Does a temperature change always indicate that a chemical reaction has occurred?

if you are trying to react 2 things that are near the same temperature, the answer is yes (i.e. HCl and Na2CO3 at room temperature gives off heat).

if you are reacting things at very different temperatures, then no. for example, a temperature change occurs when you put ice in your soda, or if you try to react Xe at room temp with liquid nitrogen (the Xe will be cooled greatly and the N2 will warm, but there will be no reaction)

so i would say no

NO!!!! There is transfer of heat involved with many processes that have nothing to do with chemical reactions. If for example, sodium hydroxide at room temperature is dissolved in water at room temperature, the solution becomes so hot it is close to boiling. No chemical reaction has taken place, just one chemical dissolving in another. The warning to add acid to water instead of water to acid is done for the same reason - so much heat is generated so fast by the mixing that the water might explosively vaporize and splash acid on whoever is nearby.

For the opposite effect, dissolving urea in water at room temperature will cause the solution to become very cold - this is the basis for instant cold packs.