Timing, exact rates and weather conditions are extremely important. A good option is to hire a professional lawn care specialist to apply chemicals. Spot spraying with a selective broadleaf herbicide (weed killer for lawns) is a good way to kill your weeds without damaging your lawn. I spot spray (as opposed to applying herbicides to the entire lawn) most of the lawns that I manage because it uses less chemicals and is the responsible approach to take.
Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole. If one end of a metal rod is at a higher temperature, then energy will be transferred down the rod toward the colder end because the higher speed particles will collide with the slower ones with a net transfer of energy to the slower ones.
The last method heat transfer would be convection. This is the transfer of heat through fluid or air currents. As something heats up, the particles will spread out and thus become less dense. An example of convection would be a pot of water starting to boil on a stove.