Date Performed: November 25, 2010
Coupled Reactions
RESULTS AND DISCUSSION
Overview of Procedures
The determination of heat of reactions involves the use of calorimeters. Since bomb calorimeters (constant-volume) aren’t available for use in the university, one must construct a calorimeter and in this case, a coffee-cup calorimeter (constant-pressure). After the construction of the calorimeter, one must determine its heat capacity by calibration. In calibration, one must conduct a controlled reaction inside the calorimeter with a known Hrxn and measure the temperature change using a thermometer. Using the equations: qcal = CcalT and Hrxn = - qcal / nLR, one can determine the calorimeter’s heat capacity. After the calibration of the calorimeter, one can now proceed to the determination of heat of various reactions.
Significance of Results
Based on the data gathered through experimentation, results showed that the neutralization reactions, the reactions between an active metal and an acid, and the displacement of one metal by another exhibited a positive change in temperature and negative enthalpy values. This means that the reactions released heat and are therefore, exothermic. On the other hand, the precipitation reaction yielded a negative change in temperature which pertains to a reaction that absorbs heat and therefore, endothermic.
The calculated percent errors were abnormally large. The possible sources of errors can be: first, the lid/cork was not replaced immediately after pouring/putting the 2nd reagent in to the test tube. Second, there were some errors on the preparation of the solutions. Third, the temperature readings were taken immediately after a reagent was poured in to the test tube instead of waiting for the temperature to constant/dropping, resulting in smaller measured changes in temperature and thus, affecting the calculated Ccal and in turn jeopardizing the calculations of Hrxn’s
