Collect. Czech. Chem. Commun. 1979, 44, 3425-3433

Evaluation of the temperature responses in colorimetric measurements of chemisorption enthalpies on metal films

Miloš Smutek and Slavoj Černý

J. Heyrovský Institute of Physical Chemistry and Electrochemistry, Czechoslovak Academy of Sciences, 121 38 Prague 2


An analysis was performed of various estimates of the adiabatic temperature Ttot that corresponds to the total heat liberated by a gas dose adsorbed on a metal film in the calorimeter for measurement of chemisorption enthalpies. Besides the two common procedures consisting either in the construction of the adiabatic temperature-time curve or in the extrapolation of the single-exponential cooling part of the actual temperature-time curve to zero time, we have examined estimates of Ttot by extrapolating the cooling exponential to the mid-point between zero time and the temperature maximum (t = tmax/2). Model calculations have shown the merit of the latter extrapolation, particularly in the cases of slow heat evolution. This has been verified on the data measured in the chemisorption of methane and ethane on molybdenum films. Extrapolation to tmax/2 has turned out to be a simple and reasonably reliable procedure for handling the data obtained in film calorimeters.