Two different liquids are mixed together. which observation indicates that an exothermic chemical reaction has taken place?

Well for one, A LOT of heat (or if you wanna call it energy) is being released from the mixture and the container itself starts to heat up and you can DEFINITELY feel the heat. EXO: Outside, exterior. THERMIC: Heat, something to describe hot stuff (I guess).

SO you can say it heats up the outside container and occasionally will produce steam or foam (DEPENDING ON WHAT YOU MIX)

Because a model would make the investigation easier to understand

The correct answer is "atomic weight".