
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 170 (https://doi.org/10.1351/pac199668010149)