Isotope effects refer to the changes in the chemical or physical properties of a substance that occur due to the differences in the mass of the isotopes of atoms within that substance. These effects can manifest in various ways, such as altered reaction rates, equilibrium constants, bond strengths, and vibrational frequencies. Isotope effects are often used in research to investigate reaction mechanisms, study biological processes, and understand geological and environmental processes. They play a significant role in fields such as chemistry, biochemistry, geology, and environmental science.