Problem 53 - Chemistry and Chemical Reactivity

Question

A fluorocarbon, \(\mathrm{CF}_{4},\) has a critical temperature of \(-45.7^{\circ} \mathrm{C}\) and a critical pressure of 37 atm. Are there any conditions under which this compound can be a liquid at room temperature? Explain briefly.

Step-by-Step Solution

Answer

No, \( \mathrm{CF}_{4} \) cannot be a liquid at room temperature.

Step 1: Understanding Critical Temperature and Pressure

The critical temperature is the highest temperature at which a substance can exist as a liquid, regardless of the pressure applied. For \( \mathrm{CF}_{4} \), the critical temperature is \(-45.7^{\circ} \mathrm{C}\). This means that at temperatures above \(-45.7^{\circ} \mathrm{C}\), \( \mathrm{CF}_{4} \) cannot exist in the liquid state.

Step 2: Comparing with Room Temperature

Room temperature is typically around \( 25^{\circ} \mathrm{C} \). This temperature is much higher than the critical temperature of \(-45.7^{\circ} \mathrm{C}\). Therefore, at room temperature, it is not possible for \( \mathrm{CF}_{4} \) to be a liquid.

Step 3: Considering Critical Pressure

The critical pressure for \( \mathrm{CF}_{4} \) is 37 atm. Above this pressure, at or below the critical temperature, \( \mathrm{CF}_{4} \) could be a liquid. However, at room temperature (\( 25^{\circ} \mathrm{C} \)), being much higher than the critical temperature, no pressure can make it a liquid.

Step 4: Conclusion

Since room temperature is well above the critical temperature of \( \mathrm{CF}_{4} \), \( \mathrm{CF}_{4} \) cannot exist as a liquid at room temperature, regardless of the pressure applied.

Key Concepts

Fluorocarbon

Fluorocarbons are a class of compounds that consist of carbon atoms bonded exclusively to fluorine atoms. This group of chemicals is known for being highly stable due to the strong bond strength between carbon and fluorine.
This stability makes them resistant to heat, chemical interaction, and degradation.

• Fluorocarbons are often used in refrigeration, as propellants in aerosols, and in the production of polymers.
• They are part of a broader chemical family known as halocarbons, which also includes chlorocarbons and bromocarbons.
• One of the key characteristics of fluorocarbons, such as carbon tetrafluoride (\(\mathrm{CF}_4\)), is their low critical temperature and pressure, as observed in this exercise.

Fluorocarbons like \(\mathrm{CF}_4\) have special properties due to their structure. The arrangement of fluorine around carbon creates a molecule with high symmetry, making it challenging to liquefy under typical conditions.
Understanding these compounds and their physical properties is crucial in applications where extreme thermal stability is required.

Phase Transition

Phase transition refers to the change of a substance from one state of matter to another, such as from solid to liquid, or from liquid to gas. Each compound has specific conditions, including temperature and pressure, under which these transitions occur.

• The critical temperature of a substance is the maximum temperature at which a liquid can exist, regardless of how much pressure is applied.
• For \(\mathrm{CF}_4\), the critical temperature of \(-45.7^\circ \mathrm{C}\) means it cannot exist as a liquid above this temperature.
• The critical pressure is the pressure needed to liquefy a gas at the critical temperature.

When a substance surpasses its critical temperature, it transitions into a supercritical fluid. In this state, the distinction between liquid and gas phases disappears.
For fluorocarbons like \(\mathrm{CF}_4\), at room temperature, they are in a gas phase, as their critical temperature is far below room temperature.

Liquid State

The liquid state of a compound is one of the three primary states of matter, characterized by a definite volume but no fixed shape. Liquids conform to the shape of their container and have particles that are more closely packed than in gases, allowing the liquid to be incompressible to a significant degree.

• Entering and maintaining the liquid state depends on both temperature and pressure.
• For \( \mathrm{CF}_4 \), the conditions required to be in a liquid form—temperature below \(-45.7^\circ \mathrm{C}\) and pressures above 37 atm—are not typical of everyday environments like room temperature.
• At room temperature (around \(25^\circ \mathrm{C}\)), \(\mathrm{CF}_4\) remains gaseous because its particles have too much thermal energy to be confined to the liquid state.

To transform \(\mathrm{CF}_4\) into a liquid at temperatures above its critical threshold, extraordinary pressures would be required, which are not feasible in standard atmospheric conditions. Hence, understanding these conditions helps in predicting the physical state of a substance under various environmental scenarios.