LPG behaviour at ambient conditions When liquefied petroleum gas (LPG)—a mixture mainly of propane and butane—is released from its storage cylinder to normal atmospheric pressure and typical room temperature, what physical state and relative density characteristic should be expected?

Introduction / Context:
LPG (liquefied petroleum gas) is widely used as a domestic and industrial fuel. It is stored as a liquid under pressure, but its behaviour at normal ambient conditions determines leak dispersion, ventilation design, and safety measures. This question checks whether you know the physical state LPG assumes and whether its vapour is heavier or lighter than air when released to atmospheric pressure and typical room temperature.

Given Data / Assumptions:

• LPG is primarily a propane–butane mixture with small amounts of other light hydrocarbons.
• Conditions: approximately 1 atm and room temperature (around 20–30 °C).
• We are concerned with the state of the released LPG and its density relative to air.

Concept / Approach:
Under pressure, LPG is a liquid. When the valve is opened and the pressure drops to atmospheric, part of the liquid flashes to vapour and chills the remaining liquid. At ordinary ambient temperatures above the boiling points of propane and butane at 1 atm, LPG does not remain a bulk liquid; it becomes a gas. The molecular weights of propane (~44) and n-butane (~58) exceed the average molecular weight of air (~29), so LPG vapour is denser than air and tends to settle in low spots unless dispersed.

Step-by-Step Solution:

Verification / Alternative check:
MSDS sheets and safety codes note that LPG vapours accumulate at floor level, confirming heavier-than-air characteristics, and that LPG is stored as a liquid only under pressure or at low temperature.

Why Other Options Are Wrong:

• Gas lighter than air: Incorrect; propane/butane vapours are denser than air.
• Liquid lighter/heavier than water: Not applicable at 1 atm and room temperature; LPG does not remain a bulk liquid.

Common Pitfalls:
Assuming “gas cylinder” implies a gas remains liquid after release; it only stays liquid while pressurised or cold.

Final Answer:
Gas heavier than air