# Chem 2

posted by
**Kristina**
.

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration.

a) How long will it take for 10% of the U-238 atoms in a sample of U- 238 to decay?

b)If a sample of U-238 initially contained 1.9×1018 atoms when the universe was formed 13.8 billion years ago, how many U-238 atoms will it contain today?