Accuracy reaction-solution calorimeters

Various substances and reactions have been used to test the accuracy of reaction-solution calorimeters [3 9,40]. The solution of tris(hydroxymethyl)amin-omethane (THAM orTRIS) in 0.1 mol dm-3 HCl(aq), which was first proposed by Wadso and Irving [133] in 1964 and recommended by the Standards Committee of the U.S. Calorimetry Conference in 1966 [134,135], is perhaps the most widely used method. Several problems encountered in the use of the THAM+HC1 (aq) reaction to assess the accuracy of reaction-solution calorimeters have been... 

The accuracy of a titration calorimeter is normally assessed using the reactions of NaOH(aq) with HCl(aq) or HCICUjaq) [209,210], The dissolution of crystalline tris(hydroxymethyl)aminomethane (THAM) in HCl(aq) has also been employed when the apparatus is equipped with a system for the introduction of solid samples (e.g., an ampule breaking device) [210]. As mentioned in chapter 8, the latter method is commonly recommended for testing conventional reaction-solution calorimeters [39,40]. 

Manin and Korolev reported having measured the enthalpy of solution of NiC Ccr) into water and into aqueous solutions of other electrolytes. The measurements were performed with an isoperibol calorimeter with a claimed accuracy of 0.6%. Their results for the enthalpy of solution into H2O are listed in Table A-25. The mean value of Aj i//° for the reaction ... 

The amount of ammonia consumed was obtained from the change in mass of a reservoir and the amount of hydrogen fluoride formed was determined after it had been absorbed by solid sodium fluoride. The accuracy of the result was limited principally by the uncertainty in the correction applied for the non-ideality of hydrogen fluoride. An improved calorimeter has been described in which the hydrogen fluoride formed is absorbed in water contained in a PTFE-lined vessel below the combustion chamber, so that the final product is an aqueous solution of hydrofluoric acid. This calorimeter has been used to study the reactions ... 

Auxiliary measurements of enthalpies of dilution are necessary to obtain the enthalpy of reaction between two substances from measurements of the change in enthalpy when solutions of those substances are mixed. This additional labour may often be avoided and greater accuracy obtained by the use of a differential calorimeter in which the dilution process takes place... 

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