What is the pressure, in Pa, in a \({\text{100 c}}{{\text{m}}^{\text{3}}}\)container containing 1.8 g of steam at a temperature of 727 °C? (\(R = 8.31{\text{ J}}\,{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}\))

A.     \(\frac{{{\text{1.8}} \times {\text{8.31}} \times {\text{727}}}}{{{\text{18}} \times {\text{100}}}}\)

B.     \(\frac{{{\text{18}} \times {\text{100}}}}{{{\text{1.8}} \times {\text{8.31}} \times {\text{727}}}}\)

C.     \(\frac{{{\text{1.8}} \times {\text{8.31}} \times {\text{1000}}}}{{{\text{18}} \times {\text{1}}{{\text{0}}^{ - 4}}}}\)

D.     \(\frac{{{\text{1.8}} \times {\text{8.31}}}}{{{\text{1.8}} \times {\text{1}}{{\text{0}}^{ - 4}} \times {\text{1000}}}}\)

C

Several responses in the G2 forms stated that there were too many conversions to do which is a fair comment, but options A and B should have immediately been ruled out as the temperature is given in °C not in Kelvin. It was surprising to see that 38.82% of the candidates opted for answer A.

One respondent stated that the value \({\text{8.314 kPa}}\,{\text{L}}\,{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}\) should have been used for the ideal gas constant, \(R\). The value for \(R\) is given as \({\text{8.31 J}}\,{{\text{K}}^{ - 1}}{\text{mo}}{{\text{l}}^{ - 1}}\) in Table 2 of the Data Booklet, so these were the value and units used.

One respondent stated that the value 0.0821 should have been used instead 8.31 for the ideal gas constant, \(R\), with the data provided. 0.0821 could have been used if the pressure was asked to be calculated in atm and not in Pa.

47.58% of the candidates chose the correct answer C. The question had a reasonably good discrimination index of 0.49.