Which of the following is NOT a characteristic indicator that a chemical change has taken place?

Correct Option

The correct option is

Reversible change of shape

Explanation

A chemical change, or chemical reaction, involves the transformation of one or more substances into new substances with entirely different chemical properties. These changes are generally permanent and irreversible. In contrast, physical changes affect only the physical properties (such as shape, size, or state) of a substance without altering its chemical composition.

Analysis of Indicators

• Production of sound: This can be an indicator of a chemical change, such as in the explosion of fireworks or the popping sound when hydrogen gas burns.
• Change in colour: This is a common observable characteristic of chemical reactions, such as the rusting of iron or the reaction between lead nitrate and potassium iodide.
• Reversible change of shape: This is a characteristic of a physical change. For example, stretching a rubber band or molding clay changes the shape, but the chemical identity of the material remains the same. Such changes are often reversible.
• Evolution of a gas: The release of gas is a frequent indicator of a chemical reaction, such as the evolution of hydrogen gas when zinc reacts with dilute sulfuric acid.

Key Takeaway: Chemical changes are identified by indicators such as the evolution of gas, change in colour, change in temperature, or formation of a precipitate. A reversible change in physical attributes, such as shape, indicates a physical change.