Hess Law Lab

810 Words4 Pages
Purpose Measure the enthalpy for three reactions and to confirm the value of Hess’ law in predicting the ΔH of a reaction A) NaOH(s) NaOH(aq) B) NaOH(aq) + HCl(aq) NaCl(aq) + H2(l) C) NaOH(s) + HCl(aq) NaCl(aq) + H2O(l) Materials Styrofoam Cup Calorimeter | Forceps | Thermometer | NaOH Pellets | Graduated Cylinder | 0.50M HCL | Beaker | Magnetic Stirrer | Stirring Hot Plate | | | | Procedure Thermometers were used instead of Lob pro. (Refer to lab handout) Observations Table One: Results for Part A: Trial | Mass m / g | Temperature of H2O (±0.1°C) | | Cups | Cups, H2O, Pellets | Cups, Pellets | Initial Ti / °C | Final Tf / °C | Change ΔT / °C | 1 | 7.14g | 56.15g | 8.15g | 19.3°C | 23.0°C | 3.7°C | 2 | 7.49g | 55.17g | 8.48g | 19.4°C | 23.5°C | 4.1°C | 3 | 8.02g | 54.15g | 9.03g | 19.4°C | 23.2°C | 3.8°C | Table Two: Results for Part B: Trial | Mass m / g | Temperature of H2O (±0.05°C) | Temperature of HCl (±0.1°C) | | Cups, H2O, Pellets | Initial Ti / °C | Final Tf / °C | Final Tf / °C | 1 | 104.66g | 21.2°C | 21.1°C | 24.9°C | 2 | 103.40g | 20.2°C | 22.3°C | 24.6°C | 3 | 102.56g | 20.0°C | 22.1°C | 24.7°C | Table Three: Results for Part C: Trial | Mass m / g | Temperature of H2O and HCl (±0.1°C) | | Cups | Cups, H2O, Pellets | Cups, H2O, Pellets | Initial Ti / °C | Final Tf / °C | Change ΔT / °C | 1 | 7.41g | 104.41g | 8.41g | 20.4°C | 23.9°C | 3.5°C | 2 | 7.85g | 103.12g | 8.84g | 20.1°C | 25.0°C | 4.9°C | 3 | 8.33g | 103.01g | 7.61g | 20.2°C | 24.2°C | 4.0°C | Analysis Sample Calculations: Trial One: Part A * ΔH=mH2OcH2OΔtnNaOH * ΔH=48.00g4.18Jg-1K-13.7K0.025mol * ΔH=29694.72Jmol-1=29.69kJmol-1 Sample Calculation: Trial One: Part A: Error * Error=mH2OcH2OΔtnNaOH * Error=0.010.20.01 *
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