Final answer:
The Ellingham diagram is standardized to show reactions with one mole of oxygen for clarity and comparison purposes. It simplifies visualization and comparison across different reactions by converting to molar terms instead of dealing with fractional molecules.
Step-by-step explanation:
In chemistry, the Ellingham diagram is typically shown for the reaction of metals with one mole of oxygen to maintain simplicity and uniformity. Since the oxygen molecule (O₂) is diatomic, using half a mole of O₂ can represent the reaction with one mole of oxygen atoms more clearly. This standardization allows for easier comparison of the thermodynamic stability of different metal oxides.
On a molecular level, it could be challenging to visualize reactions with half a molecule of oxygen, but on a molar level, it implies that we are reacting only half of a mole of oxygen molecules.
When balancing chemical equations, it is sometimes necessary to use fractional coefficients to signify the number of moles of oxygen. For instance, the calculation might show that we need to use a coefficient of (25/2) in front of O₂ to balance the reaction equation. These mole-mole calculations are important for understanding reaction stoichiometry and are fundamental in determining the proportions of reactants required.