A substance decomposes upon heating. Choose the appropriate classification from the response list below:
a) could be an element or a compound
b) could be an element but not a compound
c) could be a compound but not an element
d) could not be an element nor a compound
The correct answer and explanation is :
The correct answer is:
c) could be a compound but not an element
Explanation:
When a substance decomposes upon heating, it breaks down into two or more simpler substances. This behavior is a defining characteristic of compounds, not elements.
Elements are pure substances made of only one type of atom. They are the simplest form of matter and cannot be broken down into simpler substances by chemical or physical means, including heating. Examples include oxygen (O₂), gold (Au), and iron (Fe). Even if you heat gold or oxygen, they won’t decompose into anything simpler — they will remain elements or undergo phase changes (like melting or vaporizing) without breaking into new substances.
Compounds, on the other hand, consist of two or more different types of atoms chemically bonded together. These bonds can be broken by the input of energy, such as heat, causing the compound to decompose into its constituent elements or simpler compounds. A common example is calcium carbonate (CaCO₃). When heated, calcium carbonate decomposes into calcium oxide (CaO) and carbon dioxide (CO₂) gas:
[
\text{CaCO}_3 \xrightarrow{\Delta} \text{CaO} + \text{CO}_2
]
Since decomposition is a chemical change that splits a substance into simpler substances, and only compounds are made of multiple elements chemically combined, only a compound can decompose in this way.
Thus, if a substance decomposes upon heating, it cannot be an element because elements are already in their simplest chemical form. It must therefore be a compound.
Summary:
- Elements: Cannot decompose by heating.
- Compounds: Can decompose by heating into simpler substances.
- Correct choice: c) could be a compound but not an element.