Volatile liquids usually

Analysis

The question asks for the defining physical characteristic of "volatile liquids." To answer this, we need to understand what volatility means in the context of thermodynamics and molecular physics.

Concept Explanation

Volatility refers to the tendency of a substance to vaporize or turn into a gas at a given temperature.

• A substance is considered "volatile" if it evaporates easily at room temperature.
• Evaporation occurs when molecules at the surface of a liquid have enough kinetic energy to overcome the intermolecular forces holding them in the liquid state.
• Liquids that evaporate easily have weak intermolecular forces. Because these forces are weak, it does not take much heat energy to break them, which results in a low boiling point.

Step-by-Step Solution

1. Define Volatility: Volatility is the measure of how easily a liquid turns into vapor.
2. Relate to Boiling Point: The boiling point is the temperature at which the vapor pressure of a liquid equals the external atmospheric pressure.
3. Analyze the Relationship: If a liquid is highly volatile, it exerts a high vapor pressure even at low temperatures. Therefore, it reaches the boiling point much faster (at a lower temperature) than a non-volatile liquid.
4. Evaluate Options: • A: Incorrect. High boiling points indicate strong intermolecular forces, which make a liquid stable and less likely to evaporate. • B: Correct. Low boiling points mean the liquid requires very little heat to transition into a gas, which is the definition of volatility. • C: Incorrect. Density is the mass per unit volume and is not directly related to the volatility of a liquid. • D: Incorrect. Melting point relates to the transition from solid to liquid, not liquid to gas.

Conclusion

Volatile liquids, such as petrol or methylated spirit, have weak intermolecular forces, which allow them to vaporize readily at low temperatures. This corresponds to having a low boiling point.

Exam Tip: Think of "volatile" as "flighty" or "quick to leave." If a liquid is quick to leave the liquid state and become a gas, it must have a low boiling point. This is a common JAMB question, so remember: High Volatility = Low Boiling Point.