Q61
General ScienceChemistry
$Mg(s) + O_2(g) \rightarrow MgO(s) + \text{energy}$, this reaction may be classified as a/an
- a.Combination reaction
- b.Oxidation reaction
- c.Exothermic reaction
- d.All of the above
Answer: (D) All of the above
The balanced equation is $2Mg + O_2 \rightarrow 2MgO$ (the equation printed in the paper is unbalanced). Two substances join to give a single product, so it is a combination reaction. Magnesium gains oxygen and loses electrons (0 to +2), so it is an oxidation — strictly a redox reaction, since oxygen is reduced. Heat and a dazzling white light are given out, so it is exothermic. Hence all three descriptions apply. The white ash, magnesium oxide, is a basic oxide; dissolved in water it forms $Mg(OH)_2$, which turns red litmus blue.