1. The problem statement, all variables and given/known data Take an elastic balloon of volume V in vacuum. The surface of the balloon has tension T. Find the pressure inside the balloon in terms of V and T, then combine this to the ideal gas law to find an expression for V. 2. Relevant equations See below 3. The attempt at a solution I think one should use something like dU=-pdV, but you need to add a term with T. From dimensional analysis you get TdA. So you have dU=-pdV+TdA. But I'm confused on what happens then, I get something like p=-(dU/dV)+T(dA/dV) But then how does this help if I want V?