2.19 for a k+−cl− ion pair, attractive and repulsive energies ea and er, respectively, depend on the distance between the ions r, according to e a = − 1.436 r e r = 5.86 × 10 − 6 r 9 ea=−1.436rer=5.86×10−6r9 for these expressions, energies are expressed in electron volts per k+−cl− pair, and r is the distance in nanometers. the net energy en is just the sum of the preceding two expressions. (a) superimpose on a single plot en, er, and ea versus r up to 1.0 nm. (b) on the basis of this plot, determine (i) the equilibrium spacing r0 between the k+ and cl− ions, and (ii) the magnitude of the bonding energy e0 between the two ions.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?