A reaction run in solution raises the solution's temperature from 21.0 °C to 26.4 °C. Which classification follows?

Core Concept

A rising solution temperature means the solution gained thermal energy, and that energy can only have come from the reacting system. A process that transfers heat to its surroundings is exothermic and carries a negative ΔH. Quantitatively, q for the solution comes out positive, so the reaction's q is equal and opposite in sign. The direction of the temperature change alone settles the classification; finding its size would need the solution's mass and specific heat.