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Q. 11.5  Two ideal gas thermometers A and B use oxygen and hydrogen respectively. The following observations are made :

                  Temperature                     Pressure                                              Pressure

                                                           thermometer A                                   thermometer B

                Triple-point of water           1.250\times 10^{5}Pa                              0.200\times 10^{5}Pa

                 Normal melting point        1.797\times 10^{5}Pa                               0.287\times 10^{5}Pa

                    of sulphur

(a) What is the absolute temperature of normal melting point of sulphur as read by thermometers A and B?

Answers (1)

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\\PV=nRT\\

\frac{P}{T}=\frac{nR}{V}

As the moles of oxygen and hydrogen inside the thermometers and the volume occupied by the gases remain constant P/T would remain constant.

The triple point of water(T1) = 273.16 K

Pressure in thermometer A at a temperature equal to the triple point of water (P1) = 1.250\times 10^{5}Pa 

Pressure in thermometer A at a temperature equal to Normal melting point of sulphur (P2) = 1.797\times 10^{5}Pa

The normal melting point of sulphur as read by thermometer A T2 would be given as

T_{2}=\frac{P_{2}T_{1}}{P_{1}}

\\T_{2}=\frac{1.797\times 10^{5}\times 273.16}{1.250\times 10^{5}}\\ T_{2}=392.69\ K

Pressure in thermometer B at a temperature equal to the triple point of water (P'1) = 0.200\times 10^{5}Pa

Pressure in thermometer B at a temperature equal to Normal melting point of sulphur (P'2) = 0.287\times 10^{5}Pa

The normal melting point of sulphur as read by thermometer B T'2 would be given as

\\T'_{2}=\frac{P'_{2}T_{1}}{P'_{1}}\\ T'_{2}=\frac{0.287\times 10^{5}\times 273.16}{0.200\times 10^{5}}\\ T'_{2}=391.98\ K

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Sayak

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