Calcium oxide reacts with water to produce slaked lime. It is an examp

Calcium oxide reacts with water to produce slaked lime. It is an example of

combination reaction
decomposition reaction
oxidation reaction
addition reaction
This question was previously asked in
UPSC CAPF – 2022
The reaction described is between calcium oxide ($\text{CaO}$) and water ($\text{H}_2\text{O}$) to produce slaked lime, which is calcium hydroxide ($\text{Ca(OH)}_2$).
The balanced chemical equation for this reaction is:
$\text{CaO(s)} + \text{H}_2\text{O(l)} \rightarrow \text{Ca(OH)}_2\text{(aq)}$

Let’s analyze the types of reactions given in the options:
A) Combination reaction: A reaction in which two or more reactants combine to form a single product. In this reaction, calcium oxide and water (two reactants) combine to form calcium hydroxide (a single product). This matches the definition of a combination reaction.
B) Decomposition reaction: A reaction in which a single compound breaks down into two or more simpler substances. This is the opposite of the given reaction.
C) Oxidation reaction: A reaction involving the loss of electrons or increase in oxidation state. While redox aspects might be present in the formation of bonds, the primary classification based on the change in the number of substances is combination. The oxidation states of Ca (+2), O (-2), and H (+1) do not change overall.
D) Addition reaction: A reaction in which atoms are added to a molecule across a multiple bond (like a double or triple bond). This term is mainly used in organic chemistry for reactions involving unsaturated hydrocarbons. While water is added to CaO, the term ‘combination reaction’ is the standard classification for this type of inorganic reaction.

The reaction fits perfectly the definition of a combination reaction. It is also a highly exothermic reaction, releasing a significant amount of heat, which is why it is also called the slaking of lime.

– Identifying the reactants and products of the reaction: Calcium oxide + Water -> Calcium hydroxide.
– Understanding the definition of different types of chemical reactions.
– Classifying the reaction based on the change in the number of reactants and products. Two reactants form one product, characteristic of a combination reaction.
This reaction is a classic example of an inorganic combination reaction and the process of slaking quicklime ($\text{CaO}$) to produce slaked lime ($\text{Ca(OH)}_2$). Slaked lime has many uses, including in mortars, plasters, and water treatment. The reaction is also an example of a hydrolysis reaction because water is a reactant. However, among the given choices, “combination reaction” is the most appropriate primary classification.
Exit mobile version