The average atomic mass of lithium is 6.94 amu. Based on the atomic masses of the two isotopes of lithium, how do the relative abundances of the
isotopes compare?
Isotope
Atomic mass (amu)
Li-6
6.015
Li-7
7.016
A. Li-7 is slightly more abundant than Li-6.
B. They are about the same.
C. Li-6 is much more abundant than Li-7.
D. LI-7 is much more abundant than Li-6

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.