Actually, some isotopes can change the rate of a reaction- these effects are best observed are the lighter elements such as deuterium or tritium (2x or 3x the mass of hydrogen) although the kinetic isotope effect is observed with carbon 13 compared to carbon 12 as well. Heavy elements don't show enough of a mass difference to show the kinetic isotope effect well

For general information, please see:

http://en.wikipedia.org/wiki/Kinetic_isotope_effect

http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/06._One_Dimensional_Harmonic_Oscillator/Kinetic_Isotope_Effects

Some examples here: https://www.princeton.edu/chemistry/macmillan/group-meetings/RRK-KIE.pdf

Dear Pervaiz

As per my opinion, the changing the isotopes, there will be no change in chemical properties. because it depended on electronic configuration and mostly on outer electrons.

Isotops dont change the chemical behavior of a material. Just physical properties like mass, neutron scattering and so on are affected.

Actually, some isotopes can change the rate of a reaction- these effects are best observed are the lighter elements such as deuterium or tritium (2x or 3x the mass of hydrogen) although the kinetic isotope effect is observed with carbon 13 compared to carbon 12 as well. Heavy elements don't show enough of a mass difference to show the kinetic isotope effect well

For general information, please see:

http://en.wikipedia.org/wiki/Kinetic_isotope_effect

http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/06._One_Dimensional_Harmonic_Oscillator/Kinetic_Isotope_Effects

Some examples here: https://www.princeton.edu/chemistry/macmillan/group-meetings/RRK-KIE.pdf

Jack Silver is right.  Especially for hydrogen isotopes, reaction rates can vary significantly.  Other examples for hydrogen isotopes: the HD, HT and DT diatomic molecules have electric dipole moments, unlike H_2, and their specific heats are quite different; there is a large isotope effect in dissociative attachment; the HD+ H chemical reactions have much different rates at low temperature, etc. There is a vast literature on carbon-12/carbon-13 ratios in biomaterial - for example, this ratio differs between orange juices produced in different places - and this reflects slight differences in the effective rates of biochemical processes.

The chemical properties of D2O can be quite different too. 

I would think that the biggest difference between isotopes would occur if you change out a stable isotope for a radioactive isotope or a more stable for a less stable isotope. 

Yes, it certainly changes but changes are difficult to measure, it is very very few but very usefull if you can measure it. Two main mechanisms:

1) mass effect on the vibrating energy of a bond. The larger is the mass difference, the greater is the effect. The stongest effect is detected on H and D.

2) Nuclear spin - single electron spin coupling, for example, It is used to track possible reaction scheme with mercury to detect if single electron (radicals) are involved.

There are isotope effects in spectroscopy, chemical equilibrium, phase equilibrium, physiochemical properties, reaction kinetics and biology.

http://www.google.ro/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&cad=rja&uact=8&ved=0CCIQFjABOAo&url=http%3A%2F%2Fwww.eolss.net%2Fsample-chapters%2Fc06%2Fe6-104-01-00.pdf&ei=bod1VJedBMLB7AaIhoGQBA&usg=AFQjCNFolv6H4Sq8VeRz3z9jtyUuCpClZg