Enthalpy_Change_of_a_Displacement_Reaction

Alan Williams Enthalpy Change of a Displacement Reaction Data Collection and Processing Quantitative Data: Table 1: Raw Data showing Temperature during 9 minutes (Trail1,2) Time (sec) (±1.0) Temperature (°C)(±0.5) Trial 1 Temperature (°C)(±0.5) Trial 2 0 19.0 20.0 30 19.0 20.0 60 19.0 20.0 90 19.0 20.0 120 19.0 20.0 150 19.0 20.0 180 40.0 30.0 210 45.0 52.0 240 46.0 53.5 270 47.0 54.0 300 48.0 53.5 330 48.0 53.0 360 48.0 52.5 390 47.5 52.0 420 47.0 52.0 450 46.5 51.5 480 46.0 51.0 510 45.5 50.0 540 45.0 49.5 Qualitative Observation: CuSO4 solution Blue aqueous Zn powder Black powder The copper sulfate solution had a blue colour at room temperature, but as the reaction progressed and the zinc powder was added, the warmed up solution became a dark gray colour with red-brown deposits in it. Calculations CuSO4 solution specific heat capacity x Temperature rise x mass of copper sulfate solution = Heat Evolved (kJ) Trial 1 Temperature rise = max temperature rise- initial temperature = 4.2 x (56- 19) x 25.0g = 3.89 kJ Moles of CuSO4 solution Molarity= moles/ volume 1 M= n/0.025 dm3 Moles= 0.025 of CuSO4 solution Enthalpy of this reaction -3.89/0.025 = -155.6 kJ/mol Therefore: Zn(s) + Cu 2+ (aq)Cu (s) + Zn 2+ (aq) ΔH = -155.6 kJ/mol Trial 2 Temperature rise = max temperature rise- initial temperature = 4.2 x (62- 20) x 25.0g = 4.41kJ Moles of CuSO4 solution Moles= 0.025 of CuSO4solution Enthalpy of this reaction -4.41/0.025 = -176.4 kJ/mol Therefore: Zn(s) + Cu 2+ (aq)Cu (s) + Zn 2+ (aq) ΔH=-155.6 kJ/mol ΔH=-176.4 kJ/mol Average enthalpy change (-155.6 kJ/mol+ -176.4 kJ/mol)/2 =-166.0kJ The accepted value in the data book: -218kJ/mol Error Calculation Variables Margin of Error Error Percentage (%) Temperature (°C) ±1.0 Trial 1 (1.0/(56-19)) x 100 = 2.70% Trial 2 (1.0/(62-20)) x 100 = 2.38% Average: 2.54% Time (secs) ±1.0 Min: (1.0/30) x 100 = 3.33% Max: (1.0/540) x 100 = 0.19% Average: 1.76% Volume ±0.05 Sample: (0.05/25) x 100 = 0.2% Systematic Error Total: 2.54% + 1.76% + 0.2% = 4.5% Error Value: 4.5% x 166 = ±7.47 kJ/mol Conclusion and Evaluation The reaction between Zinc and CuSO4 is a displacement reaction where zinc is replaced by the copper. Hence, zinc lose 2 electrons xmaking it Zn 2+ . This exothermic reaction has a negative enthalpy change since heat is released and temperature decreases. The value for the change in enthalpy obtained from this experiment is -166.0 ±7.47 kJ/mol. The data book value for the enthalpy change is -218kJ/mol. This shows the experimental value and the accepted data booklet value are different. The systematic error is 4.5%. The error in this experiment: The difference in value is 52kJ/moles. To find the total percentage error: (52/218) x 100 = 23.85% to 1 significant figure: 20%. Total error- random error = systematic error 23.85 - 4.5 = 19.35% The systematic error is 19.35% The most significant error comes from systematic errors. Error / Limitation Improvement Stirs weren’t consistent. Magnetic stirrer can be used to be more consistent. Heat loss from the exothermic reaction through holes. Insulate the reaction with more layers. The time difference in when the readings were made at the supposed 30 second intervals. Connect a connector and a timer to the reaction to accurately mark the temperature every 30 seconds. Assumption that the density of CuSO4 solution was 1 g/cm3. Weight the mass solution to get the density for more accurate results.