The figure below is a plot of vapor pressure versus temperature for dichlorodifluoromethane, $\mathrm{CCl}_{2} \mathrm{F}_{2} .$ The enthalpy of vaporization of the liquid is $165 \mathrm{kJ} / \mathrm{g},$ and the specific heat capacity of the liquid is about $1.0 \mathrm{J} / \mathrm{g} \cdot \mathrm{K}$. (FIGURE CAN'T COPY)
(a) What is the approximate normal boiling point of $\mathrm{CCl}_{2} \mathrm{F}_{2} ?$
(b) $\Lambda$ steel cylinder containing $25 \mathrm{kg}$ of $\mathrm{CCl}_{2} \mathrm{F}_{2}$ in the form of liquid and vapor is set outdoors on a warm day $\left(25^{\circ} \mathrm{C}\right) .$ What is the approximate pressure of the vapor in the cylinder?
(c) The cylinder valve is opened, and $\mathrm{CCl}_{2} \mathrm{F}_{2}$ vapor gushes out of the cylinder in a rapid flow. Soon, however, the flow becomes much slower, and the outside of the cylinder is coated with ice frost. When the valve is closed and the cylinder is reweighed, it is found that $20 \mathrm{kg}$ of $\mathrm{CCl}_{2} \mathrm{F}_{2}$ is still in the cylinder. Why is the flow fast at first? Why does it slow down long before the cylinder is empty? Why does the outside become icy?
(d) Which of the following procedures would be effective in emptying the cylinder rapidly (and safely)? (1) Turn the cylinder upside down, and open the valve. (2) Cool the cylinder to $-78^{\circ} \mathrm{C}$ in dry ice, and open the valve.
(3) Knock off the top of the cylinder, valve and all, with a hammer.