Reaction-solution calorimeters results

Calorimetry is the basic experimental method employed in thennochemistry and thennal physics which enables the measurement of the difference in the energy U or enthalpy //of a system as a result of some process being done on the system. The instrument that is used to measure this energy or enthalpy difference (At/ or AH) is called a calorimeter. In the first section the relationships between the thennodynamic fiinctions and calorunetry are established. The second section gives a general classification of calorimeters in tenns of the principle of operation. The third section describes selected calorimeters used to measure thennodynamic properties such as heat capacity, enthalpies of phase change, reaction, solution and adsorption. 

In solute-solvent calorimetry the compound to be studied is present as a mixture with another element or compound in solid form at room temperature and dropped into a hot calorimeter with resulting formation of a liquid product [35], In order to determine the enthalpy of formation of LaBg, Pt was added in a proportion that gave the composition of a low melting eutectic. The liquid phase formed enhanced the reaction rate and enabled the energetic parameters to be extracted [46],... 

When these reactants (both originally at the same temperature) are mixed, the temperature of the mixed solution is observed to increase. Thus the chemical reaction must be releasing energy as heat. This increases the random motions of the solution components, which in turn increases the temperature. The quantity of energy released can be determined from the temperature increase, the mass of the solution, and the specific heat capacity of the solution. For an approximate result we will assume that the calorimeter does not absorb or leak any heat and that the solution can be treated as if it were pure water with a density of 1.0 g/mL. 

Studies using the base-catalysed hydrolysis of methyl paraben (BCHMP) test and reference reaction have been conducted with a variety of different solution-phase flow calorimeters. The results obtained from these studies have shown that the flow rate dependency of the thermal volume is different for each of the instruments used and indeed for each experimental arrangement e.g. sample and reference cell set-up). The determined value for can differ by as much as 15% (over a range of experimental flow rates) from the nominal engineered volume (typically approximately 1ml). This effect can be minimised by careful design of the flow cell and also by careful consideration of the sample and reference cell arrangements (more details can be found in ref. 22 and references therein). 

Inorganic Chemistry of the Main-group Elements as some enthalpies of dilution have been carried out in a reaction calorimeter.170 These results have been combined with some earlier data to obtain the enthalpy of solution of HF as a function of composition, between HF,ooH20 and HF,H20. Vasil ev and Kozlovskii171 have also determined some heats of dilution of aqueous HF calorimetrically as well as heats of neutralization, H++F —> HF, and reaction, H+ + 2F — HF2. There are also some new values of the equilibrium constants for these two reactions.172 Russian workers have also investigated the same equilibria, with aqueous dioxan as solvent.173 Vaillant et al. have redetermined the acidity function for the HF-H20 system for a range of composition.174 Russian workers have reported solubility data for MF3 (M = Eu, Tb, Dy, or Ho)175 and some hexafluorostannates176 in aqueous HF. 

A 50.0-mL sample of 0.400 M copper(II) sulfate solution at 23.35°C is mixed with 50.0 mL of 0.600 M sodium hydroxide solution, also at 23.35°C, in the coffee-cup calorimeter of Example 15-1. After the reaction occurs, the temperature of the resulting mixture is measured to be 25.23°C. The density of the final solution is 1.02 g/mL. Calculate the amount of heat evolved. Assume that the specific heat of the solution is the same as that of pure water, 4.184 J/g-°C. 

A strip of magnesium metal having a mass of 1.22 g dissolves in 100. mL of 6.02 M HCl, which has a specific gravity of 1.10. The hydrochloric acid is initially at 23.0°C, and the resulting solution reaches a final temperature of 45.5°C. The heat capacity of the calorimeter in which the reaction occurs is 562 J/°C. Calculate AH for the reaction under the conditions of the experiment, assuming the specific heat of the final solution is the same as that for water, 4.18 J/g °C. 

Selivanova, Maier, and Luk yanova [63SEL/MAI] prepared CdSe04 H20(cr) and CdSe04(cr) and measured their heats of dissolution in water (1 1200) in a calorimeter. They also measured the enthalpy change of the reaction between the monohydrate and a barium chloride solution with formation of BaSe04(cr). The result of the last reaction has been re-evaluated in Table A-36. 

Sodium hydrogen selenite was prepared and the specimen checked by X-ray and chemical analysis. The enthalpy of reaction between solid NaHSe03 and a solution of lead nitrate with formation of crystalline lead selenite was measured in an electrically calibrated calorimeter. The result is used in Table A-67 to calculate the enthalpy of the reaction NaHSe03(cr) + Pb -> PbSe03(cr) + + Na. ... 

Crystalline K2Se205 was prepared by heating KHSe03 at 343 K. Chemical and X-ray analysis confirmed the composition and crystalline state of the preparation. The salt was reacted with a lead nitrate solution in an electrically calibrated calorimeter. The calorimetric result is used in Table A-81 to calculate the enthalpy change of the reaction KzSejOsCcr) + 2Pb + H20(l) 2PbSe03(cr) + 2K +... 

An excess of zinc metal is added to 50.0 mL of a 0.100 M AgN03 solution in a constant-pressure calorimeter like the one pictured in Figure 6.7. As a result of the reaction... 

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 ... 

NaOH in a coffee-cup calorimeter, the temperature of the resultant solution increases from 21.0 °C to 27.5 °C. Calculate the enthalpy change for the reaction in kJ/molHCl, assuming that the calorimeter... 

The transition from the rapid to the gradually decreasing reaction rate is conventional and depends also on the calorimeter used and the conditions of measurements. It is characterized, however, primarily by transition to the diffusion controlled process, as a result of increasing C-S-H gel content and rising thickness of its layer formed around the anltydrous cores of grains. The supersaturation of solution decreases, which causes and the drop of the rate of crystallization processes. 

When a 6.50-g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee-cup calorimeter (Figure 5.17), the temperature rises from 21.6 to 37.8 °C. (a) Calculate the quantity of heat (in kJ) released in the reaction, (b) Using your result from part (a), calculate AH (in kJ/mol NaOH) for the solution process. Assume that the specific heat of the solution is the same as that of pure water. 

---