How can students identify exothermic and endothermic reactions?

• A. By interpreting temperature data and energy transfer.
• B. Tasting the substances to check for heat release.
• C. Only by measuring pH changes.
• D. By counting the particles in the reaction mixture.

Answer: (A)

Identifying exothermic and endothermic reactions hinges on energy transfer between the reaction and its surroundings. In an exothermic process, energy leaves the reacting system and warms the surroundings, so a thermometer shows a rise in temperature. In an endothermic process, energy enters the system, cooling the surroundings, so the temperature drops. You can measure this with a thermometer or a calorimeter to quantify heat flow. For example, burning fuel releases heat, making the surroundings hotter, while dissolving certain salts like ammonium nitrate can cool the solution. Tasting substances or judging by pH changes doesn’t reliably show energy transfer, and counting particles has nothing to do with heat energy.