A rock containing 238U and 206Pb was examined to determine its approximate age. The sample of a rock contained 1.689g of 206Pb and 10.78g238U. Assuming no lead was originally present and that all lead formed from 238U remained in the rock, what is the age of the rock (in years)? The half-life of 238U is 4.500e+9yr. Key Concept: The age of a substance can be determined from the integrated first order rate law: In Nt/N0=kt How many kJ of energy are released to form one mole of 102Pb from protons and neutrons if the atom has a mass of 101.905634 amu? Please remember to include the mass of electrons in the calculation. Given the mass of a proton is 1.007825 amu Key Concept: The energy released from radioactive decay can be determined by determining the mass defect, m using the Einstein equation: E=mc2 How much time in years (assume a 365 day year for each year) would it take for a 1.604g sample of 60 Co to decay to a mass of 0.9154g if it has a half-life of 1.6619e+8s. Key Concept: Radioactive decay of unstable elements is a first order process and the amount of the decay can be determined by the integrated first order rate. Remember t1/2= 0.693/k