Calorimetry 2: Hot and Cold Reactions Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Before Lab Before coming to lab, complete your prelab write-up, including the prelab problems in the manual. You should meet with your lab partner to work out the details of your procedure before coming to lab. Your procedure and sample calculations or analysis flowchart or outline should be detailed and complete. Your TA will check them before you begin your experiments this week. In Lab While in the lab, keep careful records of your experiments and observations in your notebook. For each experiment, plot T vs. time and calculate the molar H before leaving the lab. Your TA will check your notebook for experimental H values for your two reactions. Uncertainty Analysis While in the lab, estimate the uncertainty in your determination of the temperature change for each reaction. For the HCl + NaOH reaction, use the uncertainties in T, volumes, and all other measured quantities as a starting point. From the uncertainty in each measurement, use error propagation to calculate the uncertainty in each calculated result. Using this step-wise propagation of errors, calculate an uncertainty in Ctotal, as you did last week. For the subsequent reactions, use this uncertainty in Ctotal and the uncertainties in measured temperatures, volumes, and masses. Again, propagate these uncertainties in a stepwise manner to calculate the uncertainty in your H values. For each step in the calculations, follow the error propagation rules as outlined in the section at the start of this manual called Computing Uncertainty in Laboratory Data and Results. You should report your H values with an uncertainty calculated using error propagation. Do the literature values fall within the range given by your uncertainty? Calculate the relative uncertainty in your H results, using the results of your error propagation. After Lab Use your results, data and observations to fill in the data sheets in your manual starting on page 175 for evaluation. Thermodynamic Data for Various Reagents Reagent H0f (kJ mol-1) S0(J K-1 mol-1 ) G0 (kJ mol-1) LiCl (s) -408.61 59.33 -384.39 LiBr (s) -351.21 74.27 -342.00 NaCH3CO2 (s) -708.81 123.01 -607.27 NaNO3 (s) -467.85 116.52 -367.07 NH4NO3 (s) -365.56 151.08 -184.02 Li+ (aq) -278.49 13.4 -293.31 Na+ (aq) -240.12 59.0 -261.9 NH4+ (aq) -132.51 113.4 -79.31 Cl- (aq) -167.16 56.5 -131.23 Br- (aq) -121.55 82.4 -103.96 CH3CO2- (aq) -486.01 86.6 -369.31 NO3- (aq) -205.0 146.4 -108.74
Trustees of Dartmouth College, Copyright 1997–2003