In which equation does the term "heat" represent heat of fusion?
(1) nacl(s) + heat --> nacl(l)
(2) naoh(aq) + hcl(aq) --> nacl(aq) + h2o(l) + heat
(3) h2o(l) + heat --> h2o(g)
(4) h2o(l) + hcl(g) --> h3o+(aq) + cl-(aq) + heat