What do endothermic and exothermic mean?

Endothermic means absorbs heat. Exothermic means releases heat.

Think of it this way.

##"EX"##othermic means ##"EX"##it. If the heat is ##"EX"##iting, then it is an ##"EX"##othermic reaction.

This means that the system goes to a lower energy level.

The burning of hydrogen gas is an exothermic reaction.

##"2H"_2("g") +" O"_2("g") → "2H"_2"O"("g") + "heat"##

##"EN"##dothermic means ##"EN"##ter. If the heat is ##"EN"##tering, then it is an ##"EN"##dothermic reaction.

This means that the system goes to a higher energy level.

The decomposition of calcium carbonate into calcium oxide and carbon dioxide is an endothermic reaction.

##"CaCO"_3("s") + "heat" → "CaO"("s") + "CO"_2"(g")##

The following video shows some more exothermic and endothermic processes.