The form factors parametrizing the B-c semileptonic matrix elements can be
related to a few invariant functions if the decoupling of the spin of the h
eavy quarks in B-c and in the mesons produced in the semileptonic decays is
exploited. We compute the form factors as an overlap integral of the meson
wave functions obtained using a QCD relativistic potential model, and give
predictions for semileptonic and nonleptonic B-c decay modes. We also disc
uss possible experimental tests of the heavy quark spin symmetry in B-c dec
ays.