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.
Convective heat transfer, often referred to simply as convection, is the transfer of heat from one place to another by the movement of fluids. Convection is usually the dominant form of heat transfer in liquids and gases. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes of unknown conduction (heat diffusion) and advection (heat transfer by bulk fluid flow).