The rate constant for a second-order reaction is 0.13 m-1 sec-1. if the initial concentration of reactant is 0.26 mol/l, it takes sec for the concentration to decrease to 0.13 mol/l.

The number  of seconds for  the concentration  to decrease  to  0.13 mol  for a second  order  reaction is  calculated  using  the below  formula

1/At  =-Kt  +1/Ao  where  At   is  the final concentration, Ao  is the   initial concentration.  t = time in second   while k =  constant

1/0.13 =-0.13 (t) + 1/0.26
like terms together

1/0.13-1/0.26 =-0.13 t
divide both side by 0.13

T =29.6 seconds

This is a solution, hope i could

Vander waals forces are inter molecular bonds that exist within molecules of the same substance. a water molecule is made up of oxygen and hydrogen atoms which share electrons between each other. the vander waals forces are forces that exist between multitude of different  molecules of water. dipole dipole forces is the type of vander waals force that exist in water. the oxygen atom which is more electronegative pulls the shared electron closer to itself thus generating a partial negative charge while the hydrogen acquire a partial positive charge. these two different charges causes attraction to occur in water molecules.