Calorimetry Prelab

Experiment 12 Calorimetry and Heat of Reactions ____________________________________________________________________________________________________________ PERFORMANCE GOALS 1. To learn how to use of a calorimeter 2. To learn how to collect and manipulate data in the computer 3. To maneuver the calorimeter constant 4. To use Hess righteousness to find the combust or formation of atomic number 12 oxide CHEMICAL OVERVIEW Enthalphy (? H) when chemical or physical changes occur at a constant pressure. Calorimeter is an instrument with insulating walls where the reaction happens. Eq. 1 q rxn = -qsurrounding Heat of capacity of the calorimeter Cp must be calculated at the beginning of every calorimeter experiment in Joules/ C Heat Capacity of the Calorimeter The calorimeter constant is easily found by adding a bushel amount of hot water to a known amount of cold water and the change in temp for each recorded, due to the Law of goose egg Conservation the amount of heat released by t he hot water should be equal to the amount of heat intent by the cold water Eq. 2 q released( Hot water) = -q absorbed ( stone-cold Water) If there is a discrepancy between these two values use the following equationEq. 3q= m x spht x ? T Where spht is the specific heat of the substance in J/ gC ?T is the temperature change in C andm is the mass in grams potty of Cold Water51. 20 g initial temperature of cold water20. 3 C gage of hot water49. 82 g Initial temp of hot water98. 2 C Final temp of the mixture58. 3 C Eq. 4qHot = mHot x sphtWater x ? THot qHot = (4. 184 J/ C-g)(49. 82g)(58. 3 C-98. 2 C) = -8317 J Eq. 5qCold = mCold x sphtWater x ? TCold qCold = (4. 184 J/ C-g)(51. 20g)(58. 3 C-20. 3 C) = 8142 J 8317-8142 = 175 joules Cp = ( 175 J ) / (58. C 20. 3 C) Cp = 4. 6 J/ C take fire OF REACTIONS q released = -q absorbed Eq. 6 q released = (q solution + q calorimeter ) Eq. 7 qSolution = mSolution x sphtWater x ? TSolution sphtsolution= 4. 184 J/ g C Eq. 8q calorimeter= Cp x ? T Eq. 9 q reaction = ? Hreaction Hesss Law Hesss Law adduces that the enthalpy of a reaction is independent of the steps that it takes to get from reactants to products because enthalpy of reaction is a state function. State Function- depends on initial and concluding state but not on the path taken ?Temperature ?Volume ?Pressure ?Energy Mg (s) + 1/2 O2 (g) MgO ( s) PRE-LAB ASSIGNMENT 1. Predict the product, balance the questions and redeem the net ionic equations for the reactions a. Mg (s) + HCI (aq) b. MgO (s) + HC (aq) 2. Write the reaction that represents the enthalpy of formation ( ? Hfor ) of water. 3. Use the table of the thermodynamic data in your text book to calculate the ? H for each of the three reactions REMEMBER Eq. 10 ( ? H rxn = ? ( n? H for )prod ? ( n? H for )react 1) 2) 3) 4. Use Hesss Law combining the three molecular equations to calculate the ?Hrxn for the reaction of the formation of MgO. PROCEDURE A. CALIBRATION OF THERMISTOR 1. 2. 3. 4. 5. 6. 7. B . DETERMINATION OF THE HEAT CAPACITY OF THE CALORIMETER 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. C. REACTION OF MgO AND HCI 1. 2. 3. 4. 5. 6. 7. 8. 9. D. REACTION OF Mg AND HCI 1. 2. 3. 4. 5. 6. 7. E. DATA AND CALCULATIONS A. Calorimeter Constant quid of Styrofoam cup with lid + spin bar (g) Mass of cup with lid + spin bar + 50mL of room temp. water (g) Initial Temp of Room Temp. Water ( C ) Initial Temp of Hot Water( C ) Total mass at the end (g) cipher Heat released by Hot Water (J) (Eq. 4) Calculated Heat absorbed by R. T Water (J) Eq. 5) Calculated Heat absorbed by Calorimeter (J) Calculated Heat Capacity of the Calorimeter, Cp (J/C) (Eq. 8) B. Heat of Reaction of MgO Mass of weighing boat (g) Mass of weighing boat + Magnesium oxide (g) Mass of Magnesium oxide (g) Mass of Styrofoam cup with lid + spin bar (g) Mass or Styrofoam cup with lid, spin bar (g) + HCI Calculated Mass of HCI (g) Total Mass of solution at the end Calculated Mass of MgO (g) (using total mass of solution)Initial Tem perature of Solution (C) (before MgO was added) Final. Temp of solution (C) (after MgO was added) Calculated Heat absorbed by solution (J) (Eq. 7) Calculated Heat absorbed by calorimeter (J) (Eq. 8) Calculated Total heat absorbed Calculated Total heat released by the solution (Eq. 6) Calculated counterspys of MgO Calculated Moles of HCI Heat released per Mole of MgO Molar Heat Reaction (kJ/mol) C. Reaction of Mg with HCI Mass of weighing boat (g) Mass of weighing boat + Magnesium (g) Mass of Magnesium (g) Mass of Styrofoam cup with lid + spin bar (g)Mass or Styrofoam cup with lid, spin bar (g) + HCI Calculated Mass of HCI (g) Total Mass of solution at the end Calculated Mass of Mg (g) (using the final mass of solution) Initial Temperature of Solution (C) (before Mg was added) Final. Temp of solution (C) (after Mg was added) Calculated Heat absorbed by solution (J) (Eq. 7) Calculated Heat absorbed by calorimeter (J) (Eq. 8) Calculated Total heat absorbed Calculated Total heat releas ed by the solution (Eq. 6) Calculated Moles of Mg Calculated Moles of HCI Heat released per Mole of Mg