The partial charges on a water molecule occur because of

The partial charges on a water molecule occur because of  the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule.

Water molecule has partial charges since the electrons shared are closer to the oxygen than the hydrogen. This means that each water molecule has a partial positive charge on the hydrogens and a partial negative charge on the oxygen.

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.