Final answer:
The equation Hf H2O(l) = -286 kJ represents the enthalpy change when 1 mole of liquid water is formed from its elements, hydrogen gas (H₂) and oxygen gas (O₂). It releases 286 kJ of heat to the surroundings, indicating the thermodynamic stability of liquid water.
Step-by-step explanation:
The equation Hf H2O(l) = -286 kJ represents the enthalpy change when 1 mole of liquid water is formed from its elements, hydrogen gas (H₂) and oxygen gas (O₂), at the same temperature and pressure. The negative value of -286 kJ indicates that this process releases 286 kJ of heat to the surroundings. The equation can be written as:
H₂(g) + 1/2 O₂(g) → H₂O(l)
This equation demonstrates that the formation of liquid water is an exothermic reaction, meaning it releases heat energy. The stability of liquid water can be inferred from the enthalpy change being negative, suggesting that the water molecule is thermodynamically stable.