One crystalline form of silica (sio2) has a cubic unit cell, and from x-ray diffraction data it is known that the cell edge length is 0.700 nm. if the measured density is 2.32 g/cm3, how many

(a) si4+ and

(b) o2- ions are there per unit cell? the atomic weights of si and o are, respectively, 28.09 g/mol and 16.00 g/mol.

Apreheater involves the use of condensing steam at 100°c on the inside of a bank of tubes to heat air that enters at 1 atm and 25°c. the air moves at 5 m/s in cross flow over the tubes. each tube is 1 m long and has an outside diameter of 10 mm. what is the minimum value of nl needed to achieve an outlet temperature of t 75 c? what is the corresponding pressure drop across the tube bank?