Problem 24 - Chemistry and Chemical Reactivity

Question

Methane \(\left(\mathrm{CH}_{4}\right)\) cannot be liquefied at room temperature, no matter how high the pressure. Propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),\) another simple hydrocarbon, has a critical pressure of 42 atm and a critical temperature of \(96.7^{\circ} \mathrm{C} .\) Can this compound be liquefied at room temperature?

Step-by-Step Solution

Answer

Yes, propane can be liquefied at room temperature with sufficient pressure.

Step 1: Understanding Critical Temperature and Pressure

The critical temperature of a substance is the highest temperature at which it can exist as a liquid, regardless of pressure. Above this temperature, the substance can only exist as a gas, not a liquid. The critical pressure is the pressure required to liquefy a gas at its critical temperature.

Step 2: Identify Room Temperature in Celsius

Room temperature is generally considered to be around 25°C. We will use this as the reference temperature to determine if propane can be liquefied at room temperature.

Step 3: Compare Room Temperature with Critical Temperature of Propane

Propane has a critical temperature of 96.7°C. This means propane can exist in a liquid state at temperatures below 96.7°C if enough pressure is applied.

Step 4: Conclusion Based on Temperature Comparison

Since the room temperature of 25°C is below the critical temperature of 96.7°C for propane, it is possible to liquefy propane at room temperature if the pressure applied is equal to or greater than the critical pressure.

Key Concepts

Critical Temperature

The critical temperature is a key concept in the liquefaction of gases. It is the highest temperature at which a substance can exist as a liquid, regardless of how much pressure is applied. Above this temperature, the substance becomes a gas and cannot be liquified.
For example, methane has a critical temperature below room temperature, meaning it cannot be liquefied under normal conditions at room temperature. Critical temperature determines the possibility of a phase change occurring under specific thermal conditions.

Critical Pressure

Critical pressure works hand in hand with critical temperature. It's the minimum pressure necessary to liquefy a gas at its critical temperature. This is a crucial factor in determining if a substance can change from gas to liquid.
In our original problem, propane has a critical pressure of 42 atm at its critical temperature of 96.7°C. To liquefy propane at room temperature, the pressure must be equal to or exceed this critical pressure, as long as the temperature is below the critical point.

Phase Changes

Phase changes involve transitioning between different states of matter—solid, liquid, and gas. These changes occur due to variations in temperature and pressure.
When a gas like propane is subjected to conditions below its critical temperature and at or above its critical pressure, it can condense into a liquid. Understanding phase changes is essential for recognizing how substances behave under different conditions.

Hydrocarbons

Hydrocarbons are organic compounds made entirely of hydrogen and carbon. They come in various forms like methane and propane.
These compounds have specific critical temperatures and pressures, influencing their ability to transition between states. Propane, a simple hydrocarbon, exemplifies how a substance can be liquefied if conditions match its critical requirements. Hydrocarbons' properties are significant in many industrial and scientific applications, including fuel production.