Thermodynamics Enthalpy of Reaction and Hess s Law Judy Chen Partner Mint Date 13 Sept 2011 Purpose The purpose of this lab is verify Hess s law by finding the enthalpies of the reactions NaOH and HCl NH2Cl and NaOH and NH3 and HCl The overall enthalpy should equals to the sum of enthalpy of the three reactions in order to verify Hess s law Understanding Hess s law would be important when scientist tries to determine the overall reaction when only parts of the reaction are given Hypothesis The hypothesis of this experiment is that the enthalpy of the reaction could be determined by using Hess s law and calorimetry because the enthalpy of the entire reaction is the sum of the enthalpies for each step and using calorimetry the transfer of heat could be determined After such procedure is done stoichiometry could be applied to solve for the energy that was absorbed or released during the experiment and the combination of reactions 1 and 2 should be the same as reaction 3 Equipment 2M Ammonia Solution 25mL 2M Ammonium Chloride solution 25mL 2M Sodium Hydroxide solution 25mL 2M Hydrochloric Acid solution 50mL Distilled Water more than 500mL 250mL Beaker 1 50mL Graduated Cylinder 4 Bunsen burner 2 50mL Calorimeter with lid 2 Thermometer 2 Glycerol few drops Stopwatch 1 Fume hood 1 Dropper 4 Wire gauzes 2 Ring stand 2 Procedure Part1 Determining the Heat Capacity of the Calorimeter 1 Set up a calorimeter with a thermometer placed in the lid add few drops of glycerol if lubrication is needed 2 Measure 25mL of distilled water using a graduated cylinder 3 Close the lid of the calorimeter and swirl it 4 Measure and record the temperature of the water 5 Heat approximately 25mL of distilled water to 70 C in a 250mL beaker 6 Add the heated distilled water into the calorimeter 7 Close the lid of the calorimeter with thermometer 8 using a stopwatch measure the temperature every 20 seconds until 180 seconds 9 repeat procedure 1 8 for another trial Part 2 Determine the Heat of Reaction Reaction 1 NaOH aq HCl aq NaCl aq H2O l 1 Measure 25mL of a 2 0M HCl solution using a graduated cylinder 2 Transfer the HCl solution into a calorimeter 3 Measure and record the initial temperature of HCl 4 Rinse the graduated cylinder with distilled water 5 Measure 25mL of a 2 0M NaOH solution using a graduated cylinder 6 Measure and record the initial temperature of NaOH 7 Add the NaOH solution into the calorimeter as soon as possible because NaOH absorbs water from the surroundings 8 Close the lid of the calorimeter with thermometer in it 9 Swirl the calorimeter as soon a the stop watch sets to start 10 Record the temperature every 20 seconds 11 Repeat procedure 1 10 for another trial Reaction 2 needs to be done in a fume hood NH4Cl aq NaOH aq NH3 aq NaCl aq H2O l 1 Rinse the graduated cylinder and the calorimeter form the previous reaction 2 repeat procedure 1 11 from reaction 1 using NH4Cl instead of HCl 3 repeat Procedure 1 and 2 from this reaction for another trial Reaction 3 needs to be done in a fume hood NH3 aq HCl aq NH4Cl aq 1 Rinse the graduated cylinder and the calorimeter form the previous reaction 2 repeat procedure 1 11 from reaction 1 using NH3 instead of HaOH 3 repeat Procedure 1 and 2 from this reaction for another trial Results Part1 Determining the Heat Capacity of the Calorimeter Trial 1 Trial 2 25mL H2O room temperature C 26 26 25mL H2O heated C 70 70 the solutions after 20 47 48 the solutions after 40 48 50 the solutions after 60 49 52 the solutions after 80 49 52 the solutions after 100 49 52 the solutions after 120 49 52 the solutions after 140 49 52 the solutions after 160 49 52 the solutions after 180 49 52 Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Tmix C 49 5 47 75 Tave C 48 48 qcal J 313 8 52 3 Ccal J C 13 3532 2 4046 Specific heat of water J g C 4 184 4 184 Part2 reaction 1 Determining the Heat of Reaction NaOH aq HCl aq NaCl aq H2O l Trial 1 Trial 2 Temperature of 25mL 2 0M HCl C 27 26 Temperature of 25mL 2 0M NaOH C 30 30 the solutions after 20 37 35 the solutions after 40 38 37 the solutions after 60 40 38 the solutions after 80 40 38 the solutions after 100 40 38 the solutions after 120 40 38 the solutions after 140 40 38 the solutions after 160 40 38 the solutions after 180 40 38 Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Tmix C 37 94 36 31 Tave C 28 7 28 qrxn J 966 504 1303 83 H kJ mol 18 2 30 2 Specific heat of solution J g C 4 184 4 184 Solution g 51 5 51 5 Density of Solution g mL 1 03 1 03 Amount of solutions mL 50 50 Part 2 Reaction 2 Determining the Heat of Reaction NH4Cl aq NaOH aq NH3 aq NaCl aq Trial 1 H2O l Temperature of 25mL 2 0M NaOH C 30 Trial 2 Temperature of 25mL 2 0M NH4Cl C 25 25 the solutions after 20 25 29 the solutions after 40 27 30 the solutions after 60 29 30 the solutions after 80 29 30 the solutions after 100 29 30 the solutions after 120 29 30 the solutions after 140 29 30 the solutions after 160 29 30 the solutions after 180 29 30 Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Temperature of seconds C Tmix C 31 29 56 26 5 Tave C 27 5 28 qrxn J 215 476 235 35 H kJ mol 4 6 8 Specific heat of solution J g C 4 184 4 184 Solution g 51 5 51 5 Density of Solution g mL 1 03 1 03 Amount of solutions mL 50 50 Part 2 Reaction 3 Determining the Heat of Reaction NH3 aq HCl aq NH4Cl aq Trial 1 Trial 2 Temperature of 25mL 2 0M HCl C 26 26 Temperature of 25mL 2 0M NH3 C 25 25 the solutions after 20 30 31 the solutions after 40 32 32 the solutions after 60 32 33 the solutions after 80 32 33 the solutions after 100 32 33 the solutions after 120 32 33 the solutions after 140 32 33 the solutions after 160 32 33 the solutions after 180 32 33 …