A spherical naphthalene ball with an initial diameter of 1.2 cm slowly sublimes in a large volume of still air at 15°C and 1 atm. At this temperature, the sublimation pressure of naphthalene is 0.036 mmHg.

Assuming pseudo-steady-state and neglecting convection, determine: 

(a) The initial, pseudo-steady-state rate of sublimation expressed as a percentage of the mass of the ball sublimed per day.

(b) The time required to reduce the naphthalene ball diameter to one-tenth of the initial value.

Note that the rate of sublimation will change over time. Thus, the mass balance equation for the naphthalene ball needs to be integrated to determine the correct time.