  To investigate the impact of matter mixing on the formation of molecules in
the ejecta of SN 1987A, time-dependent rate equations for chemical reactions
are solved for one-zone and one-dimensional ejecta models of SN 1987A. The
latter models are based on the one-dimensional profiles obtained by
angle-averaging of the three-dimensional hydrodynamical models (Ono et al.
2020), which effectively reflect the 3D matter mixing; the impact is
demonstrated, for the first time, based on three-dimensional hydrodynamical
models. The distributions of initial seed atoms and radioactive $^{56}$Ni
influenced by the mixing could affect the formation of molecules. By comparing
the calculations for spherical cases and for several specified directions in
the bipolar-like explosions in the three-dimensional hydrodynamical models, the
impact is discussed. The decay of $^{56}$Ni, practically $^{56}$Co at later
phases, could heat the gas and delay the molecule formation. Additionally,
Compton electrons produced by the decay could ionize atoms and molecules and
could destruct molecules. Several chemical reactions involved with ions such as
H$^+$ and He$^+$ could also destruct molecules. The mixing of $^{56}$Ni plays a
non-negligible role in both the formation and destruction of molecules through
the processes above. The destructive processes of carbon monoxide and silicon
monoxide due to the decay of $^{56}$Ni generally reduce the amounts. However,
if the molecule formation is sufficiently delayed under a certain condition,
the decay of $^{56}$Ni could locally increase the amounts through a sequence of
reactions.
