Question

What is the type of the following chemical reaction?
\[CaC{{O}_{3}}\to CaO+C{{O}_{2}}\]

A. Combination
B. Displacement
C. Decomposition
D. Synthesis

Answer 1

Hint: Think about the definitions of all the options that are given, think about them as words and not the type of reaction that they represent. This will give you an intuitive sense of what will happen in each reaction type and help you classify the given reaction.

Complete step by step answer:
We will first look at the meanings of each of the words given in the options and the type of reactions they represent before classifying the given reaction.

- Combination
The word itself means that two or more given components will combine to form a new component. The reactants will combine and produce only one product. It will involve the direct combining of two reactant molecules without the loss of any atoms that were originally present within them. The general reaction is: \[X+Y\to X-Y\]

- Displacement
This indicates the replacement of one component by another component. In displacement reactions, one ion replaces another similar ion and forms a more stable or favourable molecule. Double displacement reaction is a more complex reaction that involves the displacement of ions on two different atoms. The general reaction is: \[A+B-C\to A-C+B\]
Here, $A$ is considered to be more reactive than $B$.

- Decomposition
When something is said to be decomposing, it refers to the breakdown of that material on a molecular level. A decomposition reaction involves the breakdown of one molecule into 2 or more parts which are relatively stable and will not immediately combine to form the original molecule. The general reaction is:
\[X-Y\to X+Y\]

- Synthesis
To synthesize is to make something. This is another name for a combination reaction but the information that we have beforehand will be different. This term is usually used when the end product is known and we are looking at the reactions that give that particular molecule as one of its products. Synthesis reactions are usually combination reactions but can also be redox reactions. The general reaction is:
\[A+B\to A-B\]

In the given reaction, we can see that a molecule of calcium carbonate breaks down into a molecule of calcium oxide and carbon dioxide. There is only one reactant present but two products are present. So, we can say that the calcium carbonate is decomposing and this is a decomposition reaction.
So, the correct answer is “Option C”.

Note: Decomposition reactions are usually not referred to as synthesis reactions. This happens as we usually do not tend to go for the breakdown of a complex molecule to get our desired molecule. In the given example, if we were looking to synthesize a calcium oxide molecule, we will look for reactions where calcium and oxygen combine, not reactions where complex molecules like calcium carbonate or calcium sulphite are broken down.