How do changes in odour indicate chemical changes?

Changes in odour indicate chemical changes as they suggest new substances with different properties have been formed.

In chemistry, a chemical change refers to a process where one or more substances are transformed into different substances. These new substances have different physical and chemical properties, including different odours. When a chemical reaction occurs, the bonds between atoms in the reactants are broken and new bonds are formed to create the products. This process often results in the formation of new substances with different properties, including different smells.

For example, when hydrogen sulphide gas (which has a rotten egg smell) reacts with oxygen, it forms water and sulphur dioxide, which has a different, pungent smell. This change in odour is a clear indication that a chemical change has occurred. Similarly, when a piece of bread is toasted, the heat causes a chemical reaction that changes the composition of the bread, producing a new, toasted smell.

Another example is the process of fermentation. In this process, yeast consumes sugar and produces alcohol and carbon dioxide. The smell of the dough changes as the sugar is converted into alcohol, indicating a chemical change.

In some cases, the change in odour can be quite dramatic and easily noticeable, such as when food spoils. The bacteria and fungi responsible for food spoilage break down the food's components, producing gases with unpleasant smells. This is a clear sign of a chemical change.

In conclusion, changes in odour are a useful indicator of chemical changes. They provide a sensory clue that the composition of a substance has changed, and new substances with different properties have been formed. This is a fundamental concept in chemistry, and understanding it can help you to identify when chemical reactions have occurred.