What are the signs of heat quantity in exothermic and endothermic reaction and why those signs

Exothermic reactions: The sign of the heat quantity is negative ($q < 0$ or $\Delta H < 0$).

• Why: Exothermic reactions release heat energy to the surroundings. This means the system (the reacting chemicals) loses energy. By convention, when a system loses energy in the form of heat, the heat quantity is assigned a negative sign.

Endothermic reactions: The sign of the heat quantity is positive ($q > 0$ or $\Delta H > 0$).

• Why: Endothermic reactions absorb heat energy from the surroundings. This means the system (the reacting chemicals) gains energy. By convention, when a system gains energy in the form of heat, the heat quantity is assigned a positive sign.