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.
A heat exchanger is a mechanical device that functions by transferring heat from one material to another through the process of conduction. The media typically involved in a heat exchange are fluids of varying temperatures. A common example of a heat exchanger is the radiator of a vehicle.