In transitive terms the difference between expand and collapse
is that
expand is to express (something) at length and/or in detail while
collapse is to cause something to collapse.
In intransitive terms the difference between expand and collapse
is that
expand is to feel generous or optimistic while
collapse is to pass out and fall to the floor or ground, as from exhaustion or other illness; to faint.
As a noun collapse is
the act of collapsing.