Respuesta :
Answer:
Explanation:
There is no way to measure the absolute value of the enthalpy of a substance. Only values relative to an arbitrary reference can be determined.
The reference point for all enthalpy expressions is called the standard enthalpy of formation (ΔHºf). Substances are said to be in the standard state at 1 atm, hence the term “standard enthalpy.” The superscript “°” represents standard-state conditions (1 atm), and the subscript “f” stands for formation. By convention, the standard enthalpy of formation of any element in its most stable form is zero.
For instance, molecular oxygen (O₂) is more stable than the other allotropic form of oxygen, ozone (O₃), at 1 atm and 25°C. Thus, we can write ΔHºf (O₂) 5 0, but ΔHºf (O₃) 5 142.2 kJ/mol.
Based on this reference for elements, we can define the standard enthalpy of formation of a compound as the heat change that results when 1 mole of the compound is formed from its elements at a pressure of 1 atm.
Answer:
This is the enthalpy change that occurs when a compound is formed from its component elements.
Explanation:
This is the enthalpy change that occurs when a compound is formed from its component elements.
