In combustion of a spherical coal particle in the air, O2 in the air diffuses to the particle surface and the generated CO2 diffuses from the particle surface. The particle has an initial diameter of 6.7cm and diffusivity of O2 in the air is 0.2cm/s at 25C and latm. Assume that the combustion reaction of carbon with O2 is very fast, and the coal particle is made of carbon, and that other components are negligible. The density of coal is 1.5 x 10kg/m3 Determine (make necessary assumptions if needed) 1. the flux of CO2 from the surface of charcoal particle; 2. how particle diameter varies with time; 3. how long it takes for the coal particle to completely disappear