* Heat absorbed by the system: Positive (+)
* Heat released by the system: Negative (-)
Here's a breakdown:
System: The system refers to the specific part of the universe you're studying, like a chemical reaction.
Surroundings: The surroundings are everything else outside the system.
Heat flow: Heat can flow between the system and surroundings.
Endothermic reaction: A reaction that absorbs heat from the surroundings. The system gains energy and the enthalpy change (ΔH) is positive.
Exothermic reaction: A reaction that releases heat to the surroundings. The system loses energy and the enthalpy change (ΔH) is negative.
Examples:
* Melting ice: The ice absorbs heat from the surroundings to become liquid water. This is an endothermic process, ΔH > 0.
* Burning fuel: The burning fuel releases heat to the surroundings. This is an exothermic process, ΔH < 0.
Important Note: This convention is widely accepted in chemistry, but it's crucial to check the specific context of any thermochemical calculation to confirm the convention being used.
