Concerns over the harmful effects of chlorofluorocarbons on stratospheric ozone have motivated a search for new refrigerants. One such alternative is 2,2 -dichloro-1,1,1-trifluoroethane (refrigerant 123). Younglove and McLinden published a compendium of thermophysical properties of this substance (B.A. Younglove and M. McLinden, \(J\). Phys. Chem. Ref Data 23,7 (1994)), from which properties such as the Joule-Thomson coetficient \(\mu\) can be computed. (a) Compute \(\mu\) at \(1.00\) bar and \(50^{\circ} \mathrm{C}\) given that \((\partial H / \partial p)_{T},=-3.29\) \(\times 10^{3} \mathrm{~J} \mathrm{MPa}^{-1} \mathrm{~mol}^{-1}\) and \(C_{p \cdot m}=110.0 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\). (b) Compute the temperature change that would accompany adiabatic expansion of \(2.0 \mathrm{~mol}\) of this refrigerant from \(1.5\) bar to \(0.5\) bar at \(50^{\circ} \mathrm{C}\).

Thermophysical properties are crucial characteristics of materials that define their behavior under various thermal conditions. They include properties such as thermal conductivity, specific heat, thermal expansion coefficient, and in the context of this discussion, the Joule-Thomson coefficient. Understanding these properties is essential for the design and operation of thermal systems, such as refrigeration units, where safety and efficiency are paramount.

In the case of refrigerant 123, a potential alternative for harmful chlorofluorocarbons, calculating its thermophysical properties allows us to understand how it will perform under certain temperature and pressure conditions. These computations are not just theoretical exercises; they are applied by engineers to predict how refrigerants will behave in real-world applications, ensuring that alternatives to harmful substances can be utilized effectively and responsibly.

Adiabatic expansion is a process where a gas or liquid expands in volume without exchanging heat with its surrounding environment. This process is isenthalpic, meaning there is no change in the enthalpy (total heat content) of the system. It is a core concept in thermodynamics and plays a crucial role in refrigeration and air conditioning systems.

Understanding adiabatic expansion helps in predicting the cooling effect when a refrigerant expands within the coils of a refrigerator or air conditioning unit. During this process, the temperature of the refrigerant often drops, which is harnessed to cool the air or contents of a refrigerator. The Joule-Thomson effect, which quantifies the change in temperature during an adiabatic expansion when a real gas or liquid passes through a valve or porous plug, is critical in designing efficient cooling systems.

The molar heat capacity of a substance is a measure of the amount of heat energy required to raise the temperature of one mole of the substance by one degree Celsius at constant pressure. It is denoted by the symbol \(C_{p,m}\) for constant pressure conditions. For refrigerant 123, which we study as an alternative to more harmful substances, knowing its molar heat capacity allows us to calculate how much heat it can absorb or release during phase changes or temperature fluctuations.

The molar heat capacity plays a key role in determining the efficiency of the refrigerant during the refrigeration cycle. By understanding \(C_{p,m}\), engineers can predict how well a refrigerant can carry heat from one place to another, which is essential for the cooling performance of a refrigeration system.