Explain why a mixture of zinc oxide and magnesium reacts when heated while there is no reaction when a mixture of zinc and magnesium oxide is heated

Magnesium is a more active metal than zinc. That is, Mg will undergo oxidation (loss of electrons) more readily than Zn which in ZnO would gain the electrons donated by Mg. The MgO bond is more stable than the ZnO bond which resists replacement by less active metals such as Zn. A review of 'The Activity Series' of reactive metals and 'Single Replacement Reactions, is suggested.

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Magnesium is more reactive than zinc hence when Mg is reacted with ZnO, it is oxidised while ZnO is reduced to Zn this the name redox reaction. When MgO is reacted with Zn nothing happens since Mg is more reactive than Zn and Zn cannot be oxidised while MgO cannot be reduced to Mg

When trying to understand why a specific reaction occurs or doesn't occur, it is essential to consider the chemical properties and behaviors of the compounds involved. In this case, we are evaluating the reactions between zinc oxide and magnesium, as well as between zinc and magnesium oxide.

1. Zinc Oxide and Magnesium Reaction:
When a mixture of zinc oxide (ZnO) and magnesium (Mg) is heated, a reaction takes place. This reaction can be explained by the electrochemical series, which ranks elements based on their tendencies to lose or gain electrons.

In this reaction, zinc oxide acts as an ionic compound, where zinc is a cation (+2 charge) and oxygen is an anion (-2 charge). On the other hand, magnesium is a metallic element that readily loses its two valence electrons, resulting in a +2 cationic charge.

When heated, the high temperature provides the necessary energy for the reactions to occur. The exothermic reaction takes place when zinc and magnesium ions displace each other. The zinc ion from zinc oxide combines with two electrons from magnesium, forming metallic zinc (Zn) and leaving magnesium oxide (MgO) behind. Simultaneously, the magnesium ion from magnesium combines with oxygen from the zinc oxide, producing magnesium oxide.

2. Zinc and Magnesium Oxide Reaction:
Conversely, when a mixture of zinc and magnesium oxide (Zn + MgO) is heated, no reaction occurs. This lack of reaction can be explained by the relative positions of zinc and magnesium in the electrochemical series.

Zinc, being higher in the electrochemical series, has a greater tendency to lose electrons compared to magnesium. Therefore, zinc is more reactive than magnesium. When heated with magnesium oxide, zinc cannot displace magnesium from the oxide. This is because magnesium is lower in the electrochemical series than zinc, making it less likely for it to lose electrons and undergo a reaction. As a result, no reaction occurs between zinc and magnesium oxide.

In summary, the reaction between zinc oxide and magnesium occurs because of the different electrochemical properties of the two compounds. On the other hand, the lack of reaction between zinc and magnesium oxide is due to their positions in the electrochemical series, where zinc is more reactive than magnesium.