1. The problem statement, all variables and given/known data A (spherical) rubbery balloon of 20 cm in diameter is filed with helium. The rubber balloon wall has a thickness of 0.05 cm and diffusivity of 0.1x10-10 cm2 /s for helium. When the balloon is left in the air at 25°C, helium leaks into the air by diffusion through the rubbery wall and, as a result, the balloon shrinks. The Henry constant for helium in the rubber is 5 mol/cm3 .atm. (1) Derive an equation that correlates the balloon size to the time; (2) Estimate the time required for the balloon to shrink to 10 cm in diameter. (Note: The helium pressure in the balloon is 2 atm and is essentially constant during the shrinking process. To simplify calculation, a quasi steady state can be assumed for the problem). 2. Relevant equations J = (DH/L)(Ca - Cb) Q = J.A.Δt d(v(P/RT))/dt = -SJ 3. The attempt at a solution I am having trouble starting this problem. I think that I need to somehow incorporate the mass balance with the flux equation. Then I get confused as to how I would derive the equation to equate the the balloon size as a function of time. Does my though process sound like I am on the right track? Thank you in advance for any help!