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 because it is below its critical temperature.

Step 1: Understanding Critical Temperature

The critical temperature of a substance is the highest temperature at which it can be liquefied by pressure alone. Above this temperature, no amount of pressure can turn the gas into a liquid.

Step 2: Comparing Temperatures

The critical temperature of propane is given as \(96.7^{\circ} \mathrm{C}\). Room temperature is approximately \(20^{\circ} \mathrm{C}\). Compare these two temperatures: \(20^{\circ} \mathrm{C} < 96.7^{\circ} \mathrm{C}\). This means room temperature is below the critical temperature of propane.

Step 3: Conclusion on Liquefaction

Since room temperature (\(20^{\circ} \mathrm{C}\)) is below propane's critical temperature (\(96.7^{\circ} \mathrm{C}\)), propane can be liquefied at room temperature if enough pressure is applied.

Key Concepts

Liquefaction

Liquefaction is the process of a gas turning into a liquid by applying pressure while maintaining a certain temperature. Depending on the substance, the critical temperature plays a crucial role. If the gas is below this critical temperature, it can be compressed into a liquid by increasing pressure. Conversely, if a gas is above its critical temperature, no amount of pressure can cause it to liquefy. For example, methane cannot liquefy at room temperature because its critical temperature is lower than room temperature. In contrast, propane can be liquified at room temperature because its critical temperature (\(96.7^{\circ} \,\mathrm{C}\)) is higher than room temperature. Thus, by leveraging these principles, we can determine how to efficiently handle and utilize gases in various states.

Pressure

Pressure is the force applied per unit area, and it significantly affects the state of gases. In the context of liquefaction, applying pressure can compress molecules of a gas and change it into a liquid, provided the gas is below its critical temperature. - High pressure can cause gases to occupy less volume, leading to liquefaction. - Above the critical temperature, however, pressure alone can't liquify a gas. For instance, propane has a critical pressure of 42 atm. This means at this pressure, and below its critical temperature, propane turns from a gaseous to a liquid form. Properly manipulating pressure is essential for processes like refrigeration, where preserving gases as liquids is critical.

Hydrocarbons

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon atoms. They are categorized based on their structure, such as alkanes, alkenes, and alkynes. Methane (\(\mathrm{CH}_{4}\)) and propane (\(\mathrm{C}_{3} \mathrm{H}_{8}\)) are both hydrocarbons classified as alkanes, meaning they contain only single bonds among the carbon atoms.Hydrocarbons are crucial in energy production, as they can be found in fuels like natural gas and petroleum. Understanding their properties, including critical temperature and pressure, guides decisions for storage and transportation. For example, methane needs to be kept at temperatures far below room temperature for liquefaction, reflecting its low critical temperature. In contrast, propane's higher critical temperature allows it to be liquefied more conveniently.

Gaseous State

A gaseous state is one of the fundamental states of matter where molecules have neither a fixed volume nor shape. This state is characterized by high kinetic energy, causing molecules to move freely and spread to fill their container. - Gases can be compressed significantly under pressure, changing into liquids when cooled below their critical temperature. - Variables like temperature, pressure, and volume are interrelated in gases, a relation governed by laws such as Boyle's and Charles'. Understanding the behavior of gases, such as methane and propane in their gaseous states, is essential in chemical industries. When managing gases, we must consider their critical points to determine how they can be utilized or stored efficiently. In industries, controlling these states allows for processes like the storage of natural gas in liquid form for ease of transportation.