Would the atomic mass be different if you received another bag of pennies containing a different mixture of pre-1982 and post-1982 pennies?

Yes, the Atomic Mass would differ if you received another bag of pennies with a different mixture of pre-1982 and post-1982 pennies, as these two types have different compositions. Pre-1982 pennies are made primarily of copper, while post-1982 pennies are mostly zinc with a thin copper coating. This variation in material composition affects the overall mass of the pennies in the bag, resulting in a different average atomic mass.