Question

"To pour water on calcium oxide.” Which is another way to classify this reaction? Explain.

Answer 1

Hint The reaction of water and calcium oxide forms calcium hydroxide. There is more than one way to classify this reaction. One is based on the formation of products. The next classification is based on heat released or absorbed.

Complete step by step solution:
- Before classifying this reaction, let us first understand the reaction. When water is poured on calcium oxide - CaO (also known as quick lime), they react to form calcium hydroxide - $Ca{{(OH)}_{2}}$ (also known as slaked lime). This reaction also results in the liberation of an enormous amount of heat.
$CaO+{{H}_{2}}O\to Ca{{(OH)}_{2}}$
- So, we can see that the above reaction involves the two substances – calcium oxide and water, combining to form one product – calcium hydroxide.
- Such a reaction in which 2 or more reactants combine to form a single product is called a combination reaction.
- Hence, we can conclude that “pouring water on calcium oxide” is a combination reaction.
- Next, we have already said that the reaction involves the liberation of heat.
- Such a reaction in which, energy is released in the form of heat is called an exothermic reaction.
- Hence, we can conclude that “pouring water on calcium oxide” is an exothermic reaction.
- Combining both conclusions, we can say that “pouring water on calcium oxide” is an exothermic combination reaction.

Additional Information:
- CaO is a white crystalline solid that has many uses.
- It is used in the production of glass, organic chemicals. It is used for Also it is a key ingredient in the process of making cement. It is also used for medicinal purposes and as an ingredient in pesticides.
- $Ca{{(OH)}_{2}}$ is an inorganic white coloured crystal with a wide range of uses.
- It is used in water and sewage treatment, and also as an intermediate in the reaction for the production of NaOH.
- The above reaction- “pouring water on calcium oxide” is one we see in our daily lives. Cao, when dissolved in water during whitewashing, forms a slaked lime solution formed and this is applied on the walls and roofs of buildings. The slaked lime, then slowly reacts slowly with $C{{O}_{2}}$ in the air and this results in the formation of a shining thin layer of calcium carbonate ($CaC{{O}_{3}}$).

Note: It is important to know the difference between exothermic and endothermic reactions. The differentiating factor is heat. In an endothermic reaction, we see that heat is released as a result of the chemical reaction. On the other hand, endothermic reactions require heat for the completion of the reaction. Kindly remember this in order to avoid confusion as well as errors in identifying the type of reaction.