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Enthalpy of a Reaction Lab. To experimentally determine the enthalpy for the reaction between zinc and copper(II) sulfate. Zn (s ) +CuSO 4 (aq ) Cu (s ) +ZnSO 4 (aq ) +217 kJ mol -1. Purpose:
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Enthalpy of a Reaction Lab To experimentally determine the enthalpy for the reaction between zinc and copper(II) sulfate
Zn(s)+CuSO4(aq)Cu(s)+ZnSO4(aq)+217 kJ mol-1 Purpose: To experimentally determine the enthalpy of this reaction. The theoretical value for DH is -217 kJ mol-1 Hypothesis: 217 kJ of energy will be released per mole of copper (II) sulfate.
Data collection Temperature (oC) vs time (minutes) graph Find the final temperature Extrapolate the cooling curve Find the Initial temperature
Data Collection: Amounts of reactants and initial and final temperatures. Qualitative observations of the substances and the reaction: Observations: The copper(II) sulfate is a blue solution and zinc is a silver grey powder before the reaction. During the reaction….. A little bit of copper(II) sulfate was spilled… blah… blah
Data processing Energy released: Q = cmDT Q = (4.18 J g-1 oC-1) (20.0 g) (46.0 oC) = - 3849.28 J Moles of limiting reactant: Moles zinc = 3.00g/65.38g mol-1 = 0.0459 moles Moles CuSO4 = 1.0M x 0.0200 dm3 = 0.020 moles Enthalpy of the reaction: DH = Q/mole = 3849.28/0.020 = -192464 J/mol DH = -192 kJ mol-1
Data Processing Percent Error Percent error = (Theoretical – Experimental) x 100 Theoretical value Percent error = (-217 kJ mol-1 -192 kJ mol-1) -217 kJ mol-1 = 11.5%
Data Presentation Theoretical and Experimental Enthalpy Values
Conclusion • In this experiment, copper(II) sulfate and zinc were mixed in a coffee cup calorimeter in order to determine the enthalpy of the reaction. The experimental value -192 kJ mol-1 was lower than the theoretical value -217 kJ mol-1 by 11.5%. Clearly some heat was lost during this experiment or some of the limiting reactant was spilled. Blah… blah… • (Notice: The numbers for the experimental, theoretical and percent error are used in the conclusion!)
Evaluation The experimental value -192 kJ mol-1 was lower than the accepted value by 11.5%. There are a couple of possible errors that may have occurred during this experiment…. blah, blah… made the heat loss greater than expected and this resulted in a lower value for the enthalpy. In addition… blah blah… some blah… and this …. In the future, the experiment could be repeated with three trials in a better insulating cup. In addition… .. Know how each error affected the results… Suggest an improvement for each weakness.
Final notes – The report is individual • DO NOT email or share copies of your lab reports or data tables with other people, even if you were in the same group in the lab! • Submit a typed copy to turnitin.com or a hard copy if you hand wrote the report. • Submit the rough notes taken during the lab and the instructions for the lab report. (I need the rubric on the back.)