Problem 78 - Chemistry and Chemical Reactivity

Question

A fluorocarbon, \(\mathrm{CF}_{4},\) has a critical temperature of \(-45.7^{\circ} \mathrm{C},\) a critical pressure of \(37 \mathrm{atm},\) and a normal boiling point of \(-128^{\circ} \mathrm{C}\). Are there any conditions under which this compound can be a liquid at room temperature? Explain briefly.

Step-by-Step Solution

Answer

\( \mathrm{CF}_4 \) cannot be a liquid at room temperature because it is above its critical temperature.

Step 1: Understand the Problem

We need to determine if \( \mathrm{CF}_4 \) can exist as a liquid at room temperature, typically around \( 25^{\circ} \mathrm{C} \). This involves checking the ranges of pressure and temperature under which \( \mathrm{CF}_4 \) remains a liquid.

Step 2: Review Critical Temperature and Pressure

The critical temperature is \(-45.7^{\circ} \mathrm{C}\), and the critical pressure is \(37 \mathrm{atm}\). Above this temperature, \(-45.7^{\circ} \mathrm{C}\), \( \mathrm{CF}_4 \) cannot exist as a liquid regardless of the pressure applied.

Step 3: Analyze Room Temperature Conditions

Room temperature is approximately \( 25^{\circ} \mathrm{C} \). Since this is higher than the critical temperature of \(-45.7^{\circ} \mathrm{C}\), \( \mathrm{CF}_4 \) cannot exist as a liquid at room temperature.

Step 4: Conclusion

Given that room temperature \( (25^{\circ} \mathrm{C}) \) is significantly above the critical temperature \(-45.7^{\circ} \mathrm{C}\), \( \mathrm{CF}_4 \) cannot be a liquid at room temperature under any pressure.

Key Concepts

Critical Pressure

Critical pressure is the pressure required to liquefy a substance at its critical temperature. If the temperature is at or below the critical temperature, a substance can potentially exist as a liquid, provided that enough pressure is applied. Above this critical pressure, even when the temperature is below the critical temperature, the substance will always remain in a gaseous state.
For the fluorocarbon \( \mathrm{CF}_{4}, \) the critical pressure is \(37 \text{ atm}\). Once the critical temperature is exceeded, no amount of pressure can make \(\mathrm{CF}_{4}\) transition into a liquid. This is crucial when trying to understand whether a compound can exist in a liquid state under specific conditions.

Fluorocarbon

Fluorocarbons are compounds consisting of carbon and fluorine. These molecules are quite stable and often have high boiling points compared to other organic compounds. This stability is attributed to the strong carbon-fluorine bonds.
\( \mathrm{CF}_{4} \), also known as carbon tetrafluoride, is a simple fluorocarbon. It is commonly used in the electronics industry and has several specific physical properties, such as a boiling point of \(-128^{\circ}\text{ C} \). Due to the low critical temperature of \(-45.7^{\circ}\text{ C}\), this compound is rarely found in liquid form under standard atmospheric conditions.

Phase Diagram

A phase diagram is a graphical representation that shows the physical states of a substance under different temperatures and pressures. It helps to visualize when a substance is in a solid, liquid, or gaseous state.
For \(\mathrm{CF}_4\), examining a phase diagram can verify the conditions under which each phase exists. At pressures above the critical pressure of \(37 \text{ atm}\), the critical temperature of \(-45.7^{\circ} \text{ C}\) is a boundary: above this temperature, no matter the pressure, \(\mathrm{CF}_4\) cannot be liquid. This visualization makes it clearer that at room temperature, \(25^{\circ} \text{ C}\), the compound cannot exist in a liquid state.

Liquid State

The liquid state of a substance is one of the phases of matter characterized by having a definite volume but no fixed shape. Liquids conform to the shape of their container and have free-flowing molecules that can move past one another.
For \(\mathrm{CF}_4\), achieving a liquid state requires specific conditions, mainly staying below its critical temperature and within its critical pressure limits. However, since our room temperature condition of \(25^{\circ} \text{ C}\) is much higher than the critical temperature of \(-45.7^{\circ} \text{ C}\), creating liquid \(\mathrm{CF}_4\) under typical room conditions is impossible. Understanding the constraints of a liquid state in terms of temperature and pressure is key to determining phase transitions in substances.