  [Abridged] Planets and their atmospheres are built from gas and solid
material in protoplanetary disks. This solid material grows from smaller,
micron-sized grains to larger sizes in the disks, during the process of planet
formation. Our goal is to model the compositional evolution of volatile ices on
grains of different sizes, assuming both time-dependent grain growth and
several constant grain sizes. The state-of-the-art Walsh chemical kinetics code
is utilised for modeling chemical evolution. This code has been upgraded to
account for the time-evolving sizes of solids. Chemical evolution is modelled
locally at four different radii in a protoplanetary disk midplane for up to
10Myr. The evolution is modelled for five different constant grain sizes, and
one model where the grain size changes with time according to a grain growth
model appropriate for the disk midplane. Local grain growth, with conservation
of total grain mass and the assumption of spherical grains, acts to reduced the
total grain-surface area that is available for ice-phase reactions. This
reduces these reactions efficiency compared to a chemical scenario with a
conventional grain-size choice of 0.1$\mu$m. The modelled chemical evolution
with grain growth leads to increased abundances of H$_{2}$O ice. For carbon in
the inner disk, grain growth leads CO gas to overtake CO$_{2}$ ice as dominant
carrier, and in the outer disk, CH$_{4}$ ice to become the dominant carrier.
Overall, a constant grain size adopted from a grain evolution model leads to
almost identical chemical evolution, when compared with chemical evolution with
evolving grain sizes. A constant grain size choice, albeit larger than
0.1$\mu$m, may therefore be an appropriate simplification when approximating
the impact of grain growth on chemical evolution.
