Question

A constant-volume gas thermometer registers an absolute pressure corresponding to 325 mm of mercury when in contact with water at the triple point. What pressure does it read when in contact with water at the normal boiling point?

Short answer

The pressure reading when there is contact with water at normal boiling point is 444mm of mercury.

Step-by-step solution

Step 1: Identification of given data

Absolute pressure corresponding to 325 mm of mercury

Concept of Triple point.

Triple point is a singular point designating pressure and temperature at which the three phases. i.e. solid, liquid and gas of any pure substance can exist at the same time while in equilibrium.

Determination of the pressure at the temperature where CO2 solidifies.

The volume in this case is constant. Therefore, the relation connecting the temperature and pressure is,

Solve for P,

$$\begin{gathered} P=P_{triple}\left[\frac{T}{T_{triple}}\right] \\ \mathrm{For}\mathrm{mercur}y,P_{triple}=325mm,T_{triple}=273.16k \\ T={100}^{°}C+273.16\mathrm{K} \\ =373.16\mathrm{K} \end{gathered}$$

Substitute all the values in the above equation,

$$\begin{gathered} \mathrm{P}=(325.0\mathrm{mm})\left[\frac{375.16\mathrm{K}}{273.16\mathrm{K}}\right] \\ =444\mathrm{mmof}\mathrm{mercury} \end{gathered}$$

Thus, the pressure reading when there is contact with water at normal boiling point is 444 mm of mercury.