A student writes the equation: Mg + O₂ → MgO. Is this a complete and balanced chemical equation? State two wa…

Question

A student writes the equation: Mg + O₂ → MgO. Is this a complete and balanced chemical equation? State two ways in which it is incomplete or incorrect.

Accepted Answer

## Model Answer No, it is **not** a complete and balanced chemical equation. It is only a **skeletal chemical equation**. Two ways it is incomplete/incorrect: 1. **Unbalanced:** LHS has 2 oxygen atoms (O₂) but RHS has only 1 (MgO), violating the law of conservation of mass. 2. **Physical states missing:** The symbols (s), (g), etc., for reactants and products are not mentioned, making the equation incomplete. *Source: Chapter 1, Sections 1.1.1 and 1.1.2* --- ## Explanation Examiners look for two distinct points: (1) the balancing issue — atoms of Mg and O are unequal on both sides, and (2) the missing physical state symbols (s/g/l/aq). The textbook explicitly calls Mg + O₂ → MgO a "skeletal chemical equation." A balanced form would be **2Mg + O₂ → 2MgO**. Always name both errors clearly for full marks.

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