1. The problem statement, all variables and given/known data Estimate the lifetime of a proton against fusion to 4He in the center of a Zero-Age-Main-Sequence solar mass star. First calculate the energy generation, εpp in the center of the star from the p-p chain. Then convert this to the number of fusions (conversion of 4 protons to 1 4He) per unit volume per second. Finally compare this rate to the central number density of protons to estimate the lifetime. Constants: (C = stellar core values) TC = 13*106 K ρC = 78 g/cm3 XH (Mass fraction Hydrogen) = 0.7 2. Relevant equations εpp ~ 1.07*10-6*(ρC)*(XH)2*(T6)4 3. The attempt at a solution This was an exam problem - I know how to find the energy generation rate as well as the number density of protons. Neither are difficult. I do not, however, have any idea how to convert the energy generated in to the number of fusions per volume per second. If anyone has a first step, that's really all I'm looking for but I genuinely have no idea how to even begin. I was thinking it might involve going through the PP-I -> PP-IV branches individually but that seems far too complicated.