Question

Burning magnesium ribbon in air to form magnesium oxide is an example of ______ reaction.

Answer 1

Hint: In the given question, focus on the word burning. Burning a reactant signifies that energy will be released from the provided to a system.

Complete step by step answer:
As we can see from the question, magnesium ribbon burns in air to form magnesium oxide. The reaction can be written as –
$2Mg(s)+{{O}_{2}}(g)\to 2MgO(s)+energy$
The reaction, along with a white coloured solid (magnesium Oxide – MgO), also releases heat and light.
The burning (oxidation or combustion) of magnesium in air has long been used as a source of intense light in photography and for other photochemical reactions. The heat of formation of magnesium oxide is around - 601.83 kJ/mol. When magnesium burns, approximately 10 $\%$ of the combustion energy is released as light.
Since energy is released, the heat of enthalpy will be negative. Therefore, we can say that this is an example of an exothermic reaction.
Therefore, the answer is – burning magnesium ribbon in air to form magnesium oxide is an example of exothermic reaction.

Additional information:
In this reaction, magnesium gives up two electrons to oxygen atoms to form magnesium oxide. Along with exothermic, this reaction is also an example of combination reaction.

Note: Magnesium ribbon should be necessarily cleaned before burning it in air in order to remove the protective layer of basic magnesium carbonate from its surface.