Understanding the Concepts
* Exothermic Reaction: A reaction that releases heat into the surroundings. This means the enthalpy change (ΔH) for the reaction is negative.
* Formation of a Compound: This refers to the process of combining elements to create a new compound.
* Standard Conditions: 298 K (25°C) and 101.3 kPa (1 atm) are considered standard conditions for chemical reactions.
Identifying the Compound
The most common example of an exothermic reaction at standard conditions is the formation of water (H₂O) from its elements, hydrogen (H₂) and oxygen (O₂):
2H₂(g) + O₂(g) → 2H₂O(l) ΔH = -571.6 kJ/mol
Explanation
The formation of water from its elements is highly exothermic. The strong bonds formed in the water molecule release a significant amount of energy, making the reaction favorable.
Important Note: There are other exothermic reactions that form compounds under standard conditions. However, the formation of water is a classic and well-known example.
