You may wish to refer to the General Properties of Gases to review concepts and formulae related to ideal gases.

**Problem**

A hydrogen gas thermometer is found to have a volume of 100.0 cm^{3} when placed in an ice-water bath at 0°C. When the same thermometer is immersed in boiling liquid chlorine, the volume of hydrogen at the same pressure is found to be 87.2 cm^{3}. What is the temperature of the boiling point of chlorine?

**Solution**

For hydrogen, PV = nRT, where P is pressure, V is volume, n is number of moles, R is the gas constant, and T is temperature.

Initially:

P_{1} = P, V_{1} = 100 cm^{3}, n_{1} = n, T_{1} = 0 + 273 = 273 K

PV_{1} = nRT_{1}

Finally:

P_{2} = P, V_{2} = 87.2 cm^{3}, n_{2} = n, T_{2} = ?

PV_{2} = nRT_{2}

Note that P, n, and R are the *same*. Therefore, the equations may be rewritten:

P/nR = T_{1}/V_{1} = T_{2}/V_{2}

and T_{2} = V_{2}T_{1}/V_{1}

Plugging in the values we know:

T_{2} = 87.2 cm^{3} x 273 K / 100.0 cm^{3}

T_{2} = 238 K

**Answer**

238 K (which could also be written as -35°C)