Thermochemistry Lab Report

Chemistry Lab Report Experiment 10 - Determination of Heat Capacity of Calorimeter & Experiment 11 - Calorimetry and the Heat of Neutralization of AcidBase Reactions Discussion Heat capacity of the calorimeter is the amount of heat capacity that can be absorbed for every 1 ¡C change in temperature. Heat capacity can be accomplished by mixing a hot and cold water in the calorimeter. As a result of the mix, the heat lost by the water will be equal the heat gained by the cold water and also by the calorimeter. Therefore, by using the equation ( -qhot water = qcold water + qcalorimeter) it is possible to know the speciÞc heat capacity. Qwater can be replace as Qwater = mcpΔT where (m) stands for mass in grams, (cp) is the heat capacity of the water (4.184 J/g¡C), and (ΔT) is the Þnal temperature of the enthalpy when the liquids are in equilibrium (same temperature). When a acid and base are combined in a neutralization reaction, heat is produced and liberated. The heat produced can be used to determine the molar heat of neutralization (ΔHneut) resulting in the heat released per mole of acid or base reacting. The heat of neutralization qreaction can be determined by using the equation (-qreaction = qsolution + qcalorimeter) where qsolution and qcalorimeter are equal to mcpΔT. The (m) is the mass in grams, so in order to obtain the mass is necessary to convert mL to g by using the density of 1.03 g/mL, (cp) is the speciÞc heat (4.05 J/g¡C), and (ΔT) is is the Þnal temperature of the enthalpy. Example: NaOH+ HC2H3O2 ΔT= (27.6-19.2)¡C = 8.4 ¡C mC=106.25 J/¡C C= 4.05 J/g¡C m= Density x Volume = (1.03 g/ml) (100ml) = 103g -qrxn = qsol + qcal = mcpΔT + mcpΔT = [ (103g) (4.05 J/g¡C) +106.25 J/¡C] (8.4) = 4396.56 J Molarity of HC2H3O2 = 2M or 2mol/ L Volume of HC2H3O2 = 50 ml or 0.04 L M = n/v = 2mol/ L x 0.05L = 0.1 mol ΔHneut = -qrxn/ moles of HC2H3O2 = 4396.56J/ 0.1 mol = 43.9656 kJ/ mol The differences between (q) and (ΔHneu) is that (q) is the amount of heat transferred to the system while the (ΔHneu) is the energy transferred through work. Despite the difference, both are the only methods that energy can be transferred between the system and the surroundings. Qreaction is an intensive property because do not depend on the amount of the substance present, different from (ΔHneu) that depends on the amount of matter being measured. (ΔHneu) = Qreaction/ molacid extensive = intensive It takes more energy to break a weak base bond than to break a weak acid bond. In a acid and base reaction, no bonds are being broken but only being formed; as a result, it must be an exothermic reaction. 1. Constant pursuit of thermal equilibrium between any two sources at different temperatures: the calorimeter and the lid not having a solid efÞcient insulator allows for rapid ßow of energy between the calorimeter and the surroundings, and thus underestimating the ΔH value of the entire process. 2. The splash on the calorimeter: the splash on the calorimeter or the lid from either acid or base from the calorimeter while pouring down into the mixture would create an underestimation in the enthalpy produced from the entire process. The results for the ΔH were considerably reasonable for a Þrst time experiment; moreover, some errors possibly approached during the experiment, which might contributed to some amount of error to the result of the ΔH. Despite this part, the experiment was an excellent opportunity to get more familiar with the lab instruments and a hands on the practice of the laws of thermochemistry. ¥ Summary of ΔHneut values: Acid-Base Reactions ΔHneut values (kJ/mol) HCl / NaOH 43.4422 Strong acid/strong base HCl / NH4OH 43.9656 Strong acid/weak base HC2H3O2 / NaOH 72.2292 Weak acid/strong base HC2H3O2 / NH4OH 64.3782 Weak acid/weak base