Post Lab 3- Experiment 3

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May 5, 2024

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Date: 07/10/2023 Amaya Strauss CHEM 1215L-011 Experiment 3: Determination of Enthalpy for a Reaction Using Calorimetry Partner Names: Jackie Crump, Jana Valdez Deangelo & Martha Patterson
Data Analysis Example Calculation of Enthalpy: Equation: ΔHrxn = Σ ΔHproducts – Σ ΔHreactants Example: HSO4^-(aq) SO4^2- (aq) + H(aq) ΔH of HSO4^- = -885.75 kJ/mol (as per lab manual) ΔH of SO4^2- = -907.51 kJ/mol (as per lab manual) ΔH of H= 0 ΔHrxn = Σ ΔHproducts – Σ ΔHreactants ΔHrxn = -907.51 + 0 – (–885.75) ΔHrxn = –21.76 kJ/mol (–) indicates exothermic reaction Example Of Finding Standard deviation: Equation for Standard Deviation : x = recorded data points = mean of data points x̄ n = number of data points Example: Find the standard deviation for data points with average densities of 1.36, 1.6, and 1.54 g/ml. x= 1.36, 1.54, 1.60 =1.5 x̄ n=3 = 0.12489996 or 0.125 g/ml Equation for Percent Error: Percent error = (experimental – true/true) x 100 Error Analysis: Below are the calculated means and standard deviations for trials 1-4 for HCL and NaHSO4. In order to find these values, the change in temperature of each trial were used. Change in temperature can be calculated using the equation: ΔH= Temperature (final) -Temperature (initial)
Below are the calculated enthalpies( ΔH) in kJ/mol for each reaction of HCl/NaOH and NaHSO4/NaOH using mean values calculated above. These values were calculated using several values/eqns, such as: Cs of water= 4.18 J/g*k as per lab manual Mean temperature changes for HCl and NaHSO4 Total volume of rxn (20ml base & 21 acid)=41mL or 41g Qrxn= - Qcal Additionally, in order to determine the percent errors for these reactions, the following calculations were made in order to find the true value of the experiment. The values of ΔH for each product/reactant can be found in the lab manual on page 105 (109 pdf). The calculations can be seen below:
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Calculated enthalpies( ΔH)
These values show that the ΔH of reaction HCl was an exothermic reaction, where ΔH = -55.9kJ/mol, and that NaHSO4 was also an exothermic reaction, where ΔH= -70.5kJ/mol. The percent error for HCl was 0.01% and was 9.17% for NaHSO4. ΔHrxn of HSO4 = -70.5-(-55.9kJ/mol)= -14.6 kJ/mol Summary of Experimental Results Below are the results from data collection in lab, showing the concentrations and amounts in mL of each acid and base used for each four trials of the two different combinations. The initial and final temperatures were used to calculated the change in temperature, or ΔH, in degrees Celsius of each reaction.
Conclusion: As seen above previously in Error Analysis , the percent error for both HCl and NaHSO4 reactions were both under 15%. Therefore, this shows good accuracy for this experiment. Additionally, the Standard Deviations for this experiment were under 1, showing that the data in this experiment was precise. All of this therefore shows that the experiment was performed well and the data is reliable. Therefore, my hypothesis was proven, and the experiment overall was a success. Discussion A) Using Appendix B to calculate the enthalpy of dissociation of hydrogen sulfate from the enthalpies of formation. HSO4^-(aq) SO4^2- (aq) + H(aq) ΔH of HSO4^- = -885.75 kJ/mol (as per lab manual) ΔH of SO4^2- = -907.51 kJ/mol (as per lab manual) ΔH of H= 0 ΔHrxn = Σ ΔHproducts – Σ ΔHreactants ΔHrxn = -907.51 + 0 – (–885.75) B) ΔHrxn = –21.76 kJ/mol (–) indicates exothermic reaction C) Comment on the enthalpy you obtained from the experiment to the calculated one. Do they match? Evaluate on the success of this experiment. HSO4^-(aq) SO4^2- (aq) + H(aq) For my experiment, the enthalpy of hydrogen sulfate was calculated as ΔH= - 14.6 kJ/mol. The true value for this was supposed to be -21.76kJ/mol. Therefore, the percent error overall for this experiment is -14.6-(-21.76)/-21.76 X100= - 32.9%
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Overall, although each reaction was very low percent error wise, and the calculated value for hydrogen sulfate was relatively close to true one, this experiment was only somewhat a success, because the overall error was over 15%. In Class Calculations/Data Collection

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