Chemistry Notebook 4

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Chemistry Notebook Name: Kieria Brewer Date: 07/22/2023 Experiment #: 4 Title: Thermochemistry Purpose: To investigate acid/base and combustion reactions Procedure: Experiment 1: Acid/Base Reaction Heat capacity of Calorimeter A coffee cup calorimeter, a thermometer including a stopper, and a cardboard lid are needed. The heat capacity of the calorimeter is determined by adding 50 ml of water to the coffee cup calorimeter. The carboard lid along with the thermometer are placed on top.50 ml of water is placed into a water bath set at 40 o C. After sitting for 5 minutes the temperature is taken and recorded as the initial temperature. The warmed water is mixed into the calorimeter. The temperature is taken and recorded every 15 seconds. The heat capacity of the calorimeter is calculated. Acid/Base reaction 50 ml of HCl are poured into a clean coffee cup calorimeter. 50 ml of NaOH are measured and poured into a beaker. The initial temperature of both solutions is taken and recorded. The 50 ml of NaOH mixed into the calorimeter. The temperature of the mixture is taken every 15 seconds. The change in heat of the solution, the calorimeter, and final enthalpy of reaction is calculated and used to determine the % error. Experiment 2: Combustion Reaction A ring stand containing a copper pan is placed 6 inches from the bench. A graduated cylinder is used to measure 500 ml of water before adding the water into the copper pan. The pan is then covered with a cardboard lid that includes a thermometer and stopper. The initial temperature of the water is taken and recorded. A camp heat can is placed on the balance and the initial weight is recorded. The camp heat can is ignited. The temperature of the water is observed and recorded as it increases to 15 degrees Celsius. The flame is smothered with the lid once the water reaches 15 degrees Celsius. The final temperature of the water is taken and recorded. The camp heat is placed back on the balance to record the final mass. The change in temperature of the water, change in mass of the fuel source, and change in heat for the reaction overall are calculated and used to determine the percent efficiency.

Chemistry Notebook Data/Results/Calculations: Experiment 1: Acid/Base reaction Initial temperature water = 22.5 o C Initial temperature of warm water = 38 o C Highest temp of mixed water = 30 o C To calculate heat capacity of coffee cup calorimeter: Temperature change of tap water = 30 - 22.5 = 7.5 o C= 7.5 K Temperature change of warm water = 38 - 30 = 8 o C = 7.5 K Heat gained by tap water = 7.5K x 50g x 4.18 J/Kg = 1567 J Heat lost by warm water = 8K x 50g x 4.18 J/Kg = 1672 J Heat gained by calorimeter = 1672J - 1567J = 104.5 J Heat capacity = 104.5J/7.5K =13.9J/K

Chemistry Notebook NaOH + HCl →NaCl + H 2 O Initial temperature of HCl = 22.8 o C Initial temperature of NaOH = 22.4 o C Highest temperature of the solution when mixed = 28.6 o C To Calculate enthalpy: Change in temperature = 28.6 - 22.8 = 5.8 o C= 5.8K Heat gained by solution = 5.8K x 100g x 4.18J/gK = 2424.4 J Heat gained by calorimeter = 5.8K x 13.9J/K = 80.6 J Total heat gained = 2424.4J + 80.6J = 2505 J 0.050L HCl x (1mol/1L) x (1 mol H 2 O/1 mol HCl) = 0.050mol H 2 O ∆H = 2505J/0.050mol = 50,100J/mol = 50.10kJ/mol % Error = [(Accepted value - experimental value) /accepted value] x 100 accepted value = 56.2kJ/mol [(56.2kJ/mol – 50.10kJ/mol) / 56.2kJ/mol = 10.9 % Experiment 2: combustion reaction C 4 H 10 O 3 + 5O 2 → 4CO 2 + 5H 2 O Initial temperature of the water = 21.4 o C. Initial mass of the fuel source = 203.2382g. Final temperature of the water = 37.2 o C Final mass of the fuel source = 200.2244g Change in mass = 203.2382 - 200.2244 = 3.0138g Change in temperature = 37.2 - 21.4 = 15.8 o C ∆q = mc∆T ∆q = [(500g x 1cal/gC) + (218.87g x 0.092cal/gC)] x 15.8C = 8218.1 cal Percent efficiency = (actual/theoretical) x100 Accepted value = 6020 cal/g Theoretical value = 8218.1cal/3.0138g = 2726.8 cal/g % efficiency = (2726.8/6020) x100 = 45.3%

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Chemistry Notebook Conclusions: In the acid/ base reaction, the percent error was calculated to be over 10%. This means that the change in enthalpy calculated is not completely accurate. There are several reasons that could have caused the results to be inaccurate. One reason could be that some of the heat produced escaped since coffee cup calorimeter isn’t well insulated and the carboard lid was not flush with the coffee cup. The combustion reaction was performed to determine how much heat would be needed to warm 500 ml by 15 o C. The percent efficiency was calculated to be 45.3%. Having an efficiency this low could be due to a lack of insulation much like the acid/ base reaction. If this experiment could be performed with insulation, better results would be achieved since more heat would be absorbed by the pan and water. Notes:  All reactions have some sort of energy change or heat change.  Thermochemistry= heat associated with chemical reactions  Enthalpy: total energy of a system.  Energy: the potential to do work.  Endothermic reaction = absorbs heat  Exothermic = produces heat.

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