Chem 2/5 Labs FS/98 Postlab-Radioactivity #468 (1) An element has a rate constant (K) of 3.45 x 10-3 sec-1 (a) What is the half life for the element ? (b) If we started with 100g of the element, how much would we have left after 700 seconds (2) What is X in the following reactions ? 214 210 Po ---> Pb + X 84 82 238 4 U ---> X + He 92 2