  While the importance of supernova feedback in galaxies is well established,
its role on the scale of molecular clouds is still debated. In this work, we
focus on the impact of supernovae on individual clouds, using a high-resolution
magneto-hydrodynamic simulation of a region of 250 pc where we resolve the
formation of individual massive stars. The supernova feedback is implemented
with real supernovae that are the natural evolution of the resolved massive
stars, so their position and timing are self-consistent. We select a large
sample of molecular clouds from the simulation to investigate the supernova
energy injection and the resulting properties of molecular clouds. We find that
molecular clouds have a lifetime of a few dynamical times, less then half of
them contract to the point of becoming gravitationally bound, and the dispersal
time of bound clouds, of order one dynamical time, is a factor of two shorter
than that of unbound clouds. We stress the importance of internal supernovae,
that is massive stars that explode inside their parent cloud, in setting the
cloud dispersal time, and their huge overdensity compared to models where the
supernovae are randomly distributed. We also quantify the energy injection
efficiency of supernovae as a function of supernova distance to the clouds. We
conclude that intermittent driving by supernovae can maintain molecular-cloud
turbulence and may be the main process of cloud dispersal. The role of
supernovae in the evolution of molecular clouds cannot be fully accounted for
without a self-consistent implementation of their feedback.
