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# Additivity of Heats of Reaction: Hesss Law Design and Data Collection

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Introduction

IB Chem 11 Laura Hu Partner: Rhona Yue Worked together with Zheting and Melissa Additivity of Heats of Reaction: Hess's Law Purpose: To confirm Additivity of Heats of Reaction: Hess's Law. Supplies: As in text. Procedure: As in text. Reactions: Reaction #1: NaOH(s) + H2O(l) Na+ + OH- + q1 q1 is the difference in Heat for reaction 1 in Joules NaOH(s) is about 2.0g, and H2O(l) is 100mL Reaction #2: 100mL of 0.50M HCl(l) + about 2.0g NaOH(s) NaCl + H2O + q2 q2 is the difference in Heat for reaction 2 in Joules Reaction #3: 50.0mL 1.0M HCl(l) + 50.0mL 1.0M NaOH(l) NaCl + H2O + q3 q3 is the difference in Heat for reaction 3 in Joules Data Collection Table #3: Results collected by Rhona and Laura Initial Volume Mass of NaOH [m] Initial Final Temperature [t2] Reaction Temperature [t1] measured � 0.005 (g) � 0.2 (�C) � 0.2 (�C) ...read more.

Middle

+ NaOH(l) 50.0(HCl) + 50.0(NaOH) = 100. Results collected by Zheting and Melissa: (refer to Table #4) Reaction Solution Mass (g) 1 NaOH(s) + H2O(l) 1.97 + 100. = 102 2 HCl(l) + NaOH(s) 100. + 1.98 = 102 3 HCl(l) + NaOH(l) 50.0 + 50.0 = 100. 2. Calculating ?t Note: ?t = t2 - t1 Example Calculation: ?t of Reaction 1 = 22�C - 21�C = 1�C Uncertainty: + 0.2 �C 0.2 + 0.2 = 0.4. ?t has an uncertainty of 0.4 �C Results collected by Rhona and Laura: Reaction t1 (�C) t2 (�C) ?t (�C) 1 21 22 1 2 20.9 26.5 5.6 3 20.4 26.7 6.3 Results collected by Zheting and Melissa: Reaction t1 (�C) t2 (�C) ?t (�C) 1 25 29 4 2 21 32 11 3 21 28 7 3. Calculating q Note: q = Cp � m � ?t (Heat Capacity [Cp] = 4.18J/g�C) Example calculation: q of Reaction 1 = 4.18 J/g x 103g x 1�C = 430.54 J 1000 J = 1 kJ , ...read more.

Conclusion

?H / mols of NaOH Note: ?H is taken from part 4 and mols of NaOH is taken from part 5. Sample calculation: Reaction 1: -0.431 kJ / 0.0574 mol = Results collected by Rhona and Laura: Reaction ?H/mol NaOH (kJ/mol) 1 -5.88 2 -33.6 3 -52.6 Results collected by Zheting and Melissa: Reaction ?H/mol NaOH (kJ/mol) 1 -34.7 2 -94.7 3 -58.6 7. Theoretically, heat of reaction 1 + heat of reaction 3 = heat of reaction 2. Results collected by Rhona and Laura: Heat of Reaction 2: -33.6kJ/mol Combined heat of reaction 1 and 3: -58.48kJ/mol excesses the number for heat of reaction2. Percentage error: Experimental value � 100 Accepted value -58.48 kJ/mol � 100 = 174% Unrealistic - 33.6 kJ/mol Results collected by Zheting and Melissa: Heat of Reaction 2: -94.7kJ/mol Combined heat of reaction 1 and 3: -93.3kJ/mol Percentage error: Experimental value � 100 Accepted value - 93.3 kJ/mol � 100 = 98.5% - 94.7 kJ/mol ...read more.

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